REPUBLICA BOLIVARIANA DE VENEZUELAMINISTERIO DEL PODER POPULAR PARA LA DEFENSA

UNIVERSIDAD EXPERIMENTAL DE LAS FUERZAS ARMADASUNEFA PUERTO CABELLO EDO CARABOBO

ENGLISH HOMEWORK

Ship Stability and Construction for Applicants to the Fourth-Class Engineer Certificate

13.1 Introduction

This annex was developed in response to Table A-III/1 of the STCW Code, Maintain seaworthiness of the ship. It will enable the applicants who can not get the basic training on this subject to reach the level of competence required in order to obtain an STCW-endorsed certificate.

Applicants who intend to complete this annex in lieu of the approved training need to have on hand good manuals on ship stability and naval architecture.

One should expect that with proper documentation in hand, approximately 40 hours will be required to complete this annex; upon completion, it must presented to a Marine Safety examiner for assessment.

13.2 Objective

The objective of this annex is three fold, namely:

1. to ensure basic working knowledge and application of stability, trim and stress tables; 2. understanding of the fundamentals of watertight integrity and actions to be taken in the event of partial

loss of intact buoyancy; and 3. general knowledge of the principal structure members of a ship and the proper names for the various

parts.

13.3 Ship Stability

(1) Basic knowledge and definitions

What is the Centre of Gravity of a ship?

What is the Centre of Buoyancy?

What is the transversal Metacentre?

What is the longitudinal Metacentre?

What do the acronyms TPC and TPI stand for? What do they mean?

What do the acronyms MCTC and MCTI stand for? What do they mean?For a specific ship, where can we find the information on the above?

Define briefly the following terms:

Displacement

_________________________________

Deadweight

_________________________________

Coefficient of form _________________________________

Waterplane area

What is Free Surface Effect? Generally speaking, how does this affect the stability of a ship?

What is meant by the trim of a ship? What makes it change?

With regard to a ship's hull, what do Hogging and Sagging mean? How are they measured?

How do we find the stress in a ship's hull? How can one find the maximum allowable stress?

Define the propeller pitch. What is meant by Propeller slip?

State and explain Archimedes's law.How is the draft of a ship affected by the density of the water in which it floats? What is meant by Fresh Water Allowance?

Explain what happens to the ship's centre of gravity when cargo is added or removed. In which direction does it move?

What is the effect of a weight suspended from a crane boom?

What is the Righting Arm? How is it calculated?

What is meant by Intact Stability?

________________________________________What is the purpose of watertight bulkheads?

Where are they installed on a ship?

Describe the fitting of a watertight bulkhead valve. What arrangement is provided to control this valve from outside the compartment?

What is the function of the watertight doors on board a ship? Where are they located? When are they used?

Describe an arrangement provided to close a watertight door from outside the compartments it isolates. Why does it have an alarm? Where and when does it sound?

Explain how you would make a temporary repair to stop the water entering the engine room through a corroded spool between a sea water inlet valve and the ship's bottom.

(2) Exercises

What is the weight of a steel block 1m x 1m x 0.5m having a density of 7500 kg/m3 ?

According to Archimedes's law, what is the weight of this same block when it is immersed in water having a density of 1000 kg/m3 ?Calculate the TPC of a box shaped barge 20m long by 5m large floating in water of 1000 t/m3.

What will be the change in the mean draft of this barge when 500t of cargo are discharged?____________________________________________________________________________________________

Draw a diagram of the midship cross section of a general cargo vessel and show the relative positions of the Centre of gravity (G), Centre of buoyancy (B) and Metacentre (M). Give the typical values in meters relative to the keel (K).

 

 

Draw the same diagram at an angle of 10° and show the righting arm. Give the value relative to the ship's displacement.

 

 

13.4 Ship Construction

(1) Basic knowledge and definitions

Define the following terms relating to a ship's structure:

Frame

_________________________________

Longitudinal framing _________________________________

Transverse framing _________________________________

Web frame _________________________________

Stringer

_________________________________

Floor _________________________________

Deck Girder

_________________________________

Beam knee

_________________________________

Pillar

_________________________________

Bracket

_________________________________

Bilge plate _________________________________

Double bottom

_________________________________

(2) Exercises

Explain the purpose of double bottoms

Draw and label a transverse framed double bottom

 

 

Define Pounding and Panting. How are these stresses compensated for?

Draw and label the midship cross section of the vessel you are presently working on, or one that you are familiar with.

 

 

Sketch and describe the construction of the bow section of the vessel you are presently working on, or one that you are familiar with. Name all the members.

 

 

Sketch the steering gear arrangement of the vessel you are presently working on, or one that you are familiar with, and explain its operation. Explain also the operation of the emergency gear.

 

 

Sketch and describe the rudder of the vessel you are presently working on, or one that you are familiar with. Show in detail one pintle bearing.

 

 

Draw the shafting arrangement of the vessel you are presently working on, or one that you are familiar with, showing also the thrust bearing and how it is attached to the structure.

 

 

Sketch and describe an oil-lubricated stern tube, showing how it is fitted in the ship's structure.

REPUBLICA BOLIVARIANA DE VENEZUELAMINISTERIO DEL PODER POPULAR PARA LA DEFENSA

UNIVERSIDAD EXPERIMENTAL DE LAS FUERZAS ARMADASUNEFA PUERTO CABELLO EDO CARABOBO

HANDOUT Nº 2 10%

MARINE ENGINEERINGMarine Engineering involves the design, construction, installation, operation and support of the systems and equipment which propel and control marine vehicles, and of the systems which make a vehicle or structure habitable for crew, passengers and cargo.[1]

Marine Engineering is allied to mechanical engineering, although the modern marine engineer requires knowledge (and hands-on experience) with electrical, electronic, pneumatic, hydraulic, chemistry, control engineering, naval architecture or ship design, process engineering,steam generation, gas turbines and even nuclear technology on certain military vessels.

Marine Engineering on board a ship refers to the operation and maintenance of the propulsion and other systems such as:electrical power generation plant; lighting; air conditioning; refrigeration; and water systems on board the vessel. This work is carried out by Marine Engineering Officers, who usually train via cadet ships sponsored by a variety of Maritime organisations. There are also training centres at post-secondary institutions that offer marine engineering programs, such as Georgian College's Great Lakes International Marine Training Centre.

Marine engineering also embraces other areas such as Autonomous Underwater Vehicle research; Marine renewable energy research; and careers related to the Offshore Oil and Gas extraction and Cable Laying industries.

History of Marine Engineering

One of the most notable historical figures in Marine Engineering was Archimedes, who experimented with buoyancy; developed the water screw; and pre-industrial naval weapon systems. Pioneers in Marine engineering in Britain include William Froude, and Isambard Kingdom Brunel, who was responsible for demonstrating the effectiveness of the screw propeller, amongst other notable achievements. The oldest surviving marine engine was designed by William Symington in 1788; original engines from the revolutionary 'Turbinia', which proved the superiority of steam-turbine power still survive. In America, the University of Michigan's Department of Naval Architecture and Marine Engineering can be tracked to an 1879 act of Congress, which authorised the U.S. Navy to assign a few officers to engineering training establishments around the country. Mortimer E.

Cooley was the first lecturer in the department.[citation needed] India's Marine Engineering & Research Institute can trace its origins to 1929.[citation needed]

Marine Engines

Marine engineering emerged as a discipline with the arrival of Marine Engines for propulsion, largely during the latter half of the 19th century. Early marine engineers were known as "stokers" as they 'stoked' the coal fires of steam engined ships more or less from the middle of the 19th to the middle of the 20th centuries; the term is still used affectionately by modern ship's engineering staff to describe their role.

Modern mechanical propulsion systems generally consist of a motor or engine turning a propeller. Steam Engines were first used for this purpose, then Steam Turbines, but have mostly been replaced by two-stroke or four-stroke Diesel Engines, Outboard Motors, and with Gas Turbine engines on faster ships. Electric Motors have sometimes been used, especially on submarines. Nuclear reactors are sometimes employed to propel warships and icebreakers.[citation needed]

There are many variations of propeller systems, including twin, contra-rotating, controllable-pitch, and nozzle-style propellers. Smaller vessels tend to have a single propeller. Aircraft carriers use up to four propellers, supplemented with bow-thrusters and stern-thrusters. Power is transmitted from the engine to the propeller by way of a propeller shaft, which may or may not be connected to a gearbox.[citation needed]

Propeller shafts

Several type of propeller shafts exist with their own type of lubrication[2]>. These types are:

Water lubricated propeller shaft [3]

Oil-lubricated propeller shafts Grease lubricated propeller shafts

Water-lubricated propeller shafts are the types which are most maintenance-free and durable. A small disadvantage is that when the bearings become old, they become less efficient. Oil-lubricated propeller shafts as well as grease-lubricated propeller shafts leak some oil, thus being less environmentally-friendly. In some countries, the grease-lubricated variant is therefore already banned. Oil and grease lubricated variants also require more maintenance, and the grease variant also needs to be manually or electronically corrected every few hours of boating (the "grease pot" then needs to be screwed up one notch). The benefits of the oil and grease variants is that they are more efficient.[4]

What Is Naval Engineering?

Naval engineering is a rewarding career that offers challenge, excitement and satisfaction. It is an opportunity to enjoy your proficiency in mathematics and science in a career both steeped in tradition and at the cutting edge of technology. You can be a recognized professional serving one of America's most honored and historic industries, in a technical field where you can see and take pride in the product of your effort.

As a naval engineer, you can design, build, operate or maintain ships as diverse as Navy aircraft carriers and submarines, Coast Guard cutters, or commercial passenger and cargo vessels.

A choice to become a naval engineer will lead you to a broad variety of engineering and physical science skills.

CAREER OPPORTUNITIES

Naval architects must have a general understanding of all engineering disciplines because they generally start the process of designing a ship. After they determine its basic size and shape, they address hull form and resistance, propulsion power requirements, ship structure, weight distribution, stability and the efficient location of the many compartments throughout the ship. 

Marine engineers are responsible for designing mechanical systems for propulsion and auxiliary services, and selecting the associated equipment such as steam boilers and turbines, diesel and gas turbine internal combustion engines, gears.

Mechanical engineers design specific items of machinery like cranes, hoists, elevators, and equipment for anchoring, steering, controlling submarine depth, or moving weapons and other supplies within the ship as well as between ships at sea. A knowledge of fluid systems is required for designing fuel, lubrication and water installations, as well as firefighting, compressed air, and heating, ventilating, and air conditioning.

Civil engineers specify the actual structure of the ship including framing, shell, decks, bulkheads and equipment foundations. They ensure that the ship can withstand the weight of cargo loading and the impact of waves. Combat ships must be able to withstand battle damage from weapons such as missiles, torpedoes and underwater mines.

Electrical engineers provide for the generation and distribution of electricity throughout the ship for lighting, power, system controls and various other ship's services. Today's ships also require a multitude of electronic navigation, communication, and combat systems. 

Ocean engineers concern themselves with work both on and below the surface of the sea and study ocean movements and their effect on ships and craft both on the surface and submerged. An ocean engineer may design small sub-surface vehicles and devices intended for deep submergence that perform ocean bottom scanning, salvage operations, object recovery and submarine rescue. The work includes structural, propulsion, and hull form design for resisting deep ocean pressure, and selection of materials for this hostile environment.

CAREER PATHS

Combat systems and technologies related to Command, Control, Communications, Computers, Intelligence, Surveillance, and Reconnaissance (C4ISR) constitute the most exciting, challenging, and rapidly changing fields in naval engineering. Weapons systems include guns, missiles, torpedoes, and the weapons carried by Navy aircraft. Their design includes place-ment in the ship and integration of equipment such as radar, sonar, periscopes, launchers, and missile control systems (including lasers and satellites). Weapons design, installation, and operation require a variety of disciplines including aeronautical engineering for air frames, chemical engineering for propulsion, electronics engineering for tracking, guiding and controlling, physics for acoustics and electro-optics, and mechanical engineering for loading, rotating and elevating weapons launchers.

Shipbuilding is the process of converting a design into steel. For the shipyard engineer, it involves planning, scheduling and industrial engi-neering for shop and welding procedures, and modern con-struction techniques. Each action in building the ship must be defined in detailed drawings and standard procedures. Every shipyard laborer must have direction as to what he must accomplish each day if the ship is to be delivered on time and at cost. Shipyards also do repair, conversion, and modernization, all of which require these same skills.

Research, development, test and evaluation offer the naval engineer a unique and creative opportunity to perform collaborative work with scientists. The process of developing an engineering concept begins with fundamental theories and ideas, and proceeds through scientific analyses, feasibility studies, collection and analysis of data, design, simulation and modeling, fabrication, model testing, evaluation at sea, and final adoption. RTD&E depends on the physical sciences such as physics, chemistry and metallurgy. This field of naval engineering spans the entire spectrum of engineering and scientific disciplines, and applies to issues such as advanced hull forms, behavior of ships at sea, and development of new materials and technical processes.

PARTS OF A SHIP

Starting from bow to stern:

ForestayA line of rope that holds the mast up

GenoaA large triangular sail that helps the boat turn and power the boat

JibsheetA rope attached to the jib or genoa to place in a position relative to the wind

MastA large pole that holds the genoa/jib and mainsail up

KickerChanges where the point of most power is in on the mainsail up and down (used to decrease or increase sail power depending on wind strength - decrease sail power in high winds and vice versa)

Jib CleatsStoppers in which you place the jib sheet in so that it stays on its current setting

Toe strapsUsed to place your feet in so that you can hike out the boat, without any danger of falling out

CentreboardA large board that can be pulled up or down depending on the point of sail

BenchA small sitting area for the crew

MainsailA large sail that powers the dinghy through the water

CunninghamTakes away the luff in the mainsail created when the slot is too small (only when beating and when there is a lot of wind)

MainsheetA length of rope that allows the mainsail to be pulled in or out with relative ease

OuthaulChanges where the point of most power is in on the mainsail forward and backwards (when viewed looking at the bow)

Mainsheet cleatA stopper to allow the mainsail to remain in its current configuration

Self bailersWhen water comes into the cabin, they pump out water when the boat is reaching

Tiller ExtensionA long pole that allows the tiller to be moved whilst hiked out or when sitting further up the cabin (nearer the mast)

TillerA short pole that is connected to the rudder

RudderA board in a shape similar to the centreboard that allows the change of direction in a boat

BungsStop water entering the bilge and causing the boat to sink

STRUCTURAL KEEL

Boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, in British and American shipbuilding traditions the construction is dated from this event, with only the ship's launching considered more significant in its creation.

Structural keels

Keel laid for the USS United States in drydock

A structural keel is a large beam around which the hull of a ship is built. The keel runs in the middle of the ship, from the bow to the stern, and serves as the foundation or spine of the structure, providing the major source of structural strength of the hull. The keel is generally the first part of a ship's hull to be constructed, and laying the keel, or placing the keel in the cradle in which the ship will be built, is often a momentous event in a ship's construction — so much so that the event is often marked with a ceremony, and the term lay the keel has entered the language as a phrase meaning the beginning of any significant undertaking. Modern ships are now largely built in a series of pre-fabricated, complete hull sections rather than being built around a single keel, so the start of the shipbuilding process is now considered to be when the first sheet of steel is cut.

The keel converts sideways force into a forward force.

The keel contributes substantially to the longitudinal strength and effectively local loading caused when docking the ship. The most common type of keel is the "flat plate keel", and this is fitted in the majority of ocean-going ships and other vessels. A form of keel found on smaller vessels is the "bar keel", which may be fitted in trawlers, tugs, and smaller ferries. Where grounding is possible, this type of keel is suitable with its massive scantlings, but there is always a problem of the increased draft with no additional cargo capacity. If a double bottom is fitted, the keel is almost inevitably of the flat plate type, bar keels often being associated with open floors, where the plate keel may also be fitted.

Duct keels are provided in the bottom of some vessels. These run from the forward engine room bulkhead to the collision bulkhead and are utilized to carry the double bottom piping. The piping is then accessible when cargo is loaded.

If a ship suffers severe structural stress — classically during a shipwreck when running aground in a heavy sea — it is possible for the keel to break or be strained to the extent that it loses structural integrity. In this case the ship is commonly said to have "broken its back". Such a failure means that the entire structure of the ship and its machinery has been compromised and repairing such damage would require virtually re-building the ship from the ground up. A ship that has broken its back is almost certainly unsalvagable and subsequently written off by its insurers.

Hydrodynamic keels

Keels provide extra stability by providing a weight low enough to significantly lower the centre of gravity.

Non-sailing keels

The keel surface on the bottom of the hull gives the ship greater directional control and stability. In non-sailing hulls, the keel helps the hull to move forward, rather than slipping to the side. In traditional boat building, this is provided by the structural keel, which projects from the bottom of the hull along most or all of its length. In modern construction the bar keel or flat-plate keel performs the same function. There are many types of fixed keels, including full keels, long keels, fin keels, winged keels, bulb keels, and bilge keels among other designs. Deep draft ships will typically have a flat bottom and employ only bilge keels, both to aid directional control and to damp rolling motions.

Sailboat keels

In sailboats, keels use the forward motion of the boat to generate lift to counter act the leeward force of the wind. The rudimentary purpose of the keel is to convert the sideways motion of the wind when it is abeam into forward motion. A secondary purpose of the keel is to provide ballast.

Capsizing effect of a sailing keel

Keels are different from centreboards and other types of foils in that keels are made of heavy materials to provide ballast to stabilize the boat. Keels may be fixed, or non-movable, or they may retract to allow sailing in shallower waters. Retracting keels may pivot (a swing keel) or slide upwards to retract, and are usually retracted with a winch due to the weight of the ballast. Since the keel provides far more stability when lowered than when retracted (due to the greater moment arm involved), the amount of sail carried is generally reduced when sailing with the keel retracted.

Types of non-fixed keels include swing keels and canting keels. Canting keels can be found on racing yachts, such as those competing in the Volvo Ocean Race. They provide considerably more righting moment as the keel moves out to the windward-side of the boat while using less weight. The horizontal distance from the weight to the pivot is increased, which generates a larger righting moment.

Etymology

The word "keel" comes from Old English cēol, Old Norse kjóll, = "ship" or "keel". It has the distinction of being regarded by some scholars as the very first word in the English language recorded in writing, having been recorded by Gildas in his 6th century Latin work De Excidio et Conquestu Britanniae, under the spelling cyulae (he was referring to the three ships that the Saxons first arrived in).[1][2]

Carina is the Latin word for "keel" and is the origin of the term careen (to clean a keel and the hull in general, often by rolling the ship on its side). An example of this use is Careening Cove, a suburb of Sydney, Australia, where careening was carried out in early colonial days.

The part of a ship

anchor ancla

ballast lastre

berth litera

bill of lading lista de artículos transportados

boat bote

bow proa

bulkhead mamparo

bulwark bastión

bunk litera, camastro

cabin camarote

cockpit cabina

cordage soga, cuerda

crow's nest canasta en lo alto del mástil

deck cubierta

dinghy bote

ensign insignia

figurehead mascarón de proa

hatch escotilla

helm timón

hoot toque de sirena

hull casco

jib foque

keel quilla

life belt (US) salvavidas

life buoy (GB) salvavidas

life jacket (GB) chaleco salvavidas

life vest (US) chaleco salvavidas

log book diario de a bordo

mast mástil

oar remo

outboard motor motor fuera de borda

periscope periscopio

poop popa

port babor

promenade deck cubierta de paseo

propeller hélice

prow proa

raft balsa

rig aparejo

rowboat (US) bote de remos

rowing boat (GB) bote de remos

rubber dinghy bote neumático

rudder timón

sail vela

sonar sonar

spar palo, poste

starboard estribor

stern popa

tiller

caña del timón

THE PARTS OF A SHIP

The parts of a ship vary, depending on what kind of ship it is, but a few general parts are common to all ships. Knowing the parts of a ship will increase your understanding when reading about boating related topics, and will also help you orient yourself when on board a ship. Many of the terms used to describe parts of ships are very old, as humans have been building, sailing, and talking about ocean going vessels for thousands of years.

The core of a ship is the structural keel, a heavily reinforced spine which runs along the bottom of the ship, in the middle. The keel supports the structure of the ship, and is the first part of the ship to be built, since it serves as a foundation. Some ships also have a hydrodynamic keel designed to increase their performance efficiency, which takes the form of a streamlined projection from the bottom of the ship to help it move quickly and smoothly through the water. The framework for the hull or shell, the body of the ship, is attached to the keel.

The hull is the most visible part of a ship, because it is the body of the watercraft. The hull makes the ship buoyant while providing shelter to those on board, and is divided by bulkheads and decks, depending on the size of the ship. Bulkheads are compartments which run across the ship from side to side, creating isolated areas in the ship, while decks are analogous to the floors of a house. A small ship may only have one primary deck, while larger ones may have over 10 decks, stacked from top to bottom.

The very bottom of a ship is known as the bilge, and the top is usually called the top deck. The top deck is broken up by the bridge, a covered room which serves as the command center for the ship. On larger ships, the top deck may have several levels, designed to isolate various types of the ship. A larger ship may also have several deck areas topside, including the poop deck, the deck in the rear of the ship, and the afterdeck, located directly behind the bridge. The rig, including masts, rigging, and sails, rises up from the top deck.

The front region of a ship is called the bow, and the rear is the stern. When someone is fore, they are in the front of the boat, while a sailor located amidships would be in the middle of the ship, and a person to the rear of the ship is aft. The right hand side of a ship is starboard, and the left is port.

REPUBLICA BOLIVARIANA DE VENEZUELAMINISTERIO DEL PODER POPULAR PARA LA DEFENSA

UNIVERSIDAD EXPERIMENTAL DE LAS FUERZAS ARMADASUNEFA PUERTO CABELLO EDO CARABOBO

HANDOUT N º 1

Prefixes and Suffixes in EnglishJill Kerper Mora

San Diego State University

Of the twenty thousand most commonly used words in English, four thousand--or 20 percent--have prefixes. Fifteen prefixes make up 82 percent of the total usage of all prefixes. They are listed below.

ab (from)--abnormal ex (out)--extractad (to)--adhesion in, il, un, ir (not)--inadequatebe (by)--belittle pre (before)--predictcom, con, co, col (with)--conjunction pro (in front of)--proceedde (from)--decentralize re (back)--rebuttaldis, di (apart)--dissect sub (under)--subwayen (in)--enact un (not)--unannounced

Other common prefixes and their meanings include:

ante (before)--antedate non (not)--non-unionanti (against)--antidote out (beyond)--outweighauto (self)--autobiography peri (around)--perimeterbi (two)--bisect poly (many)--polygonbene (well)--benefactor post (after)--postscriptcircum (around)--circumnavigate retro (backwards)--retrogressivecontra (against)--contradict semi (half)--semicircleequi (equal)--equilateral super (above)--superimposefore (before)--forewarn syn, sym (with)--synthesisinter (between)--international trans (across)--transformmono (one)--monologue tele (afar)--telescope

Common suffixes and their functions are listed below. The most common suffixes are starred.

Noun Suffixes

-ness* (state of being)--arbitrariness-ment* (agency or instrument)--government-ance* (quality, state of being)--disturbance-tion* (state of being)--irrigation-ant* (person or thing acting as agent)--descendant-ion (results of)--fusion

-sion (the act, quality, result of)--explosion-ation (the act of)--formation-ity or -ty (state or condition)--electricity, unity-ence (quality, state of being)--congruence-hood (condition, state of being)--neighborhood-ship (condition, state of being)--hardship-or (state, quality, agent, doer)--elector-ism (state of being)--nationalism-ist (state, agent, doer)--scientist

Adjective Suffixes

-able* or -ible* (capacity, fitness, tending to, able to)--serviceable, divisible-al* or -ial* (belonging to, pertaining to)--coastal, remedial-ful* (full of)--fearful-ive* (having nature or quality of)--productive-ous* (abounding in, having)--mountainous-ic (of, relating to)--volcanic-ish (of the nature of)--mannish-less (without, free from)--selfless-ary (pertaining to, place for)--tributary

Verb Suffixes

-ize (to acquire, become like)--Americanize-fy (to make, add to, form into)--magnify-ate (acted upon, function, affected)--emancipate-en (made of or belonging, cause to be)--soften

Adverb Suffixes

-ly (in manner of)--rapidly-wise (with regard or respect to)--lengthwise-ways (course, direction, manner)--sideways-ward (toward, position)--southward

The most important affixes and roots for the content area teacher to consider are those that are important to the particular subject. For example, a science instructor might find the following affixes occurring commonly in the reading material:

homo- (same or like)--homogeneous pro- (forth)--progenitorhetero- (other or different)--heterogeneous inter- (between or among)--intercellularhydro- (water)--hydrocarbon bi- (two)--bipedequi- (equal)--equidistant -ology (study of)--biology

aqua- (water)--aqualung -ism (state of condition)--alcoholism

A mathematics instructor might well find the following list of affixes more appropriate to develop:

hemi-, demi- (half--hemisphere, demitasseuni-, mono- (one)--unitary, monologuebi-(two)--bisecttri- (three)--trianglequadri-, tetra- (four)--quadrilateral, tetrameterpenta-, quin- (five)--pentagon, quintethex-, hexa- (six)--hexagonalsept-, hepta- (seven)--septuagenarian, heptameterocta- (eight)--octagonnona- (nine)--nonarydec- (ten)--decadecenti- (hundred)—centimeter

THE SUFFIXES IN ENGINEERING

A

a-, an- = not, without [anhydrous, amorphous, atrophy]

acid = sour, sharp [hydrochloric acid, sulfuric acid]

alkali = soda ash, [alkali, alkaline]

allo, -io = other, different [allotrope, alloy]

alpha = 1st letter of Greek alphabet [alpha particle, alpha rays]

amin = ammonia amine [amino acid, ammonia, amine]

amph, -i, -o = double, on both sides [amphoteric, amphibian]

-ane = single covalent bond [alkane, hexane, butane, propane]

anti = against, opposite [antiseptic, antibiotic]

-ate = used to indicate a salt of an acid ending in -ic [sulfate, nitrate]

aqua = water [aqueous, aquatic, aquamarine]

B

baro = pressure [barometer, barometric]

beta = second letter of Greek alphabet [beta particle, beta rays]

bi = two [binary, bipolar]

bio = life [biology, biochemistry, biometrics]

C

carb, -o, -on = coal, carbon [carbohydrate, carbonic, carbon dioxide]

chem = chemistry, chemical [chemical, chemotherapy]

co, -l, m, -n = with, together [covalent, coefficient, colligative, concuction]

com = with, together [composition, combination]

conjug = joined together [conjugate acid, conjugal acid]

cosm,-o = the world or universe [cosmic rays, cosmology]

cry, -mo, -o = cold crystal [cryogenics]

D

de = down, without, from [decomposition, denatured, dehydrated]

dens = thick, dense [dense, density]

di = separate, double, across [diatomic, divalent, disaccharide]

dis = separate, apart [dissociation, dissolved]

duc, -t = lead [ductile, induction]

E

e = out, without, from [evaporation, eradication]

ef = out, from, away [effervescence, effluent]

electr, -i, -o = electrode, electric [electrolyte, electrochemical, electrical, electromechanical]

elem = basic [elements, elementary]

empir, -o = experienced [empirical formula]

en = in, into [endothermic, endocrine]

-ene = double covalent [alkene, acetylene, toluene, propylene]

equ = equal [equilibrium, equivalent]

erg = work, energy [erg, energy, ergonomic]

exo = out, outside, without [exothermic, exocrine, exothermal]

F

ferr, -o = iron [ferromagnetism, ferric, ferrous]

fiss, -i, -ur = cleft, split [fission, fissure]

flu = flow [fluids, confluent]

fract = break, broken [fraction, refraction, fracture]

G

gamma = 3rd letter of Greek alphabet [gamma rays, gamma]

gen = bear, produce, beginning [gene, genetic]

glyc, -er, -o = sweet [glycogen, glycolysis, glycose, glycolipid, glycol, glycerine]

graph, -o, -y = write, writing [graphite, graphical, graphics]

H

halo- = salt [halogens]

hetero- = other, different [heterogeneous]

hom, eo, -o = same, alike [homogeneous]

hybrid = combination [hybrid orbital]

hydr, -a, -i, -o = water [hydrolysis, hydroelectric]

hyper = over, above, excessive [(hy)perchloric acid, hyperactive, hypertension]

hypo = under, beneath [hypochlorous acid, hypothetical, hypothermic]

I

-ic = show the higher of two valences, having some characteristics of [ferric, metallic]

-ide = group of related chemical compounds [monosaccharide]; binary compound [sodium chloride, hydrogen cyanide]; chemical element with properties similar to another [lanthanide series]

im = not [immiscible, impenetrable]

in = in, into [intrinsic, internal]

-ine = of or pertaining to, of the nature of, made of, like [crystalline, marine]; halogen [bromine]; basic compound [amine]; alkaloid [quinine]; amino acid [glycine]; mixture of compounds [gasoline]; commercial material [glassine]

-ion = process [fusion, fission, evaporation]

iso = equal [isomers, isometric, isochoric]

-ite = salt or ester of an acid named with an adjective ending in -ous [sulfite]; rock, mineral [graphite]; fossil [trilobite]; product [metabolite]; commercial product [ebonite]

K

kilo = thousand [kilogram, kilojoule]

kine = move, moving, movement [kinetic energy]

L

lip, -o = fat [lipoprotein, lipid]

liqu, -e, -i = fluid, liquid [liquefy, liquor]

lys, -io, -is, -io = loose, loosening, breaking [hydrolysis]

M

macr, -o = large, long [macromolecule, macroscopic]

malle, -o, -us = hammer [malleable, malleability]

mer, -e, -i, -o = part [dimer, polymer, isomer]

met, -a = between [metabolism, metamorphosis]

-meter = measure [calorimeter, thermometer]

mill -e, -i, -o = one thousand [milliliter, milligram, millimeter]

misc = mix [miscible, miscellaneous]

mon -a, -er, -o = single, one [monomer, monovalent, monoxide]

morph, -a, -o = form [amorphous, metamorphic, polymorphic]

N

neo = new [neoprene]

neutr = neither [neutral, neutron]

nom, -en, -in = name [nominal, nomenclature]

non = not, ninth [nonpolar, non-reactive]

nuc, -ell, -i = nut, center [nucleus, nuclear]

O

oct, -i, -o = eight [octet, octane]

-oid = like, form [metalloid, colloid]

orbi, -t = circle [orbital, orbit]

-ous = possessing, full of, lower of two possible valences [aqueous, porous, ferrous, ferrous sulfide]

oxid = oxygen [oxide, oxidation]

P

photo = light [photochemical, photosynthesis]

polar, -i = of the pole [polarity, polar]

poly = many [polymer]

pro = forward, positive, for, in front of [proton, projectile, projection]

Q

quant = how much [quantum, quanta, quantity]

R

radi, -a, -o = spoke, ray [radius, radioactive, radial, radiation]

S

sacchar, -o = sugar [monosaccharide, saccharine]

sal, -i = salt [salinity, saline]

solu- = dissolve [solubility, soluble, solution]

spect = see, look [spectator, speculate, spectacle]

super = above, over [superheated, supersonic]

syn = together, with [photosynthesis, synthetic]

T

therm, -o = heat [thermodynamics, thermochemistry, thermal conductivity]

thesis = arranging, statement [hypothesis, antithesis]

tran, -s = across, through [transition, transfer, transfusion]

U

un = not [unsaturated, unstable]

V

PREFIJOSSe emplean antes de las raíces o derivados modificando su significado, como:

con-vertin-vert

per-vertad-vert

re-vertsub-vert

1. Prefijos Sajones

SIGNIFICA ... COMO EN ...

a in, to, on afield (muy lejos), afloat (a flote)

be intensity bespoke (encargar), besmear (ensuciar)

en to determine enable (habilitar)

em to determine embitter (amargar)

for negation forbid (prohibir), forbear (reprimir)

fore before foretell (predecir), foretaste (saborear de antemano)

mis error mistake (equivocación), misconduct (mala conducta)

n not never (nunca), non (no), nor (ni), naught (cero)

over above overdone (recocido)

to this today (hoy), tonight (esta noche)

un not undone (sin terminar), unfit (incompetente)

under beneath underdone (crudo)

up upwards upturn (alza)

with against, away  withstand (resistir), withhold (retener)

2. Prefijos Griegos

SIGNIFICA ... COMO EN ...

a, an not apathy (apatía), anarchy (anarquía)

amphi both amphibious (anfibio)

ana through analogy (analogía)

anti against antipodes (antípodas), antipathy (antipatía)

apo from apostle (apóstol)

cata down cataract (catarata)

dia through diameter (diámetro)

en in endemic (endémico)

em in emphasis (énfasis)

epi upon epitaph (epitafio)

ex out exodus (éxodo)

hyper over hypercritical (hipercrítico)

hypo under hypocritical (hipócrita)

meta change  metamorphosis (metamorfosis)

para beside paragraph (párrafo)

peri around perimeter (perímetro)

syl with syllabe (sílaba)

sym with sympathy (afinidad, empatía)

syn with syntax (sintaxis, resumen)

 

3. Prefijos Latinos

SIGNIFICA ... COMO EN ...

a, ab, abs from, away avert (separar), abhor (detestar)

ad (ac, af, al, an) to adhere (adherirse), accede (acceder), affix (anexar)

ante before antedate (anticipar)

bi, bis two biped (bípedo), bissextile (bisiesto)

circum, circu about, around circumference (circunferencia),circulate (circular)

con (co, cog, col, com, cor)

with conjoin (asociar), cognate (pariente), collect (congregar), colligate (juntar) 

contra (counter) against contradict (contradecir), counteract (contrariar)

de down descend (bajar)

dis (di, dif) asunder (en 2) dislodge (desalojar), divide (separar)

e (ex, ef) out of eject (arrojar), exit (salir), effect (ejecutar)

extra beyond extravagant (extravagante)

ig in ignoble (indigno, humilde)

im in immoral (inmoral), immense (inmenso)

in (con verbo) in, into intomb (sepultar), invade (invadir)

in (con adjetivo) not  incorrect (incorrecto)

inter between intercede (interceder)

intro within introduce (presentar una persona a otra)

ob (oc, of, op) against obstruct (obstruir), occurrence (incidente), oppose (oponerse)

per through perspire (transpirar)

post after postscript (postdata)

prae (pre) before preordain (predestinar)

pro forth project (proyecto)

praeter (preter) beside, past pretermission (omisión)

re back, again remit (condonar)

retro backwards retrogression (regresión)

se aside select (seleccionar)

sub (suc, suf, sur, su)

under subject (sujeto), succumb (sucumbir),suffer (sufrir), surrender (rendirse)

subter underneath subterfuge (evasiva, subterfugio)

super upon, above  superfluous (superfluo)

trans (tra) across transmit (trasmitir)

ultra beyond  ultramarine (ultramar)

vapor, -i = steam, vapor [vaporization, vaporizer, vapor pressure]

vulcan = fire [vulcanized, vulcanization]

Y

-yl = wood, matter; organic acid radical [carbonyl]; chemical names of organic compounds when they are radicals [alkyl, ethyl, phenyl]

-yne = triple covalent bond [alkyne, ethyne

Preparation for an American University ProgramVocabulary Workshop

 Suffixes

Suffixes are groups of letters attached to the ends of roots, words, and word groups. Suffixes serve a grammatical function. A suffix can indicate what part of speech (noun, verb, adjective, adverb) to which the word belongs. Suffixes can also modify and extend meaning. The following suffixes are grouped beneath the grammatical function they perform.

NOUNS

Nouns perform the function of naming. Nouns name persons, places animals or things, as well as groups, ideas and qualities. In a sentence, nouns can be subjects, objects, or appositives.

-acy, -cyo Noun: state or quality

privacy: the state of being alone priv + acy

infancy: the state of being a baby or young child in  + fan + cy

-ageo Noun: activity, or result of action

courage : having the spirit to overcome fear cour + age

-alo Noun: action, result of action

referral : the action of directing a person to another place, person or thing re  + ferr + al

-ano Noun: person

artisan : a craftsperson arti + san

-ance, -enceo Noun: action, state, quality or process

resistance : the action of opposing something re  + sist + ance

independence: the state of not being under the control of others, free, self-governing

in  + de + pend + ence

-ancy, -encyo Noun: state, quality or capacity

vacancy : an empty room or position vac  + ancy

agency: the capacity to exert power or influence, a position or person that performs a function

ag  + ency

-ant, -ento Noun: an agent, something that performs the action

disinfectant : an agent that destroys germs, somthing that cleans

dis  + in + fect + ant dependent: a thing supported by another, a thing determined by another

de  + pend + ent

-ateo Noun: state, office, fuction

candidate : a person nominated for an office or position candid + ate

-ationo Noun: action, resulting state

specialization : the result of being distinguished by one quality or ability spec  + ial + iz + ation

-domo Noun: place, state of being

wisdom : possessing knowledge wis + dom

-er, -oro Noun: person or thing that does something

porter : a person who carries things port  + er

collector: a person who collects or gathers things col  + lect + or

-fulo Noun: an amount or quanity that fills

mouthful : an amount that fills the mouth mouth + ful

-ian, ano Noun: related to, one that is

pedestrian : a person who walks ped  + estr + ian

human: a person hum + an

-iao Noun: names, diseases

phobia : an illogical fear of something phob + ia

-iatryo Noun: art of healing

psychiatry : branch of medicine that deals with the mind and emotions psych  + iatry

-ic, icso Noun: related to the arts and sciences

arithmetic : a branch of math that usually deals with non-negative numbers arithm + et + ic

economics: the social science related to studying business eco + nom + ics

-iceo Noun: act

malice : the desire to do evil mal  + ice

-ingo Noun: material made for, activity, result of an activity

flooring : a material made for floors floor + ing

swimming: the activity of swimming or moving through water swim(m) + ing

building: the result of making a structure build + ing

-iono Noun: condition or action

abduction : the action of carrying someone away by force ab  + duct + ion

-ismo Noun: doctrine, belief, action or conduct

formalism : a belief in sticking to prescribed forms or artistic styles form  + al + ism

-isto Noun: person or member

podiatrist : a foot doctor pod  + iatr + ist

-iteo Noun: product or part

graphite : a black material used in making pencils graph  + ite

-ity, tyo Noun: state or quality

lucidity : clear thinking luc  + id + ity

novelty: something new or unusual nov  + el + ty

-iveo Noun: condition

native : a person born in a specific place nat  + ive

-mento Noun: condition or result

document : an official paper usually showinf proof or evidence of something doc u + ment

-nesso Noun: state, condition, quality

kindness : the quality of being kind or nice

kind + ness

-oro Noun: condition or activity

valor : bravery, courage val + or

-oryo Noun: place for, serves for

territory : an area around a place territ  + ory

-shipo Noun: status, condition

relationship : the state of being related or connected to something or someone re  + lat + ion + ship

-ureo Noun: act, condition, process, function

exposure : the condition of being exposed or unprotected pos  + ure

-yo Noun: state, condition, result of an activity

society : companionship soci  + et + y

victory: the result of winning something vict + or + y

VERBSVerbs make statements about nouns, ask questions, give commands, or show states of being. Verbs can be active or passive. Verbs also show tense or time of action.

-ateo Verb: cause to be

graduate : to give a degree to, to pass from one stage to the next grad u + ate

-edo Verb: past tense

attained : something that has been reached or grasped at  + tain + ed

-eno Verb: to cause to become

moisten : to cause to become moist or damp moist + en

-er, -oro Verb: action

ponder : to think about pond  + er

clamor: to make noise, to call for loudly clam  + or

-ifyo Verb: cause

specify : to name or indicate in detail spec  + ify

-ingo Verb: present participle

depicting : showing, describing with images or pictures de  + pict + ing

-izeo Verb: cause

fantasize : to dream about something, to create images in the mind fant  + as + ize

-ureo act

Verb: conjecture : to come to a conclusion by supposition or guesswork con  + ject + ure

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ADJECTIVESAdjectives describe or modify nouns. Adjectives tell the reader more about the noun used in the sentence.

-able, -ibleo Adjective: worth, ability

solvable : able to be solved or explained solv  + able

incredible: not able to be believed, amazing in  + cred + ible

-al, -ial, -icalo Adjective: quality, relation

structural : related to the physical make up of a thing struct  + ure + al

territorial: related to nearby or local areas territ  + or + ial

categorical: related to a category, aboslute cate  + gor + ical

-ant, -ent, -iento Adjective: kind of agent, indication

important : marked by worth im  + port + ant

dependent: determined or relying upon something else de  + pend + ent

convenient: at hand, easy to use con  + ven + ient

-ar, -aryo Adjective: resembling, related to

spectacular : related to something that is eye-catching or amazing spectac  + ul + ar

unitary : related to units or single groups representing quantities unit  + ary

-ateo Adjective: kind of state

inviolate : not disturbed, pure in  + viol + ate

-edo Adjective: having the quality of

terraced : having terraces or steps terra c + ed

-eno Adjective: material

silken : made from silk, a fiber produced by worms silk + en

-ero Adjective: comparative

brighter : more light bright + er

-esto Adjective: superlative

strongest : having the most strength strong + est

-fulo Adjective: having, giving, marked by

fanciful : marked by imagination fanc i + ful

-ico Adjective: quality, relation

generic : related to a whole group gener  + ic

-ileo Adjective: having the qualities of

projectile : something thrown with an outside force pro  + ject + ile

-ingo Adjective: activity

cohering : the act of sticking together co  + her + ing

-ish

o Adjective: having the character of newish : modern, recent

new + ish

-ive, -ative, -itiveo Adjective: having the quality of

festive : having the quality of a festival or party fest + ive

cooperative : being able or willing to work with another person or thing co  + oper + ative

sensitive: easily felt, responsive to the senses sens  + itive

-lesso Adjective: without, missing

motiveless : a reason for someone to do something mot  + ive + less

-ous, -eous, -ose, -iouso Adjective: having the quality of, relating to

adventurous : charcterized by the desire to seek new experiences or risks ad  + vent + ur + ous

courageous : characterized by courage, brave cour + ag + eous

verbose: having more words than needed verb  + ose

fractious: characterized by being difficult or troublesome fract  + ious

-yo Adjective: marked by, having

hungry : having hunger, marked by a desire hungr + y

Back to Vocabulary Workshop Home Page, vocabulary, prefixes, or suffixes.

ADVERBSAdverbs describe verbs, adjectives and other adverbs.

INDEX: F L W

-foldo Adverb: in a manner of, marked by

fourfold : being four times as great four + fold

-lyo Adverb: in the manner of

fluently : marked by ease of movement, effortlessly smooth flu  + ent + ly

-wardo Adverb: in a direction or manner

homeward : toward home home + ward

-wiseo Adverb: in the manner of, with regard to

timewise : with regard to time time + wise

REPUBLICA BOLIVARIANA DE VENEZUELAMINISTERIO DEL PODER POPULAR PARA LA DEFENSA

UNIVERSIDAD EXPERIMENTAL DE LAS FUERZAS ARMADASUNEFA PUERTO CABELLO EDO CARABOBO

ENGLISH IIGUIDE ON PASSIVE VOICE

- La voz pasiva se forma con el verbo TO BE en el mismo tiempo verbal que el verbo activo + el participio del verbo. They produced a lot of wine in Spain. (Ellos producen mucho vino en España).VOZ ACTIVA.A lot of wine is produced in Spain. (Se produce mucho vino en España).VOZ PASIVA.Importante tener en cuenta que la traducción al español se hace con el pronombre reflexivo SE que en inglés no existe.

Las construcciones impersonales (se dice, se comenta, etc.) son muy típicas de la pasiva y difíciles de traducir para los hispanoparlantes. Este tipo de construcción pasiva -utilizada cada vez con mayor frecuencia en los medios- se forma con la estructura sujeto + to be + participle: It is reported (Se informa); It is said (Se dice); It is known (Se sabe); It is supposed (Se supone); It is considered (Se considera); It is expected (Se espera). Veamos algunos ejemplos:ACTIVE: Everybody thinks Cathy works very hard.(Todo el mundo piensa que Cathy trabaja muy duro). PASSIVE 1: Cathy is thought to work very hard. (Se piensa que Cathy...)PASSIVE 2: It is thought that Cathy works very hard. (Se piensa que Cathy...)

1. Present The car is washed ( se lava)The car is being washed

2. Present Continuos The car is being washed ( se está lavand

  3 Present perfectThe car has been washed ( se ha lavado)T4.- Present Perfect ContinuosThe car has been being Washed ( se ha estado lavando )

    5.- Past The car was washed (se lavó)The car was being washed

    6.- . Past Continuos The car was being washed ( se estaba lavando )7.- Past Perfect:The car had been washed ( se habia lavado)8.- Past perfect ContinuosThe car had been being washed( se habia estado lavando)The car had been being washed

    9.- Simple . Future The car will be washed ( se lavará)10.- Future ContinuosThe car will be being washed ( se estará lavando)

    11.-. Future perfect The car will have been washed ( se habrá lavado)12.- Future Perfect Continuos The car will have been being washed ( se habrá estado lavando)

13. ConditionalThe car would be washed (seria lavado)

14.- Conditional perfectThe car would have been washed (habría sido lavado)

15. ModalsThe car (can, could, ...) be washedThe car (can, could, ...) be being washed

16.- Modals + haveThe car (can, could, ...) have been washedThe car (can, ...) have been being washed

What has been done? - ¿Qué se ha hecho?

A house has been built. Se ha construido una casa / Una casa ha sido construida

The whole city has been destroyed by the earthquake.La ciudad entera has sido destruída por el terremoto.

I can't get in. These doors have been locked!No puedo entrar. Estas puertas han sido cerradas con llave!

Those windows have not been closed yet.Aquellas ventanas no han sido cerradas aún.

This wooden floor has not been waxed.Este suelo de madera no ha sido encerado.

Has uncle John been promoted to president of the company?¿El tío John ha sido ascendido a presidente de la empresa?

Have the same mistakes been made before?¿Han sido cometidos los mismos errores antes?

People have been requested to cancel appointments before Monday.Se le ha solicitado a la gente que cancele las citas antes del lunes.

Guess what,... Jack has been taught to drive a car!Adivina qué,... Le han enseñado a Jack conducir un coche!

What has been being done? - ¿Qué se ha estado haciendo?

A house has been being built.

Se ha estado construyendo una casa / Una casa ha estado siendo construida

My mother has been being treated by the same doctors for years.My madre ha estado siendo tratada por los mismos médicos durante años.

Stricter and stricter measures have been being taken to reduce crime in the city. han estado tomando medidas cada vez más estrictas para reducir el delito en la ciudad.

What Is the Passive Construction?

Many verbs have a passive form. The passive construction inverts the active word order to emphasize what happened, rather than who did it:

Active: I repaired the computer.

Passive: The computer was repaired by me.

Notice three things about this transformation of active order into passive order:

1. The object of the active sentence —"the computer"— becomes the subject of the passive sentence. 2. The passive verb has two parts: a form of the verb "be" ("was") and the past participle of the main verb ("repaired"). Other

forms of the verb "be" include these: am, is, are, were, have been, had been, will have been. Other examples of past participles (which are not the same as the past tense, even when they look the same!) include "seen," "shown," and "swum."

3. The actor is now part of a prepositional phrase ("by me"). Passive constructions let you omit the actor altogether:

When Is It All Right to Be Passive?

When You Want to Emphasize Results

Despite the admonitions of grammar checkers, the passive construction has a legitimate function. When you want to emphasize results, use the passive. Consider this statement, written three ways. Which is preferable?

Active: Our clients followed our advice.[The emphasis falls on "our clients."]

Passive:Our advice was followed by our clients.Our advice was followed.[The emphasis falls on "our advice."]

None of these is inherently better than the others: It depends on what you wish to emphasize.

 

When the Sentence Does Not Need an Actor

Sometimes the active construction is easier to understand. But sometimes the passive construction is the clearest way to express your meaning. You must choose the construction that best says what you mean. On these occasions the passive construction is a better choice:

When the actor is not important ("The solution was heated to 100º"). When the actor is unknown ("The jewelry has been stolen"). When you do not wish to name the actor ("One thousand dollars has been contributed").

 

When Is the Passive the Wrong Choice?

The passive construction will be confusing or wordy in these situations:

1. When you write instructions.

2. When "it" is the subject of the passive verb

 

1. When you write instructions

Write instructions with active or imperative verbs — never with passive verbs. Instructions must focus on the action. Instructions must also indicate the actor. Passive constructions frequently omit the actor so the reader cannot tell who should be doing what. Passive

verbs use the past participle and thus cannot direct action. Because of these intrinsic features, the passive construction produces vague and confusing instructions:

Passive:

It should be noted that any change to the procedure must be recorded in the master file.

Active/ Imperative:

Note: When you change the procedure, record the change in the master file.  

Passive:

Static-sensitive components are stored in protective enclosures.

Active/ Imperative:

Store static-sensitive components in protective enclosures.

Passive:

The form must be signed by the employee to authorize release of physician information to the insurance company.

Active:

The employee must sign the form to authorize release of physician information to the insurance company.

Imperative:

Sign the form to authorize release of physician information to the insurance company.

 

2. When "it" is the subject of the passive verb

Delete "it should be noted that," "it is expected that," "it is recommended that," "it may be observed that," and similar constructions. I have yet to see an instance when a passive construction using "it" as the subject clarifies anything.

Passive:

It should be noted that any modification may seriously impact our present transmission rate and/or our system production.

Active:

Any modification may seriously impact our present transmission rate and/or our system production.

Passive:

It is recommended that this new policy be instituted at once.

Active:

We recommend instituting this new policy at once.

Imperative:

Institute this new policy at once. Passive:

It has been agreed that additional journal and log offloads will be run on production.

Active:

We have agreed to run additional journal and log offloads on production.

Imperative:

Run additional journal and log offloads on production.

Grammar Checker Note: You do not have to live with the default setting on your grammar checker. Most grammar checkers let you select the features ("long sentences," "wordiness," "passive constructions") you wish to note. Many offer a menu of different pre-set styles, from "technical report" to "advertising."

So, if you are writing a report on an experiment, disable the passive voice feature. Conversely, if you are preparing a user's guide or other set of instructions, make sure that feature is turned on.

Qué es la construcción pasiva?

Many verbs have a passive form. Muchos verbos tienen una forma pasiva. The passive construction inverts the active word order to emphasize what happened, rather than who did it: La construcción pasiva invierte el orden de las palabras activa para enfatizar lo que pasó, en lugar de quién lo hizo:

Active: Activo: I repaired the computer.

Passive: Pasivo: The computer was repaired by me. La computadora fue reparada por mí.

Notice three things about this transformation of active order into passive order: Aviso tres cosas acerca de esta transformación del orden activa en orden pasiva:

1. The object of the active sentence —"the computer"— becomes the subject of the passive sentence. El objeto de la oración activa - "el equipo" - se convierte en el sujeto de la oración pasiva.

2. The passive verb has two parts: a form of the verb "be" ("was") and the past participle of the main verb ("repaired"). El verbo pasivo tiene dos partes: una forma del verbo "ser" ("era") y el participio pasado del verbo principal ("reparar"). Other forms of the verb "be" include these: am , is , are , were , have been , had been , will have been . Otras formas del verbo "ser" son los siguientes: de la mañana, es decir, son, fueron, han sido, había sido, habrá sido. Other examples of past participles (which are not the same as the past tense , even when they look the same!) include "seen," "shown," and "swum." Otros ejemplos de participios pasados (que no son los mismos que el tiempo pasado, incluso cuando tienen el mismo aspecto!) incluyen "visto", "muestra", y "nadar".

3. The actor is now part of a prepositional phrase ("by me"). El actor es ahora parte de un sintagma preposicional ("por mí"). Passive constructions let you omit the actor altogether: construcciones pasivas que se omite por completo el actor:

Passive: Pasivo:

The computer was repaired. El equipo fue reparado.

When Is It All Right to Be Passive? Cuando está todo derecho a ser pasiva?

When You Want to Emphasize Results Cuando se quiere enfatizar Resultados

Active: Activo: Our clients followed our advice. Nuestros clientes seguido nuestros consejos. [The emphasis falls on "our clients."] [El énfasis recae en "nuestros clientes".]

Passive: Pasivo: Our advice was followed by our clients. Nuestro consejo fue seguido por nuestros clientes. Our advice was followed. Nuestro consejo fue seguido. [The emphasis falls on "our advice."] [El énfasis recae en "nuestro consejo."]

None of these is inherently better than the others: It depends on what you wish to emphasize. Ninguno de ellos es intrínsecamente mejor que los otros: Depende de lo que usted desea destacar.

When the Sentence Does Not Need an Actor Cuando la Sentencia no necesita un actor

Sometimes the active construction is easier to understand. A veces la construcción activa es más fácil de entender. But sometimes the passive construction is the clearest way to express your meaning. Pero a veces la construcción pasiva es la forma más clara de expresar su significado. You must choose the construction that best says what you mean . Usted debe elegir la construcción que mejor se dice lo que quieres decir. On these occasions the passive construction is a better choice: En estas ocasiones la construcción pasiva es una mejor opción:

When the actor is not important ("The solution was heated to 100º"). Cuando el actor no es importante ("La solución se calienta a 100 º").

When the actor is unknown ("The jewelry has been stolen"). Cuando el actor es desconocido ("La joyería ha sido robado"). When you do not wish to name the actor ("One thousand dollars has been contributed"). Cuando usted no desea que el

nombre del actor ("Mil dólares ha contribuido").

When Is the Passive the Wrong Choice? ¿Cuándo es el pasivo de la decisión equivocada?

The passive construction will be confusing or wordy in these situations: La construcción pasiva ser confuso o muchas palabras en estas situaciones:

1. 1. When you write instructions Al escribir las instrucciones

Write instructions with active or imperative verbs — never with passive verbs. Escriba las instrucciones con verbos activos o imperativo - nunca con los verbos pasivos. Instructions must focus on the action. Las instrucciones deben centrarse en la acción. Instructions must also indicate the actor. Las instrucciones también deben indicar el actor. Passive constructions frequently omit the actor so the reader cannot tell who should be doing what. construcciones pasivas frecuentemente omiten el actor para que el lector no puede saber quién debe hacer qué. Passive verbs use the past participle and thus cannot direct action. verbos pasivos usan el participio pasado y por lo tanto no puede la acción directa. Because of these intrinsic features, the passive construction produces vague and confusing instructions: Debido a estas características intrínsecas, la construcción pasiva produce instrucciones vagas y confusas:

Passive: Pasivo:

It should be noted that any change to the procedure must be recorded in the master file. Cabe señalar que cualquier cambio en el procedimiento deberán estar registrados en el archivo maestro.

Active/ Imperative: Activo / imperativo:

Note: When you change the procedure, record the change in the master file. Nota: Cuando se cambia el procedimiento, registrar el cambio en el archivo maestro.

Passive: Pasivo:

Static-sensitive components are stored in protective enclosures. Sensible a los componentes estáticos se almacenan en cajas de protección.

Active/ Imperative: Activo / imperativo:

Store static-sensitive components in protective enclosures. Tienda componentes sensibles a la estática en los recintos de protección.

Passive: Pasivo:

The form must be signed by the employee to authorize release of physician information to the insurance company. El formulario debe ser firmado por el empleado para autorizar la divulgación de información para el médico de la compañía de seguros.

Active: Activo:

The employee must sign the form to authorize release of physician information to the insurance company. El empleado debe firmar la solicitud para autorizar la divulgación de información para el médico de la compañía de seguros.

Imperative: Imperativo:

Sign the form to authorize release of physician information to the insurance company. Firma el formulario para autorizar la divulgación de información para el médico de la compañía de seguros.

2. 2. When "it" is the subject of the passive verb Cuando "él" es el sujeto del verbo pasivo

Delete "it should be noted that," "it is expected that," "it is recommended that," "it may be observed that," and similar constructions. Eliminar "cabe señalar que," se espera que "," se recomienda que, "" se puede observar que, "y obras similares. I have yet to see an instance when a passive construction using "it" as the subject clarifies anything. Todavía tengo que ver un ejemplo, cuando una construcción pasiva con "se" en el asunto se aclara nada.

Passive: Pasivo:

It should be noted that any modification may seriously impact our present transmission rate and/or our system production. Cabe señalar que cualquier modificación puede ser un grave impacto en nuestra actual tasa de transmisión y / o nuestro sistema de producción.

Active: Activo:

Any modification may seriously impact our present transmission rate and/or our system production. Cualquier modificación puede ser un grave impacto en nuestra actual tasa de transmisión y / o nuestro sistema de producción.

Passive: Pasivo:

It is recommended that this new policy be instituted at once. Se recomienda que esta nueva política se instituyó a la vez.

Active: Activo:

We recommend instituting this new policy at once. Se recomienda instituir esta nueva política a la vez.

Imperative: Imperativo:

Institute this new policy at once. Instituto de esta nueva política a la vez. Passive : Pasivo:

It has been agreed that additional journal and log offloads will be run on production. Se ha acordado que el diario adicional y descarga el registro se llevará a cabo en la producción.

Active: Activo:

We have agreed to run additional journal and log offloads on production. Hemos acordado ejecutar diario adicional y descarga el registro de la producción.

Imperative: Imperativo:

Run additional journal and log offloads on production. Ejecutar adicionales revista y descarga el registro de la producción.

Use passive voice in these 6 situations when you:

1) Want to ignore the agent of action because it does not matter.

Example: "The cover of the Annual Report has been torn." "That street has been renamed."

2) Want to hide the identity of the agent since that knowledge may give rise to an awkward situation or an uncomfortable accusation. Such use softens the severity of the situation by masking the identity of the culprit.

Example: "The wrong wire was connected to the power outlet." "All security cameras have been removed from the most sensitive areas of the nuclear plant."

3) Want to maintain the thematic unity between two consecutive sentences.

Example: "The server is not stable. It can be brought down by a single spike in the system load."

4) Want to emphasize the agent by mentioning it at the end of the sentence:

Example: "The circuit was overheated due to the failure of the 10K resistor."

5) Are not sure who the agent is:

Example: "This project has to be finished by March 5th." "The Documentation Plan has to be approved before we can design the templates."

6) Want to stress an action or an outcome:

Example: "Our research budget has been decimated." "They've been had!" "These reports have been altered."

Aquí hay algunas situaciones en las que es perfectamente correcto utilizar la voz pasiva.

Use passive voice in these 6 situations when you: Usar la voz pasiva en estas seis situaciones en las que:

1) Want to ignore the agent of action because it does not matter. 1) ¿Quieres hacer caso omiso de la agente de la acción porque no tiene importancia.

Example: "The cover of the Annual Report has been torn." Ejemplo: "La portada del informe anual se ha roto." "That street has been renamed." "Esta calle ha cambiado de nombre."

2) Want to hide the identity of the agent since that knowledge may give rise to an awkward situation or an uncomfortable accusation. 2) ¿Quieres ocultar la identidad del agente ya que el conocimiento puede dar lugar a una situación incómoda o una acusación incómodo. Such use softens the severity of the situation by masking the identity of the culprit. Tal uso suaviza la gravedad de la situación por ocultar la identidad del culpable.

Example: "The wrong wire was connected to the power outlet." Ejemplo: "El cable estaba mal conectado a la toma de corriente." "All security cameras have been removed from the most sensitive areas of the nuclear plant." "Todas las cámaras de seguridad han sido retirados de las zonas más sensibles de la planta nuclear."

3) Want to maintain the thematic unity between two consecutive sentences. 3) ¿Quieres mantener la unidad temática entre dos condenas consecutivas.

Example: "The server is not stable. It can be brought down by a single spike in the system load." Ejemplo: "El servidor no es estable, puede ser derribado por un solo punto en la carga del sistema.."

4) Want to emphasize the agent by mentioning it at the end of the sentence: 4) ¿Quieres hacer hincapié en que el agente al mencionar que al final de la frase:

Example: "The circuit was overheated due to the failure of the 10K resistor." Ejemplo: "El circuito estaba sobrecalentado debido a la falta de la resistencia de 10K."

5) Are not sure who the agent is: 5) No Está seguro de que el agente es:

Example: "This project has to be finished by March 5th." Ejemplo: "Este proyecto tiene que estar terminado antes del 5 de marzo." "The Documentation Plan has to be approved before we can design the templates." "El Plan de documentación tiene que ser aprobado antes de que podamos diseñar las plantillas".

6) Want to stress an action or an outcome: 6) ¿Quieres hacer hincapié en una acción o un resultado:

Example: "Our research budget has been decimated." Ejemplo: "Nuestro presupuesto de investigación ha sido diezmada." "They've been had!" "Han sido tenido!" "These reports have been altered." "Estos informes han sido alterados."

OBJECTIVE Nº 2 : PASSIVE VOICE

CARACTERISTICAS

1. Se dice que una oración está en VOZ ACTIVA cuando la significación del verbo es producida por la persona gramatical a quien aquél se refiere:Pedro de Mendoza founded Buenos Aires.(Pedro de Mendoza fundó Buenos Aires).

2. Se dice que una oración está en VOZ PASIVA cuando la significación del verbo es recibida por la persona gramatical a quien aquél se refiere:Buenos Aires was founded by Pedro de Mendoza.(Buenos Aires fue fundada por Pedro de Mendoza).

3. Se forma con el auxiliar del verbo to be y el participio pasado del verbo que se conjuga.

4. El complemento de la oración activa pasa a sujeto de la pasiva. Como en castellano, el sujeto de la activa se puede conservar como sujeto agente.

5. Cuando un verbo tiene dos complementos se pueden hacer dos estructuras de pasiva:a) A book was sent to Tom by Mr. Smith, Un libro fue enviado a Tom por Mr. Smith.b) Tom was sent a book by Mr. Smith (pasiva idiomática). Esta estructura no es posible en castellano. 

MODELO DE VERBO EN VOZ PASIVATO BE SEEN = SER VISTO

PRESENTEI am seen, soy vistoyou are seen, eres vistohe is seen, es vistowe are seen, somos vistosyou are seen, sois vistosthey are seen, son vistos

PRETERITO PERFECTOI have been seen, he sido vistoyou have been seen, has sido vistohe has been seen, ha sido vistowe have been seen, hemos sido vistosyou have been seen, habéis sido vistosthey have been seen, han sido vistos

PASADOI was seen, fui vistoyou were seen, fuiste vistohe was seen, fue vistowe were seen, fuimos vistosyou were seen, fuisteis vistosthey were seen, fueron vistos

FUTUROI shall be seen, seré vistoyou will be seen, serás vistohe will be seen, será vistowe shall be seen, seremos vistosyou will be seen, seréis vistosthey will be seen, serán vistos

PRETERITO PLUSCUAMPERFECTO:  I had been seen, había sido vistoCONDICIONAL:  I should be seen, sería vistoFUTURO PERFECTO:  I shall have been seen, habré sido vistoCONDICIONAL PERFECTO:  I should have been seen, habría sido visto

 

 

VOZ ACTIVA Y PASIVA: REGLAS PRACTICAS EN 4 PASOS.

1. La voz pasiva se forma con el verbo to be conjugado más el participio del verbo principal. En inglés es mucho más frecuente que en español y, normalmente,

aparece cuando no es importante quien realiza una acción sino el hecho en sí. Por eso, no siempre que veamos una pasiva, tenemos que traducirlo literalmente, puesto que en español suena más forzado. Sólo es posible el uso de la voz pasiva con

verbos transitivos (verbos que llevan complemento directo).

VOZ ACTIVATom writes a letterTom is writing a letterTom was writing a letterTom wrote a letterTom has written a letterTom had written a letterTom will write a letterTom is going to write a letterTom can write a letterTom could write a letterTom must write a letterTom may write a letterTom might write a letter

VOZ PASIVAA letter is written by TomA letter is being written by TomA letter was being written by TomA letter was written by TomA letter has been written by TomA letter had been written by TomA letter will be written by TomA letter is going to be written by TomA letter can be written by TomA letter could be written by TomA letter must be written by TomA letter may be written...A letter might be written...

2. El sujeto agente se expresa con by. Sin embargo, en la mayoría de las ocasiones se prescinde del sujeto ya que no nos interesa saber quién exactamente ejecuta la acción. Si una oración activa tiene complemento directo e indirecto, cualquiera de

los dos complementos puede ser sujeto paciente de la pasiva:

ACTIVE: Someone gives me a dogPASSIVE 1: A dog is given to me

PASSIVE 2: I am given a dog (forma pasiva idiomática)

La forma pasiva de doing, seeing, etc es being done, being seen, etc.

ACTIVE: I don't like people telling me what to doPASSIVE: I don't like being told what to do

En ocasiones en las que ocurre algo a veces imprevisto, no planeado o fortuito para la formación de la voz pasiva se prefiere usar get y no be:

get hurt, get annoyed, get divorced, get married, get invited, get bored, get lost

3. Las construcciones impersonales (se dice, se comenta, etc.) son muy típicas de la pasiva y difíciles de traducir para los hispanoparlantes. Este tipo de construcción pasiva -utilizada cada vez con mayor frecuencia en los medios- se forma con la

estructura sujeto + to be + participle: It is reported (Se informa); It is said (Se dice); It is known (Se sabe); It is supposed (Se supone); It is considered (Se

considera); It is expected (Se espera). Veamos algunos ejemplos:

ACTIVE: Everybody thinks Cathy works very hard. PASSIVE 1: Cathy is thought to work very hard. (Se piensa que Cathy...)

PASSIVE 2: It is thought that Cathy works very hard. (Se piensa que Cathy...)

ACTIVE: They believe Tom is wearing a white pullover.PASSIVE 1: Tom is believed to be wearing a white pullover. (Se cree que...)

PASSIVE 2: It is believed that Tom is wearing a white pullover. (Se cree que...)

4. USOS ADICIONALES DE SUPPOSEa) Se usa en afirmativo para acciones que estaban planeadas, que se supone que van

a realizar, u obligaciones que uno debería cumplir.You were supposed to be here at 9:00 am!!

b) Otras veces, el uso de supposed indica que estos planes o obligaciones finalmente no se cumplieron:

The train was supposed to arrive at 5 o'clock. (but it arrived at 8 o'clock)You were supposed to go to the supermarket. (but you didn't go)

c) Por el contrario, en negativo, supposed significa la no conveniencia o prohibición de hacer algo:

You are not supposed to smoke here. (you are not allowed to smoke here)You are not supposed to copy our web files. (you must not copy our web files)

HANDOUT N º 3 SHIP STABILITY AND BUOYANCY (15%) CHAPTER 12

REPUBLICA BOLIVARIANA DE VENEZUELA

MINISTERIO DEL PODER POPULAR PARA LA DEFENSAUNIVERSIDAD EXPERIMENTAL DE LAS FUERZAS ARMADAS

UNEFA PUERTO CABELLO EDO CARABOBO

II CORTE

HANDOUT N º 4

In physics, buoyancy (pronounced / ˈb ɔɪ . ə nsi/ ) is an upward acting force exerted by a fluid, that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the over lying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the column than at the top. This difference in pressure results in a net force that tends to accelerate an object upwards. The magnitude of that force is equal to the difference in the pressure between the top and the bottom of the column, and is also equivalent to the weight of the fluid that would otherwise occupy the column. For this reason, an object whose density is greater than that of the fluid in which it is submerged tends to sink. If the object is either less dense than the liquid or is shaped appropriately (as in a boat), the force can keep the object afloat. This can occur only in a reference frame which either has a gravitational field or is accelerating due to a force other than gravity defining a "downward" direction (that is, a non-inertial reference frame). In a situation of fluid statics, the net upward buoyancy force is equal to the magnitude of the weight of fluid displaced by the body [1] This is the force that enables the object to float.

[edit] Archimedes' principle

Main article: Archimedes' principle

Archimedes' principle is named after Archimedes of Syracuse, who first discovered this law.[2] His treatise, On floating bodies, proposition 5 states:

Any floating object displaces its own weight of fluid.

– Archimedes of Syracuse [3]

For more general objects, floating and sunken, and in gases as well as liquids (i.e. a fluid), Archimedes' principle may be stated thus in terms of forces:

Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.

– Archimedes of Syracuse

with the clarifications that for a sunken object the volume of displaced fluid is the volume of the object, and for a floating object on a liquid, the weight of the displaced liquid is the weight of the object.

More tersely: Buoyancy = weight of displaced fluid.

Archimedes' principle does not consider the surface tension (capillarity) acting on the body.[4]

The weight of the displaced fluid is directly proportional to the volume of the displaced fluid (if the surrounding fluid is of uniform density). In simple terms, the principle states that the buoyant force on an object is going to be equal to the weight of the fluid displaced by the object, or the density of the fluid multiplied by the submerged volume times the gravitational constant, g. Thus, among completely submerged objects with equal masses, objects with greater volume have greater buoyancy.

Suppose a rock's weight is measured as 10 newtons when suspended by a string in a vacuum with gravity acting upon it. Suppose that when the rock is lowered into water, it displaces water of weight 3 newtons. The force it then exerts on the string from which it hangs would be 10 newtons minus the 3 newtons of buoyant force: 10 − 3 = 7 newtons. Buoyancy reduces the apparent weight of objects that have sunk completely to the sea floor. It is generally easier to lift an object up through the water than it is to pull it out of the water.

Assuming Archimedes' principle to be reformulated as follows,

then inserted into the quotient of weights, which has been expanded by the mutual volume

yields the formula below. The density of the immersed object relative to the density of the fluid can easily be calculated without measuring any volumes:

(This formula is used for example in describing the measuring principle of a dasymeter and of hydrostatic weighing.)

Example: If you drop wood into water buoyancy will keep it afloat.

Example: A helium balloon in a moving car. In increasing speed or driving a curve, the air moves in the opposite direction of the car's acceleration. The balloon however, is pushed due to buoyancy "out of the way" by the air, and will actually drift in the same direction as the car's acceleration.

[edit] Forces and equilibrium

This is the equation to calculate the pressure inside a fluid in equilibrium. The corresponding equilibrium equation is:

where f is the force density exerted by some outer field on the fluid, and σ is the stress tensor. In this case the stress tensor is proportional to the identity tensor:

Here is the Kronecker delta. Using this the above equation becomes:

Assuming the outer force field is conservative, that is it can be written as the negative gradient of some scalar valued function:

Then:

Therefore, the shape of the open surface of a fluid equals the equipotential plane of the applied outer conservative force field. Let the z-axis point downward. In this case the field is gravity, so Φ = −ρfgz where g is the gravitational acceleration, ρf is the mass density of the fluid. Taking the pressure as zero at the surface, where z is zero, the constant will be zero, so the pressure inside the fluid, when it is subject to gravity, is

So pressure increases with depth below the surface of a liquid, as z denotes the distance from the surface of the liquid into it. Any object with a non-zero vertical depth will have different pressures on its top and bottom, with the pressure on the bottom being greater. This difference in pressure causes the upward buoyancy forces.

The buoyant force exerted on a body can now be calculated easily, since the internal pressure of the fluid is known. The force exerted on the body can be calculated by integrating the stress tensor over the surface of the body which is in contact with the fluid:

The surface integral can be transformed into a volume integral with the help of the Gauss divergence theorem:

where V is the measure of the volume in contact with the fluid, that is the volume of the submerged part of the body. Since the fluid doesn't exert force on the part of the body which is outside of it.

The magnitude of buoyant force may be appreciated a bit more from the following argument. Consider any object of arbitrary shape and volume V surrounded by a liquid. The force the liquid exerts on an object within the liquid is equal to the weight of the liquid with a volume equal to that of the object. This force is applied in a direction opposite to gravitational force, that is of magnitude:

where ρf is the density of the fluid, Vdisp is the volume of the displaced body of liquid, and g is the gravitational acceleration at the location in question.

If this volume of liquid is replaced by a solid body of exactly the same shape, the force the liquid exerts on it must be exactly the same as above. In other words the "buoyant force" on a submerged body is directed in the opposite direction to gravity and is equal in magnitude to

The net force on the object must be zero if it is to be a situation of fluid statics such that Archimedes principle is applicable, and is thus the sum of the buoyant force and the object's weight

If the buoyancy of an (unrestrained and unpowered) object exceeds its weight, it tends to rise. An object whose weight exceeds its buoyancy tends to sink. Calculation of the upwards force on a submerged object during its accelerating period cannot be done by the Archimedes principle alone; it is necessary to consider dynamics of an object involving buoyancy. Once it fully sinks to the floor of the fluid or rises to the surface and settles, Archimedes principle can be applied alone. For a floating object, only the submerged volume displaces water. For a sunken object, the entire volume displaces water, and there will be an additional force of reaction from the solid floor.

In order for Archimedes' principle to be used alone, the object in question must be in equilibrium (the sum of the forces on the object must be zero), therefore;

and therefore

showing that the depth to which a floating object will sink, and the volume of fluid it will displace, is independent of the gravitational field regardless of geographic location.

(Note: If the fluid in question is seawater, it will not have the same density (ρ) at every location. For this reason, a ship may display a Plimsoll line.)

It can be the case that forces other than just buoyancy and gravity come into play. This is the case if the object is restrained or if the object sinks to the solid floor. An object which tends to float requires a tension restraint force T in order to remain fully submerged. An object which tends to sink will eventually have a normal force of constraint N exerted upon it by the solid floor. The constraint force can be tension in a spring scale measuring its weight in the fluid, and is how apparent weight is defined.

If the object would otherwise float, the tension to restrain it fully submerged is:

When a sinking object settles on the solid floor, it experiences a normal force of:

It is common to define a buoyant mass mb that represents the effective mass of the object as can be measured by a gravitational method. If an object which usually sinks is submerged suspended via a cord from a balance pan, the reference object on the other dry-land pan of the balance will have mass:

where is the true (vacuum) mass of the object, and ρo and ρf are the average densities of the object and the surrounding fluid, respectively. Thus, if the two densities are equal, ρo = ρf, the object is seemingly weightless, and is said to be neutrally buoyant. If the fluid density is greater than the average density of the object, the object floats; if less, the object sinks.

Another possible formula for calculating buoyancy of an object is by finding the apparent weight of that particular object in the air (calculated in Newtons), and apparent weight of that object in the water (in Newtons). To find the force of buoyancy acting on the object when in air, using this particular information, this formula applies:

'Buoyancy force = weight of object in empty space − weight of object immersed in fluid'

The final result would be measured in Newtons.

Air's density is very small compared to most solids and liquids. For this reason, the weight of an object in air is approximately the same as its true weight in a vacuum. The buoyancy of air is neglected for most objects during a measurement in air because the error is usually insignificant (typically less than 0.1% except for objects of very low average density such as a balloon or light foam).

[edit] Stability

A floating object is stable if it tends to restore itself to an equilibrium position after a small displacement. For example, floating objects will generally have vertical stability, as if the object is pushed down slightly, this will create a greater buoyant force, which, unbalanced by the weight force, will push the object back up.

Rotational stability is of great importance to floating vessels. Given a small angular displacement, the vessel may return to its original position (stable), move away from its original position (unstable), or remain where it is (neutral).

Rotational stability depends on the relative lines of action of forces on an object. The upward buoyant force on an object acts through the center of buoyancy, being the centroid of the displaced volume of fluid. The weight force on the object acts through its center of gravity. A buoyant object will be stable if the center of gravity is beneath the center of buoyancy because any angular displacement will then produce a 'righting moment'.

[edit] Compressible fluids and objects

The atmosphere's density depends upon altitude. As an airship rises in the atmosphere, its buoyancy decreases as the density of the surrounding air decreases. In contrast, as a submarine expels water from its buoyancy tanks, it rises because its volume is constant (the volume of water it displaces if it is fully submerged) while its mass is decreased.

[edit] Compressible objects

As a floating object rises or falls, the forces external to it change and, as all objects are compressible to some extent or another, so does the object's volume. Buoyancy depends on volume and so an object's buoyancy reduces if it is compressed and increases if it expands.

If an object at equilibrium has a compressibility less than that of the surrounding fluid, the object's equilibrium is stable and it remains at rest. If, however, its compressibility is greater, its equilibrium is then unstable, and it rises and expands on the slightest upward perturbation, or falls and compresses on the slightest downward perturbation.

Submarines rise and dive by filling large tanks with seawater. To dive, the tanks are opened to allow air to exhaust out the top of the tanks, while the water flows in from the bottom. Once the weight has been balanced so the overall density of the submarine is equal to the water around it, it has neutral buoyancy and will remain at that depth.

The height of a balloon tends to be stable. As a balloon rises it tends to increase in volume with reducing atmospheric pressure, but the balloon's cargo does not expand. The average density of the balloon decreases less, therefore, than that of the surrounding air. The balloon's buoyancy decreases because the weight of the displaced air is reduced. A rising balloon tends to stop rising. Similarly, a sinking balloon tends to stop sinking.

[edit] Density

A pound coin floats in mercury due to the buoyant force upon it.

A density column containing some common liquids and solids. From top: baby oil, rubbing alcohol, vegetable oil, wax, water, and aluminum. Food coloring was added to rubbing alcohol and water for visibility.

If the weight of an object is less than the weight of the displaced fluid when fully submerged, then the object has an average density that is less than the fluid and when fully submerged will experience a force buoyancy greater than its own weight. If the fluid has a surface, such as water in a lake or the sea, the object will float and settle at a level where it displaces the same weight of fluid as the weight of the object. If the object is immersed in the fluid, such as a submerged submarine or air in a balloon, it will tend to rise. If the object has exactly the same density as the fluid, then its buoyancy equals its weight. It will remain submerged in the fluid, but it will

neither sink nor float, although a disturbance in either direction will cause it to drift away from its position. An object with a higher average density than the fluid will never experience more buoyancy than weight and it will sink. A ship will float even though it may be made of steel (which is much denser than water), because it encloses a volume of air (which is much less dense than water), and the resulting shape has an average density less than that of the water.

[edit] Beyond Archimedes' principle

Archimedes' principle is a fluid statics concept. In its simple form, it applies when the object is not accelerating relative to the fluid. To examine the case when the object is accelerated by buoyancy and gravity, the fact that the displaced fluid itself has inertia as well must be considered.[5]

This means that both the buoyant object and a parcel of fluid (equal in volume to the object) will experience the same magnitude of buoyant force because of Newton's third law, and will experience the same acceleration, but in opposite directions, since the total volume of the system is unchanged. In each case, the difference between magnitudes of the buoyant force and the force of gravity is the net force, and when divided by the relevant mass, it will yield the respective acceleration through Newton's second law. All acceleration measures are relative to the reference frame of the undisturbed background fluid.

[edit] Atwood's machine analogy

Atwood's Machine Analogy for dynamics of buoyant objects in vertical motion. The displaced parcel of fluid is indicated as the dark blue rectangle, and the buoyant solid object is indicated as the gray object. The acceleration vectors (a) in this visual depict a positively buoyant object which naturally accelerates upward, and upward acceleration of the object is our sign convention.

The system can be understood by analogy with a suitable modification of Atwood's machine, to represent the mechanical coupling of the displaced fluid and the buoyant object, as shown in the diagram right.

The solid object is represented by the gray object The fluid being displaced is represented by dark blue object Undisturbed background fluid is analogous to the inextensible massless cord The force of buoyancy is analogous to the tension in the cord The solid floor of the body of fluid is analogous to the pulley, and reverses the direction of the buoyancy force,

such that both the solid object and the displaced fluid experience their buoyancy force upward.

[edit] Results

It is important to note that this simplification of the situation completely ignores drag and viscosity, both of which come in to play to a greater extent as speed increases, when considering the dynamics of buoyant objects.

The following simple formulation makes the assumption of slow speeds such that drag and viscosity are not significant. It is difficult to carry out such an experiment in practice with speeds close to zero, but if measurements of acceleration are made as quickly as possible after release from rest, the equations below give a good approximation to the acceleration and the buoyancy force.

A system consists of a well-sealed object of mass m and volume V which is fully submerged in a uniform fluid body of density ρf and in an environment of a uniform gravitational field g. Under the forces of buoyancy and gravity alone, the "dynamic buoyant force" B acting on the object and its upward acceleration a are given by:

Buoyant force

Upward acceleration

Derivations of both of these equations originates from constructing a system of equations by means of Newton's second law for both the solid object and the displaced parcel of fluid. An equation for upward acceleration of the object is constructed by dividing the net force on the object (B − mg) by its mass m. Due to the mechanical coupling, the object's upward acceleration is equal in magnitude to the downward acceleration of the displaced fluid, an equation constructed by dividing the net force on the displaced fluid (B − ρfVg) by its mass ρfV.

Should other forces come in to play in a different situation (such as spring forces, human forces, thrust, drag, or lift), it is necessary for the solver of problem to re-consider the construction of Newton's second law and the mechanical coupling conditions for both bodies, now involving these other forces. In many situations turbulence will introduce other forces that are much more complex to calculate.

In the case of neutral buoyancy, m is equal to ρfV. Thus B reduces to mg and the acceleration is zero. If the object is much denser than the fluid, then B approaches zero and the object's upward acceleration is approximately −g, i.e. it is accelerated downward due to gravity as if the fluid were not present. As an example, a pellet of osmium falling through air will initially accelerate at 99.98% of g downward, though this will reduce as speed increases. Similarly, if the fluid is much denser than the object, then B approaches 2mg and the upward acceleration is approximately g. As an example, a typical Styrofoam ball in a tub of Mercury will initially accelerate upward at about 98.5% g.

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The metacentric height (GM) is the distance between the centre of gravity of a ship and its metacentre. The GM is used to calculate the stability of a ship and this must be done before it proceeds to sea. The GM must equal or exceed the minimum required GM for that ship for the duration of the forthcoming voyage. This is to ensure that the ship has adequate stability.

6 Measuring metacentric height 7 References 8 See also

[edit] Metacentre

When a ship is heeled, the centre of buoyancy of the ship moves laterally. The point at which a vertical line through the heeled centre of buoyancy crosses the line through the original, vertical centre of buoyancy is the metacentre. The metacentre remains directly above the centre of buoyancy regardless of the tilt of a floating body, such as a ship. In the diagram to the right the two Bs show the centres of buoyancy of a ship in the upright and heeled condition and M is the metacentre. The metacentre is considered to be fixed for small angles of heel; however, at larger angles of heel the metacentre can no longer be considered fixed and other means must be found to calculate the ship's stability.The metacentre can be calculated using the formulae:

KM = KB + BM

Where B is the centre of buoyancy, I is the Second moment of area of the waterplane in meters4 and V is the volume of displacement in meters3. KM is the distance from the keel (bottom middle section of the ship) to the metacentre. [1]

[edit] Different centres

Initially the second moment of area increases as the surface area increases, increasing BM, so Mφ moves to the opposite side, thus increasing the stability arm. When the deck is flooded, the stability arm rapidly decreases.

The centre of buoyancy, is the centre of the volume of water which the hull displaces. This point is referred to as B in naval architecture. The centre of gravity of the ship itself is known as G in naval architecture. When a ship is stable, the centre of buoyancy is vertically in-line with the centre of gravity of the ship.[2]

The metacentre is the point where the lines intersect (at angle φ) of the upward force of buoyancy of φ ± dφ. When the ship is vertical it lies above the centre of gravity and so moves in the opposite direction of heel as the ship rolls. The metacentre is known as M in naval architecture.

The distance between the centre of gravity and the metacentre is called the metacentric height, and is usually between one and two meters. This distance is also abbreviated as GM. As the ship heels over, the centre of gravity generally remains fixed with respect to the ship because it just depends upon position of the ship's weight and cargo, but the surface area increases, increasing BMφ. The metacentre, Mφ, moves up and sideways in the opposite direction in which the ship has rolled and is no longer directly over the centre of gravity.[3]

The righting force on the ship is then caused by gravity pulling down on the hull, effectively acting on its centre of gravity, and the buoyancy pushing the hull upwards; effectively acting along the vertical line passing through the centre of buoyancy and the metacentre above it. This creates a torque which rotates the hull upright again and is proportional to the horizontal distance between the centre of gravity and the metacentre. The metacentric height is important because the righting force is proportional to the metacentric height times the sine of the angle of heel.

When setting a common reference for the centres, the molded (within the plate or planking) line of the keel (K) is generally chosen; thus, the reference heights are:

KB - Centre of BuoyancyKG - Centre of GravityKM - Metacentre

[edit] Righting arm

Distance GZ is the righting arm: a notional lever through which the force of buoyancy acts.

Sailing vessels are designed to operate with a higher degree of heel than motorized vessels and the righting torque (or righting moment) at extreme angles is of high importance. This is expressed as the righting arm (known also as GZ — see diagram): the horizontal distance between the centre of buoyancy and the centre of gravity.[3]

GZ = GM sin φ [2]

Monohulled sailing vessels are designed to have a positive righting arm (the limit of positive stability) at anything up to 120º of heel, although as little as 90º (masts flat to the surface) is acceptable. As the displacement of the hull at any particular degree of list is not proportional, calculations can be difficult and the concept was not introduced formally into naval architecture until about 1970.[4]

[edit] Stability

GM and rolling period

GM has a direct relationship with a ship's rolling period. A ship with a small GM will be "tender" - have a long roll period - an excessively low or negative GM increases the risk of a ship capsizing in rough weather (see HMS Captain or the Vasa). It also puts the vessel at risk of potential for large angles of heel if the cargo or ballast shifts (see Cougar Ace). A ship with low GM is less safe if damaged and partially flooded because the lower metacentric height leaves less safety margin. For this reason, maritime regulatory agencies such as the IMO specify minimum safety margins for sea-going vessels. A larger metacentric height, on the other hand can cause a vessel to be too "stiff"; excessive stability is uncomfortable for passengers and crew. This is because the stiff vessel quickly responds to the sea as it attempts to assume the slope of the wave. An overly stiff vessel rolls with a short period and high amplitude which results in high angular acceleration. This increases the risk of damage to the ship as well as the risk cargo may break loose or shift. In contrast a "tender" ship lags behind the motion of the waves and tends to roll at lesser amplitudes. A passenger ship will typically have a long rolling period for comfort, perhaps 12 seconds while a tanker or freighter might have a rolling period of 6 to 8 seconds.

The period of roll can be estimated from the following equation[2]

Where g is the gravitational constant, k is the radius of gyration about the longitudinal axis through the centre of gravity and is the stability index.

Damaged Stability

If a ship floods, the loss of stability is due to the increase in B, the Centre of Buoyancy, and the loss of waterplane area - thus a loss of the waterplane moment of inertia - which decreases the metacentric height.[2] This additional mass will also reduce freeboard (distance from water to the deck) and the ship's angle of down flooding (minimum angle of heel at which water will be able to flow into the hull). The range of positive stability will be reduced to the angle of down flooding resulting in a reduced righting lever. When the vessel is inclined, the fluid in the flooded volume will move to the lower side, shifting its centre of gravity toward the list, further extending the heeling force. This is known as the free surface effect (see below).

Free surface effect

Further information: Free surface effect

In tanks or spaces that are partially filled with a fluid or semi-fluid (fish, ice or grain for example) as the tank is inclined the surface of the liquid, or semi-fluid, stays level. This results in a displacement of the centre of gravity of the tank or space relative to the overall centre of gravity. The effect is similar to that of carrying a large flat tray of water. When an edge is tipped, the water rushes to that side which exacerbates the tip even further.

The significance of this effect is proportional to the square of the width of the tank or compartment, so two baffles separating the area into thirds will reduce the displacement of the centre of gravity of the fluid by a factor of 9. This is always of significance in ship fuel tanks or ballast tanks, tanker cargo tanks, and in flooded or partially flooded compartments of damaged ships. Another worrying feature of free surface effect is that a positive feedback loop can be established, in which the period of the roll is equal or almost equal to the period of the motion of the centre of gravity in the fluid, resulting in each roll increasing in magnitude until the loop is broken or the ship capsizes.

This has been significant in historic capsizes, most notably the MS Herald of Free Enterprise.

Transverse and Longitudinal Metacentric heights

There is also a similar consideration in the movement of the metacentre forward and aft as a ship pitches. Metacentres are usually separately calculated for transverse (side to side) rolling motion and for lengthwise

longitudinal pitching motion. These are variously known as and , GM(t) and GM(l), or sometimes GMt and GMl .

Technically, there are different metacentric heights for any combination of pitch and roll motion, depending on the moment of inertia of the waterplane area of the ship around the axis of rotation under consideration, but they are normally only calculated and stated as specific values for the limiting pure pitch and roll motion.

Measuring metacentric height

The metacentric height is normally estimated during the design of a ship but can be determined by an inclining experiment or Inclining test once it has been built. This can also be done when a ship or offshore floating platform is in service. It can be calculated by theoretical formulas based on the shape of the structure.

The angle(s) obtained during the inclining experiment are directly related to GM (See Righting arm, above). Prior to the inclining experiment, an accounting of the 'as-built' centre of gravity is done; knowing KM and KG, the metacentric height (GM) can be calculated.

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The strength of ships is a topic of key interest to naval architects and shipbuilders. Ships which are built too strong are heavy, slow, and cost extra money to build and operate since they weigh more, whilst ships which are built too weakly suffer from minor hull damage and in some extreme cases catastrophic failure and sinking.

[edit] Loads on ship hulls

The hulls of ships are subjected to a number of loads.

Even when sitting at dockside or at anchor, the pressure of surrounding water displaced by the ship presses in on its hull.

The weight of the hull, and of cargo and components within the ship bears down on the hull. Wind blows against the hull, and waves run into it. When a ship moves, there is additional hull drag, the force of propellors, water driven up against the bow. When a ship is loaded with cargo, it may have many times its own empty weight of cargo pushing down on the

structure.

If the ship's structure, equipment, and cargo are distributed unevenly there may be large point loads into the structure, and if they are distributed differently than the distribution of buoyancy from displaced water then there are bending forces on the hull.

When ships are drydocked, and when they are being built, they are supported on regularly spaced posts on their bottoms.

[edit] Primary hull loads, strength, and bending

Diagram of ship hull (1) Sagging and (2) Hogging under loads. Bending is exaggerated for illustration purposes.

The primary strength, loads, and bending of a ship's hull are the loads that affect the whole hull, viewed from front to back and top to bottom. Though this could be considered to include overall transverse loads (from side

to side within the ship), generally it is applied to longitudinal loads (from end to end) only. The hull, viewed as a single beam, can bend

1. down in the center, known as sagging2. up in the center, known as hogging.

This can be due to:

hull, machinery, and cargo loads wave loads, with the worst cases of:

o sagging, due to a wave with length equal to the ship's length, and peaks at the bow and stern and a trough amidships

o hogging, due to a wave with length equal to the ship's length, and a peak amidships (right at the middle of the length)

Primary hull bending loads are generally highest near the middle of the ship, and usually very minor past halfway to the bow or stern.

Primary strength calculations generally consider the midships cross section of the ship. These calculations treat the whole ships structure as a single beam, using the simplified Euler-Bernoulli beam equation to calculate the strength of the beam in longitudinal bending. The moment of inertia (technically, second moment of area) of the hull section is calculated by finding the neutral or central axis of the beam and then totaling up the quantity

for each section of plate or girder making up the hull, with Iy being the moment of inertia of that section of material, b being the width (horizontal dimension) of the section, h being the height of the section (vertical dimension), A being the area of the section and d being the vertical distance of the center of that section from the neutral axis.

Primary (1), Secondary (2), and Tertiary (3) structural analysis of a ship hull. Depicted internal components include a watertight bulkhead (4) at the primary and secondary level, the ship's hull bottom structure including keel, keelsons, and transverse frames between two bulkheads (5) at the secondary level, and transverse frames (6), longitudinal stiffeners (7), and the hull plating (8) at the tertiary level.

Primary strength loads calculations usually total up the ships weight and buoyancy along the hull, dividing the hull into manageable lengthwise sections such as one compartment, arbitrary ten foot segments, or some such manageable subdivision. For each loading condition, the displaced water weight or buoyancy is calculated for that hull section based on the displaced volume of water within that hull section. The weight of the hull is similarly calculated for that length, and the weight of equipment and systems. Cargo weight is then added in to that section depending on the loading conditions being checked.

The total still water bending moment is then calculated by integrating the difference between buoyancy and total weight along the length of the ship.

For a ship in motion, additional bending moment is added to that value to account for waves it may encounter. Standard formulas for wave height and length are used, which take ship size into account. The worst possible waves are, as noted above, where either a wave crest or trough is located exactly amidships.

Those total bending loads, including still water bending moment and wave loads, are the forces that the overall hull primary beam has to be capable of withstanding.

[edit] Secondary hull loads, strength, and bending

The secondary hull loads, bending, and strength are those loads that happen to the skin structure of the ship (sides, bottom, deck) between major lengthwise subdivisions or bulkheads. For these loads, we are interested in how this shorter section behaves as an integrated beam, under the local forces of displaced water pushing back on the hull, cargo and hull and machinery weights, etc. Unlike primary loads, secondary loads are treated as applying to a complex composite panel, supported at the sides, rather than as a simple beam.

Secondary loads, strength, and bending are calculated similarly to primary loads: you determine the point and distributed loads due to displacement and weight, and determine local total forces on each unit area of the panel. Those loads then cause the composite panel to deform, usually bending inwards between bulkheads as most loads are compressive and directed inwards. Stress in the structure is calculated from the loads and bending.

[edit] Tertiary hull loads, strength, and bending

Tertiary strength and loads are the forces, strength, and bending response of individual sections of hull plate between stiffeners , and the behaviour of individual stiffener sections. Usually the tertiary loading is simpler to calculate: for most sections, there is a simple, maximum hydrostatic load or hydrostatic plus slamming load to calculate. The plate is supported against those loads at its edges by stiffeners and beams. The deflection of the plate (or stiffener), and additional stresses, are simply calculated from those loads and the theory of plates and shells.

[edit] Ship hull structure elements

Structural Elements of a Ship's Hull

This diagram shows the key structural elements of a ship's main hull (excluding the bow, stern, and deckhouse).

1. Deck plating (a.k.a. Main Deck, Weatherdeck or Strength Deck)2. Transverse bulkhead3. Inner bottom shell plating4. Hull bottom shell plating5. Transverse frame (1 of 2)6. Keel frame7. Keelson (longitudinal girder) (1 of 4)8. Longitudinal stiffener (1 of 18)9. Hull side beam

The depicted hull is a sample small double bottom (but not double hull) oil tanker.

[edit] Total loads, bending, and strength

The total load on a particular section of a ship's hull is the sum total of all primary, secondary, and tertiary loads imposed on it from all factors. The typical test case for quick calculations is the middle of a hull bottom plate section between stiffeners, close to or at the midsection of the ship, somewhere midways between the keel and the side of the ship.

[edit] Standard rules

Ship classification societies such as Det Norske Veritas, American Bureau of Shipping, and Lloyd's Register have established standard calculation forms for hull loads, strength requirements, the thickness of hull plating and reinforcing stiffeners, girders, and other structures. These methods often give a quick and dirty way to estimate strength requirements for any given ship. Almost always those methods will give conservative, or

stronger than precisely required, strength values. However, they provide a detailed starting point for analyzing a given ship's structure and whether it meets industry common standards or not.

[edit] Material response

Modern ships are, almost without exception, built of steel. Generally this is fairly standard steel with yield strength of around 32,000 to 36,000 psi (220 to 250 MPa), and tensile strength or ultimate tensile strength (UTS) over 50,000 psi (340 MPa).

Shipbuilders today use steels which have good corrosion resistance when exposed to seawater, and which do not get brittle at low temperatures (below freezing) since many ships are at sea during cold storms in wintertime, and some older ship steels which were not tough enough at low temperature caused ships to crack in half and sink during World War II in the Atlantic.

The benchmark steel grade is ABS A, specified by the American Bureau of Shipping. This steel has a yield strength of at least 34,000 psi (230 MPa), ultimate tensile strength of 58,000 to 71,000 psi (400 to 490 MPa), must elongate at least 19% in an 8-inch (200 mm) long specimen before fracturing and 22% in a 2-inch (50 mm) long specimen.

A safety factor above the yield strength has to be applied, since steel regularly pushed to its yield strength will suffer from metal fatigue. Steels typically have a fatigue limit, below which any quantity of stress load cycles will not cause metal fatigue and cracks/failures. Ship design criteria generally assume that all normal loads on the ship, times a moderate safety factor, should be below the fatigue limit for the steel used in their construction. It is wise to assume that the ship will regularly operate fully loaded, in heavy weather and strong waves, and that it will encounter its maximum normal design operating conditions many times over its lifetime.

Designing underneath the fatigue limit coincidentally and beneficially gives large (factor of up to 6 or more) total safety factors from normal maximum operating loads to ultimate tensile failure of the structure. But those large ultimate safety margins are not the intent: the intent is that the basic operational stress and strain on the ship, throughout its intended service life, should not cause serious fatigue cracks in the structure. Very few ships ever see ultimate load conditions anywhere near their gross failure limits. It is likely that, without fatigue concerns, ship strength requirements would be somewhat lower.

See Strength of materials.

[edit] Numerical modeling

While it is possible to develop fairly accurate analyses of ship loads and responses by hand, or using minimal computer help such as spreadsheets, modern CAD computer programs are usually used today to generate much more detailed and powerful computer models of the structure. Finite element analysis tools are used to measure the behaviour in detail as loads are applied. These programs can handle much more complex bending and point load calculations than human engineers are able to do in reasonable amounts of time.

However, it is still important to be able to manually calculate rough behaviour of ship hulls. Engineers do not trust the output of computer programs without some general reality checking that the results are within the expected order of magnitude. And preliminary designs may be started before enough information on a structure is available to perform a computer analysis.

Propeller pitch determines the speed and power that a propeller will produce. The amount of propeller pitch refers to the angle of the propeller blades as compared to the propeller hub or a horizontal line drawn through the center of the propeller. By altering the propeller pitch or the angle of the blades, the propeller can be tuned to deliver more top speed or more slow speed power or torque. This is only part of the equation, however; propeller pitch is used hand in hand with propeller blade cupping as well as material used in its production to produce the proper propeller for any given application.

Performance propellers are typically made of stainless steel, while the typical pleasure boat is equipped with an aluminum or composite propeller. Due in part to cost, the aluminum propeller blades are used because they can be easily replaced in the event of damage from striking an underwater object. Many times the aluminum propellers will bend instead of breaking. This allows an experienced repair person to reset the propeller pitch and straighten the bent propeller. In the case of a composite propeller, more often than not, the propeller blades will break off when encountering an obstacle.

Stainless steel propellers are much thinner than composite or aluminum types. This thin design coupled with the proper propeller pitch makes for a very high-performance propeller. Producing more speed at top end as well as being able to push the boat on plane much faster, the typical stainless steel propeller is engineered with the propeller pitch and cupping to extract the top level of performance from the outboard motor. This performance does not come cheap, and most stainless steel propellers are purchased at double the price of a comparable aluminum unit.

The amount of cupping designed into a propeller has as much to do with its level of effectiveness or performance as the propeller pitch does. The cupping affects the manner in which the water spins off of the propeller blade. Much in the same manner as a baseball is controlled by the placement of the pitcher's fingers as it is thrown, the cupping controls the manner in which the water is actually driven off of the propeller blades. By increasing the speed at which water is propelled off of the propeller blades, the speed at which water can enter the area occupied by the propeller is also increased. A properly tuned propeller is actually pulling water from underneath the entire length of the boat's hull.

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A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and air or water is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's principle and Newton's third law. A propeller is often colloquially known as screw both in aviation and maritime.

[edit] History

Ship propeller from 1843. Designed by C F Wahlgren based on one of John Ericsson propellers. It was fitted to the steam ship s/s Flygfisken built at the Motala dockyard.

The principle employed in using a screw propeller is used in sculling. It is part of the skill of propelling a Venetian gondola but was used in a less refined way in other parts of Europe and probably elsewhere. For example, propelling a canoe with a single paddle using a "j-stroke" involves a related but not identical technique. In China, sculling, called "lu", was also used by the 3rd century AD.

In sculling, a single blade is moved through an arc, from side to side taking care to keep presenting the blade to the water at the effective angle. The innovation introduced with the screw propeller was the extension of that arc through more than 360° by attaching the blade to a rotating shaft. Propellers can have a single blade, but in practice there are nearly always more than one so as to balance the forces involved.

The origin of the actual screw propeller starts with Archimedes, who used a screw to lift water for irrigation and bailing boats, so famously that it became known as Archimedes' screw. It was probably an application of spiral movement in space (spirals were a special study of Archimedes) to a hollow segmented water-wheel used for irrigation by Egyptians for centuries. Leonardo da Vinci adopted the principle to drive his theoretical helicopter, sketches of which involved a large canvas screw overhead.

In 1784, J. P. Paucton proposed a gyrocopter-like aircraft using similar screws for both lift and propulsion. At about the same time, James Watt proposed using screws to propel boats, although he did not use them for his steam engines. This was not his own invention, though; Toogood and Hays had patented it a century earlier, and it had become a common use as a means of propelling boats since that time.

By 1827, Czech constructor Josef Ressel had invented a screw propeller which had multiple blades fastened around a conical base; this new method of propulsion allowed steam ships to travel at much greater speeds without using sails thereby making ocean travel faster (first tests with the Austro-Hungarian Navy[citation needed]).

John Patch, a mariner in Yarmouth, Nova Scotia developed a two-bladed, fan-shaped propeller in 1832 and publicly demonstrated it in 1833, propelling a row boat across Yarmouth Harbour and a small coastal schooner at Saint John, New Brunswick, but his patent application in the United States was rejected until 1849 because he was not American citizen[1] His efficient design drew praise in American scientific circles[2] but by this time there were multiple competing versions of the marine propeller.

In 1835, when Francis Pettit Smith discovered a new way of building propellers. Up to that time, propellers were literally screws, of considerable length. But during the testing of a boat propelled by one, the screw snapped off, leaving a fragment shaped much like a modern boat propeller. The boat moved faster with the broken propeller.[3] At about the same time, Frédéric Sauvage and John Ericsson applied for patents on vaguely similar, although less efficient shortened-screw propellers, leading to an apparently permanent controversy as to who the official inventor is among those three men. Ericsson became widely famous when he built the Monitor, an armoured battleship that in 1862 fought the Confederate States’ Virginia in an American Civil War sea battle.

The first screw propeller to be powered by a gasoline engine, fitted to a small boat (now known as a powerboat) was installed by Frederick Lanchester, also from Birmingham. This was tested in Oxford. The first 'real-world' use of a propeller was by David Bushnell, who used hand-powered screw propellers to navigate his submarine "Turtle" in 1776.

The superiority of screw against paddles was taken up by navies. Trials with Smith's SS Archimedes , the first steam driven screw, led to the famous tug-of-war competition in 1845 between the screw-driven HMS Rattler and the paddle steamer HMS Alecto ; the former pulling the latter backward.

In the second half of the nineteenth century, several theories were developed. The momentum theory or Disk actuator theory—a theory describing a mathematical model of an ideal propeller—was developed by W.J.M. Rankine (1865), Alfred George Greenhill (1888) and R.E. Froude (1889). The propeller is modeled as an infinitely thin disc, inducing a constant velocity along the axis of rotation. This disc creates a flow around the propeller. Under certain mathematical premises of the fluid, there can be extracted a mathematical connection between power, radius of the propeller, torque and induced velocity. Friction is not included.

The blade element theory (BET) is a mathematical process originally designed by William Froude (1878), David W. Taylor (1893) and Stefan Drzewiecki to determine the behavior of propellers. It involves breaking an airfoil down into several small parts then determining the forces on them. These forces are then converted into accelerations, which can be integrated into velocities and positions.

A World War I wooden aircraft propeller on a workbench.

Postage stamp, USA, 1923.

The twisted airfoil (aerofoil) shape of modern aircraft propellers was pioneered by the Wright brothers. While both the blade element theory and the momentum theory had their supporters, the Wright brothers were able to combine both theories. They found that a propeller is essentially the same as a wing and so were able to use data collated from their earlier wind tunnel experiments on wings. They also found that the relative angle of attack from the forward movement of the aircraft was different for all points along the length of the blade, thus it was

necessary to introduce a twist along its length. Their original propeller blades are only about 5% less efficient than the modern equivalent, some 100 years later.[4]

Alberto Santos Dumont was another early pioneer, having designed propellers before the Wright Brothers (albeit not as efficient) for his airships. He applied the knowledge he gained from experiences with airships to make a propeller with a steel shaft and aluminium blades for his 14 bis biplane. Some of his designs used a bent aluminium sheet for blades, thus creating an airfoil shape. These are heavily undercambered because of this and combined with the lack of a lengthwise twist made them less efficient than the Wright propellers. Even so, this was perhaps the first use of aluminium in the construction of an airscrew.

[edit] Aviation

Main article: Propeller (aircraft)

Aircraft propellers convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal. The most modern propeller designs use high-technology composite materials.

[edit] Marine

Marine propeller nomenclature

1) Trailing edge2) Face3) Fillet area4) Hub or Boss5) Hub or Boss Cap

6) Leading edge7) Back8) Propeller shaft9) Stern tube bearing10) Stern tube

A propeller is the most common propulsor on ships, imparting momentum to a fluid which causes a force to act on the ship.

The ideal efficiency of any size propeller (free-tip) is that of an actuator disc in an ideal fluid. An actual marine propeller is made up of sections of helicoidal surfaces which act together 'screwing' through the water (hence the common reference to marine propellers as "screws"). Three, four, or five blades are most common in marine propellers, although designs which are intended to operate at reduced noise will have more blades. The blades are attached to a boss (hub), which should be as small as the needs of strength allow - with fixed pitch propellers the blades and boss are usually a single casting.

An alternative design is the controllable pitch propeller (CPP, or CRP for controllable-reversible pitch), where the blades are rotated normal to the drive shaft by additional machinery - usually hydraulics - at the hub and control linkages running down the shaft. This allows the drive machinery to operate at a constant speed while the propeller loading is changed to match operating conditions. It also eliminates the need for a reversing gear and allows for more rapid change to thrust, as the revolutions are constant. This type of propeller is most

common on ships such as tugs[citation needed] where there can be enormous differences in propeller loading when towing compared to running free, a change which could cause conventional propellers to lock up as insufficient torque is generated. The downsides of a CPP/CRP include: the large hub which decreases the torque required to cause cavitation, the mechanical complexity which limits transmission power and the extra blade shaping requirements forced upon the propeller designer.

For smaller motors there are self-pitching propellers. The blades freely move through an entire circle on an axis at right angles to the shaft. This allows hydrodynamic and centrifugal forces to 'set' the angle the blades reach and so the pitch of the propeller.

A propeller that turns clockwise to produce forward thrust, when viewed from aft, is called right-handed. One that turns anticlockwise is said to be left-handed. Larger vessels often have twin screws to reduce heeling torque, counter-rotating propellers, the starboard screw is usually right-handed and the port left-handed, this is called outward turning. The opposite case is called inward turning. Another possibility is contra-rotating propellers, where two propellers rotate in opposing directions on a single shaft, or on separate shafts on nearly the same axis. One example of the latter is the CRP Azipod by the ABB Group. Contra-rotating propellers offer increased efficiency by capturing the energy lost in the tangential velocities imparted to the fluid by the forward propeller (known as "propeller swirl"). The flow field behind the aft propeller of a contra-rotating set has very little "swirl", and this reduction in energy loss is seen as an increased efficiency of the aft propeller.

[edit] Additional designs

An azimuthing propeller is a vertical axis propeller.

The blade outline is defined either by a projection on a plane normal to the propeller shaft (projected outline) or by setting the circumferential chord across the blade at a given radius against radius (developed outline). The outline is usually symmetrical about a given radial line termed the median. If the median is curved back relative to the direction of rotation the propeller is said to have skew back. The skew is expressed in terms of circumferential displacement at the blade tips. If the blade face in profile is not normal to the axis it is termed raked, expressed as a percentage of total diameter.

Each blade's pitch and thickness varies with radius, early blades had a flat face and an arced back (sometimes called a circular back as the arc was part of a circle), modern propeller blades have aerofoil sections. The camber line is the line through the mid-thickness of a single blade. The camber is the maximum difference between the camber line and the chord joining the trailing and leading edges. The camber is expressed as a percentage of the chord.

The radius of maximum thickness is usually forward of the mid-chord point with the blades thinning to a minimum at the tips. The thickness is set by the demands of strength and the ratio of thickness to total diameter is called blade thickness fraction.

The ratio of pitch to diameter is called pitch ratio. Due to the complexities of modern propellers a nominal pitch is given, usually a radius of 70% of the total is used.

Blade area is given as a ratio of the total area of the propeller disc, either as developed blade area ratio or projected blade area ratio.

This section requires expansion.

Most propellers have their axis of rotation parallel to the fluid flow. There have however been some attempts to power vehicles with the same principles behind vertical axis wind turbines, where the rotation is perpendicular

to fluid flow. Most attempts have been unsuccessful. Blades that can vary their angle of attack during rotation have aerodynamics similar to flapping flight. Flapping flight is still poorly understood and almost never seriously used in engineering because of the strong coupling of lift, thrust and control forces.

The fanwing is one of the few types that has actually flown. It takes advantage of the trailing edge of an airfoil to help encourage the circulation necessary for lift.

The Voith-Schneider propeller pictured below is another successful example, operating in water.

[edit] History of ship and submarine screw propellers

A propeller from the Lusitania

James Watt of Scotland is generally credited with applying the first screw propeller to an engine, an early steam engine, beginning the use of an hydrodynamic screw for propulsion.

Mechanical ship propulsion began with the steam ship. The first successful ship of this type is a matter of debate; candidate inventors of the 18th century include William Symington, the Marquis de Jouffroy, John Fitch and Robert Fulton, however William Symington's ship the Charlotte Dundas is regarded as the world's "first practical steamboat". Paddlewheels as the main motive source became standard on these early vessels (see Paddle steamer). Robert Fulton had tested, and rejected, the screw propeller.

Sketch of hand-cranked vertical and horizontal screws used in Bushnell's Turtle, 1775

The screw (as opposed to paddlewheels) was introduced in the latter half of the 18th century. David Bushnell's invention of the submarine (Turtle) in 1775 used hand-powered screws for vertical and horizontal propulsion. The Bohemian engineer Josef Ressel designed and patented the first practicable screw propeller in 1827. Francis Pettit Smith tested a similar one in 1836. In 1839, John Ericsson introduced practical screw propulsion into the United States. Mixed paddle and propeller designs were still being used at this time (vide the 1858 SS Great Eastern).

In 1848 the British Admiralty held a tug of war contest between a propeller driven ship, Rattler, and a paddle wheel ship, Alecto. Rattler won, towing Alecto astern at 2.5 knots (4.6 km/h), but it was not until the early 20th

century that paddle propelled vessels were entirely superseded. The screw propeller replaced the paddles owing to its greater efficiency, compactness, less complex power transmission system, and reduced susceptibility to damage (especially in battle)

Voith-Schneider propeller

Initial designs owed much to the ordinary screw from which their name derived - early propellers consisted of only two blades and matched in profile the length of a single screw rotation. This design was common, but inventors endlessly experimented with different profiles and greater numbers of blades. The propeller screw design stabilized by the 1880s.

In the early days of steam power for ships, when both paddle wheels and screws were in use, ships were often characterized by their type of propellers, leading to terms like screw steamer or screw sloop.

Propellers are referred to as "lift" devices, while paddles are "drag" devices.

Cavitation damage evident on the propeller of a personal watercraft.

[edit] Marine propeller cavitation

Cavitation can occur if an attempt is made to transmit too much power through the screw, or if the propeller is operating at a very high speed. Cavitation can occur in many ways on a propeller. The two most common types of propeller cavitation are suction side surface cavitation and tip vortex cavitation.

Suction side surface cavitation forms when the propeller is operating at high rotational speeds or under heavy load (high blade lift coefficient). The pressure on the upstream surface of the blade (the "suction side") can drop below the vapour pressure of the water, resulting in the formation of a pocket of vapour. Under such conditions, the change in pressure between the downstream surface of the blade (the "pressure side") and the suction side is limited, and eventually reduced as the extent of cavitation is increased. When most of the blade surface is covered by cavitation, the pressure difference between the pressure side and suction side of the blade drops considerably, and thrust produced by the propeller drops. This condition is called "thrust breakdown". This effect wastes energy, makes the propeller "noisy" as the vapour bubbles collapse, and most seriously, erodes the screw's surface due to localized shock waves against the blade surface.

Tip vortex cavitation is caused by the extremely low pressures formed at the core of the tip vortex. The tip vortex is caused by fluid wrapping around the tip of the propeller; from the pressure side to the suction side.

This video demonstrates tip vortex cavitation well. Tip vortex cavitation typically occurs before suction side surface cavitation and is less damaging to the blade, since this type of cavitation doesn't collapse on the blade, but some distance downstream.

Cavitation can be used as an advantage in design of very high performance propellers, in form of the supercavitating propeller. In this case, the blade section is designed such that the pressure side stays wetted while the suction side is completely covered by cavitation vapor. Because the suction side is covered with vapor instead of water it encounters very low viscous friction, making the supercavitating (SC) propeller comparably efficient at high speed. The shaping of SC blade sections however, make it inefficient at low speeds, when the suction side of the blade is wetted. (See also fluid dynamics).

A similar, but quite separate issue, is ventilation, which occurs when a propeller operating near the surface draws air into the blades, causing a similar loss of power and shaft vibration, but without the related potential blade surface damage caused by cavitation. Both effects can be mitigated by increasing the submerged depth of the propeller: cavitation is reduced because the hydrostatic pressure increases the margin to the vapor pressure, and ventilation because it is further from surface waves and other air pockets that might be drawn into the slipstream.

14-ton propeller from Voroshilov a Kirov class cruiser on display in Sevastopol

[edit] Forces acting on an aerofoil

The force (F) experienced by an aerofoil blade is determined by its area (A), chord (c), velocity (V) and the angle of the aerofoil to the flow, called angle of attack (α), where:

The force has two parts - that normal to the direction of flow is lift (L) and that in the direction of flow is drag (D). Both are expressed non-dimensionally as:

and

Each coefficient is a function of the angle of attack and Reynolds' number. As the angle of attack increases lift rises rapidly from the no lift angle before slowing its increase and then decreasing, with a sharp drop as the stall angle is reached and flow is disrupted. Drag rises slowly at first and as the rate of increase in lift falls and the angle of attack increases drag increases more sharply.

For a given strength of circulation (τ), Lift = L = ρVτ. The effect of the flow over and the circulation around the aerofoil is to reduce the velocity over the face and increase it over the back of the blade. If the reduction in

pressure is too much in relation to the ambient pressure of the fluid, cavitation occurs, bubbles form in the low pressure area and are moved towards the blade's trailing edge where they collapse as the pressure increases, this reduces propeller efficiency and increases noise. The forces generated by the bubble collapse can cause permanent damage to the surfaces of the blade.

[edit] Propeller thrust

[edit] Single blade

Taking an arbitrary radial section of a blade at r, if revolutions are N then the rotational velocity is . If the blade was a complete screw it would advance through a solid at the rate of NP, where P is the pitch of the blade. In water the advance speed is rather lower, , the difference, or slip ratio, is:

where is the advance coefficient, and is the pitch ratio.

The forces of lift and drag on the blade, dA, where force normal to the surface is dL:

where:

These forces contribute to thrust, T, on the blade:

where:

As ,

From this total thrust can be obtained by integrating this expression along the blade. The transverse force is found in a similar manner:

Substituting for and multiplying by r, gives torque as:

which can be integrated as before.

The total thrust power of the propeller is proportional to and the shaft power to . So efficiency is . The blade efficiency is in the ratio between thrust and torque:

showing that the blade efficiency is determined by its momentum and its qualities in the form of angles and , where is the ratio of the drag and lift coefficients.

This analysis is simplified and ignores a number of significant factors including interference between the blades and the influence of tip vortices.

[edit] Thrust and torque

The thrust, T, and torque, Q, depend on the propeller's diameter, D, revolutions, N, and rate of advance, Va, together with the character of the fluid in which the propeller is operating and gravity. These factors create the following non-dimensional relationship:

where f1 is a function of the advance coefficient, f2 is a function of the Reynolds' number, and f3 is a function of the Froude number. Both f2 and f3 are likely to be small in comparison to f1 under normal operating conditions, so the expression can be reduced to:

For two identical propellers the expression for both will be the same. So with the propellers T1,T2, and using the same subscripts to indicate each propeller:

For both Froude number and advance coefficient:

where λ is the ratio of the linear dimensions.

Thrust and velocity, at the same Froude number, give thrust power:

For torque:

...

[edit] Actual performance

When a propeller is added to a ship its performance is altered; there is the mechanical losses in the transmission of power; a general increase in total resistance; and the hull also impedes and renders non-uniform the flow through the propeller. The ratio between a propeller's efficiency attached to a ship ( ) and in open water ( ) is termed relative rotative efficiency.

The overall propulsive efficiency (an extension of effective power ( )) is developed from the propulsive coefficient ( ), which is derived from the installed shaft power ( ) modified by the effective power for the hull with appendages ( ), the propeller's thrust power ( ), and the relative rotative efficiency.

P'E/PT = hull efficiency = ηH

PT/P'D = propeller efficiency = ηO

P'D/PD = relative rotative efficiency = ηR

PD/PS = shaft transmission efficiency

Producing the following:

The terms contained within the brackets are commonly grouped as the quasi-propulsive coefficient ( , ). The is produced from small-scale experiments and is modified with a load factor for full size ships.

Wake is the interaction between the ship and the water with its own velocity relative to the ship. The wake has three parts: the velocity of the water around the hull; the boundary layer between the water dragged by the hull and the surrounding flow; and the waves created by the movement of the ship. The first two parts will reduce the velocity of water into the propeller, the third will either increase or decrease the velocity depending on whether the waves create a crest or trough at the propeller.

[edit] Types of marine propellers

[edit] Controllable pitch propeller

A controllable pitch propeller

At present, one of the newest and best type of propeller is the controllable pitch propeller. This propeller has several advantages with ships. These advantages include: the least drag depending on the speed used, the ability to move the sea vessel backwards, and the ability to use the "vane"-stance, which gives the least water resistance when not using the propeller (e.g. when the sails are used instead).

[edit] Skewback propeller

An advanced type of propeller used on German Type 212 submarines is called a skewback propeller. As in the scimitar blades used on some aircraft, the blade tips of a skewback propeller are swept back against the direction of rotation. In addition, the blades are tilted rearward along the longitudinal axis, giving the propeller an overall cup-shaped appearance. This design preserves thrust efficiency while reducing cavitation, and thus makes for a quiet, stealthy design.[5]

See also: astern propulsion

[edit] Modular propeller

A modular propeller provides more control over the boats performance. There is no need to change an entire prop, when there is an opportunity to only change the pitch or the damaged blades. Being able to adjust pitch will allow for boaters to have better performance while in different altitudes, water sports, and/or cruising.[6]

[edit] Protection of small engines

A failed rubber bushing in an outboard's propeller

For smaller engines, such as outboards, where the propeller is exposed to the risk of collision with heavy objects, the propeller often includes a device which is designed to fail when over loaded; the device or the whole propeller is sacrificed so that the more expensive transmission and engine are not damaged.

Typically in smaller (less than 10 hp/7.5 kW) and older engines, a narrow shear pin through the drive shaft and propeller hub transmits the power of the engine at normal loads. The pin is designed to shear when the propeller is put under a load that could damage the engine. After the pin is sheared the engine is unable to provide propulsive power to the boat until an undamaged shear pin is fitted.[7] Note that some shear pins used to have shear grooves machined into them. Nowadays the grooves tend to be omitted. The result of this oversight is that the torque required to shear the pin rises as the cutting edges of the propeller bushing and shaft become blunted. Eventually the gears will strip instead.

In larger and more modern engines, a rubber bushing transmits the torque of the drive shaft to the propeller's hub. Under a damaging load the friction of the bushing in the hub is overcome and the rotating propeller slips on the shaft preventing overloading of the engine's components.[8] After such an event the rubber bushing itself may be damaged. If so, it may continue to transmit reduced power at low revolutions but may provide no power, due to reduced friction, at high revolutions. Also the rubber bushing may perish over time leading to its failure under loads below its designed failure load.

Whether a rubber bushing can be replaced or repaired depends upon the propeller; some cannot. Some can but need special equipment to insert the oversized bushing for an interference fit. Others can be replaced easily.

The "special equipment" usually consists of a tapered funnel, some kind of press and rubber lubricant (soap). Often the bushing can be drawn into place with nothing more complex than a couple of nuts, washers and "allscrew" (threaded bar). If one does not have access to a lathe an improvised funnel can be made from steel tube and car body filler! (as the filler is only subject to compressive forces it is able to do a good job) A more serious problem with this type of propeller is a "frozen-on" spline bushing which makes propeller removal impossible. In such cases the propeller has to be heated in order to deliberately destroy the rubber insert. Once the propeller proper is removed, the splined tube can be cut away with a grinder. A new spline bushing is of course required. To prevent the problem recurring the splines can be coated with anti-seize anti-corrosion compound.

In some modern propellers, a hard polymer insert called a drive sleeve replaces the rubber bushing. The splined or other non-circular cross section of the sleeve inserted between the shaft and propeller hub transmits the engine torque to the propeller, rather than friction. The polymer is weaker than the components of the propeller and engine so it fails before they do when the propeller is overloaded.[9] This fails completely under excessive load but can easily be replaced.

REPUBLICA BOLIVARIANA DE VENEZUELAMINISTERIO DEL PODER POPULAR PARA LA DEFENSA

UNIVERSIDAD EXPERIMENTAL DE LAS FUERZAS ARMADASUNEFA PUERTO CABELLO EDO CARABOBO

HANDOUT Nº 8

The term "waterline" generally refers to the line where the hull of a ship meets the water surface. It is also the name of a special marking, also known as the national Load Line or Plimsoll Line, to be positioned amidships, that indicates the draft of the ship and the legal limit to which a ship may be loaded for specific water types and temperatures. Temperature affects the level because warm water provides less buoyancy, being less dense than cold water. The salinity of the water also affects the level, fresh water being less dense than salty seawater. This marking was invented in the 1870s by Samuel Plimsoll.

For vessels with displacement hulls, the hull speed is determined by, amongst other things, the waterline length. In a sailing boat, the waterline length can change significantly as the boat heels, and can dynamically affect the speed of the boat.

In aircraft design, the term "waterline" refers to the vertical location of items on the aircraft. This is the (normally) "Z" axis of an XYZ coordinate system, the other two axes being the Fuselage Station (X) and Buttock Line (Y).

The purpose of a 'load line' is to ensure that a ship has sufficient freeboard (the height from the water line to the main deck) and thus sufficient reserve buoyancy (e.g., the enclosed volume created by the area between the waterline and the main deck). The freeboard of commercial vessels is measured between the lowest point of the uppermost continuous deck at side and the waterline and this must not be less than the freeboard marked on the Load Line Certificate issued to that ship. All commercial ships, other than in exceptional circumstances,[1] have a load line symbol painted amidships on each side of the ship. This symbol must also be permanently marked, so that if the paint wears off it remains visible. The load line makes it easy for anyone to determine if a ship has been overloaded. The exact location of the Load Line is calculated and/or verified by a Classification Society and that society issues the relevant certificates.

This symbol, also called an international load line or Plimsoll line, indicates the maximum safe draft, and therefore the minimum freeboard for the vessel in various operating conditions.[2]

[edit] History

The first official loading regulations are thought to date back to maritime legislation originating with the kingdom of Crete in 2,500 BC when vessels were required to pass loading and maintenance inspections. Roman sea regulations also contained similar regulations.

In the Middle Ages the Venetian Republic, the city of Genoa and the Hanseatic league required ships to load to a load line. In the case of Venice this was a cross marked on the side of the ship and of Genoa three horizontal lines.

The first 19th century loading recommendations were introduced by Lloyd's Register of British and Foreign Shipping in 1835, following discussions between shipowners, shippers and underwriters. Lloyds recommended freeboards as a function of the depth of the hold (three inches per foot of depth). These recommendations, used extensively until 1880, became known as "Lloyd's Rule".

In the 1860s, after increased loss of ships due to overloading, a British MP, Samuel Plimsoll, took up the load line cause. [3] A Royal Commission on unseaworthy ships was established in 1872, and in 1876 the United Kingdom Merchant Shipping Act made the load line mark compulsory, although the positioning of the mark was not fixed by law until 1894. In 1906, laws were passed requiring foreign ships visiting British ports to be marked with a load line. It was not until 1930 (The 1930 Load Line Convention) that there was international agreement for universal application of load line regulations.

In 1966 a Load Lines Convention was held in London which re-examined and amended the 1930 rules. The 1966 Convention has since seen amendments in 1971, 1975, 1979, 1983, 1995 and 2003.[4]

[edit] Standard load line marks

Load Line Mark and Lines and Timber Load Line Mark and Lines for power driven merchant vessels

Load Line Mark and Lines for commercial sailing vessels

The original "Plimsoll Mark" was a circle with a horizontal line through it to show the maximum draft of a ship. Additional marks have been added over the years, allowing for different water densities and expected sea conditions.

Letters may also appear to the sides of the mark indicating the classification society that has surveyed the vessel's load line. The initials used include AB for the American Bureau of Shipping, LR for Lloyd's Register, GL for Germanischer Lloyd, BV for Bureau Veritas, IR for the Indian Register of Shipping, RI for the Registro Italiano Navale and NV for Det Norske Veritas. These letters should be approximately 115 millimetres in height and 75 millimetres in width.[5] The Load Line Length is referred to during and following load line calculations.

The letters on the Load line marks have the following meanings:

TF – Tropical Fresh Water F – Fresh Water T – Tropical Seawater S – Summer Temperate Seawater W – Winter Temperate Seawater

WNA – Winter North Atlantic

Fresh water is considered to have a density of 1000 kg/m³ and sea water 1025 kg/m³. Fresh water marks make allowance for the fact that the ship will float deeper in fresh water than salt water. A ship loaded to her Fresh Water mark in fresh water will float at her Summer Mark once she has passed into sea water. Similarly if loaded to her Tropical Fresh water mark she will float at her Tropical Mark once she passes in to sea water.

The Summer load line is the primary load line and it is from this mark that all other marks are derived. The position of the summer load line is calculated from the Load Line Rules and depends on many factors such as length of ship, type of ship, type and number of superstructures, amount of sheer, bow height and so on. The horizontal line through the circle of the Plimsoll mark is at the same level as the summer load line.

The Winter load line is one forty-eighth of the summer load draft below the summer load line.

The Tropical load line is one forty-eighth of the summer load draft above the summer load line.

The Fresh Water load line is an amount equal to centimetres above the summer load line where is the displacement in metric tonnes at the summer load draft and T is the metric tonnes per centimetre immersion at that draft.In any case where cannot be ascertained the fresh water load line is at the same level as the tropical load line.The position of the Tropical Fresh load line relative to the tropical load line is found in the same way as the fresh water load line is to the summer load line.The Winter North Atlantic load line is used by vessels not exceeding 100 metres in length when in certain areas of the North Atlantic Ocean during the winter period. When assigned it is 50 millimetres below the winter mark.[6]

[edit] Timber load line marks

Certain vessels are assigned Timber Freeboards but before these can be assigned certain additional conditions have to be met. One of these conditions is that the vessel must have a forecastle of at least 0.07 the length of the vessel and of not less than standard height, which is 1.8 metres for a vessel 75 metres or less in length and 2.3 metres for a vessel 125 metres or more in length with intermediate heights for intermediate lengths. A poop or raised quarter deck is also required if the length is less than 100 metres. The letter L prefixes the load line marks to indicate a timber load line.[7] Except for the Timber Winter North Atlantic freeboard the other freeboards are less than the standard freeboards. This allows these ships to carry additional timber as deck cargo, but with the facility to jettison this cargo.

The letters on the Timber Load line marks have the following meanings:

LTF – Timber Tropical Fresh Water LF – Timber Fresh Water LT – Timber Tropical Seawater LS – Timber Summer Seawater LW – Timber Winter Seawater LWNA –Timber Winter North Atlantic

The Summer Timber load line is arrived at from the appropriate tables in the Load Line Rules. [8]

The Winter Timber load line is one thirty-sixth of the Summer Timber load draft below the Summer Timber load line.

The Tropical Timber load line is one forty-eighth of the Summer Timber load draft above the Summer timber load line.

The Timber Fresh and the Tropical Timber Fresh load lines are calculated in a similar way to the Fresh Water and Tropical Fresh water load lines except that the displacement used in the formula is that of the vessel at her Summer Timber load draft. If this cannot be ascertained then these marks will be one forty-eighth of the Timber Summer draft above the Timber Summer and Timber Tropical marks respectively.[9]

The Timber Winter North Atlantic load line is at the same level as the Winter North Atlantic load line

[edit] Subdivision load line marks

Passenger ships having spaces which are adapted for the accommodation of passengers and the carriage of cargo alternatively may have one or more additional load line marks corresponding to the subdivision drafts approved for the alternative conditions. These marks show C1 for the principal passenger condition, and C2, C3, etc., for the alternative conditions, however in no case shall any subdivision load line mark be placed above the deepest load line in salt water.[10]

Subdivision Load Line Marks

Passenger vessel with no allowed Subdivision Load line

Passenger vessel with one allowed Subdivision Load line

Passenger vessel with two allowed Subdivision Load lines

REPUBLICA BOLIVARIANA DE VENEZUELAMINISTERIO DEL PODER POPULAR PARA LA DEFENSA

UNIVERSIDAD EXPERIMENTAL DE LAS FUERZAS ARMADASUNEFA PUERTO CABELLO EDO CARABOBO

HANDOUT Nº 9

ESSON TOPIC: 4.8 TITLE: RIGHTING SHIP (MOB-D-6-SF)

Contact periods allotted this LESSON TOPIC:

Classroom: 1.5 Test: 0.0

Trainer: 0.0 Total: 1.5

MEDIA: Classroom lecture with visual media

TERMINAL OBJECTIVES:

6.0 EVALUATE shipboard stability by analyzing weight and moment considerations (JTI 3.2.1, 6.0, 6.1, 6.2)

ENABLING OBJECTIVES:

6.50 For the MOB-D-6-SF Righting Ship drill:

a. STATE the purpose of the drill.

b. DESCRIBE the procedure for conducting the drill.

c. STATE the requirements for conducting the drill.

d. DESCRIBE how to employ the DCTT to evaluate the drill.

6.51 DESCRIBE the inclining experiment, including it�s mathematical basis, range of validity, and common causes for inaccuracies.

6.52 Given a change in a ship's weight distribution, CALCULATE the resulting list using the moment to heel one degree (MH1�) equation.

6.53 Given a ship's list, CALCULATE the necessary transverse moment to correct the list, using the moment to heel one degree (MH1�) equation.

DEFINITIONS

 

Roll: The action of a vessel involving a recurrent motion, usually caused by wave action.

Heel: Semi-permanent angle of inclination caused by external forces, such as high speed turns, beam winds, and seas.

List: Permanent angle of inclination, caused by:

 

     

  1. Ship�s Center of Gravity transversely shifted from centerline.

 

  2. Negative Metacentric Height (-GM)  

  3. Combination of Gravity off-centerline and -GM  

     

 

MOMENT TO HEEL 1o EQUATION

When a ship experiences an Inclining Moment (IM) the vessel will list or heel until the Righting Moment (RM) is equal to the Inclining Moment (RM = IM). The Inclining Moment is simply a force acting through some distance.

 

This is only true when the ship has a negligible heel or list.

 

As the vessel inclines, the distance between the forces changes.

 

A relationship can be developed to solve for the distance between forces for all angles of heel. Using an expanded drawing of the triangle from the above diagram:

 

 

 

Using the cosine equation to solve for the distance X:

 

 

Therefore:

 

     

   

     

A Righting Moment is created by the ship to keep itself upright. In this case, the force is equal to the ship's displacement (WF) and the distance is the ship's righting arm (GZ) at each particular angle of heel.

The Righting Arm (GZ) changes with inclination of the ship. Using the relationship derived in Unit 4.01 for small angles of heel:

NOTE: This relationship holds true for angles less than 7�-10�

 

Therefore:

     

   

     

 

The initial premise was that RM = IM:

 

Transferring cos to the right:

 

 

Choosing a specific angle, the moment (w x d) required to create that list or heel can be found. Using 1o:

tan 1o = 0.01746

Therefore:

     

   

     

This formula is valid for angles less than 10o due to movement of the metacenter. To check this formula for all inclinations less than 10o, a comparison between the MH10o and 10 times MH1o is made.

-vs-

 

and

 

There is a 0.0017 difference over the 10�range. This error is negligible. The list equation can now be used.

     

   

     

 

Example

Your ship has a 1.5o list to starboard. There are 50 LT of spare parts sitting on the starboard side. The CHENG wants to know how far to transfer the spare parts to correct the list.

  Step 1: Calculate MH1o:

 

Step 2: Use the list equation to solve for distance:

 

or

 

Example

Your ship has a 2.8� list to port. The CO wants it corrected. There are 3,200 gallons of fuel in the port wing tank (DFM 322 Gal/LT). The starboard wing tank is empty. Correct the list using the fuel and a set of 5 forklifts (8 LT each). The forklifts may only be moved 15 FT to starboard before hitting the bulkhead. How long will it take to correct the list?

 

 

 

WO = 4200 LT

KM = 23.5 FT

KG = 19.75 FT

 

Step 1: Calculate MH1�:

 

 

 

Step 2: Calculate the amount of list corrected by shifting fuel:

 

 

 

 

or

Step 3: So far, we have corrected 1.27o of the 2.8o list. Using the forklifts, we will correct for the remaining 1.53o list.

 

or

 

 

Step 4: Finally, calculate how long it takes to transfer 3,200 gallons of fuel when the pump capacity is 150 gallons per minute.

 

 

Assuming it takes less than 21.33 minutes to move 5 forklifts, this is the time required to correct the list.

INCLINING EXPERIMENT

The inclining experiment is completed upon commissioning and following each major overhaul. It is performed to obtain accurately the vertical height of the ship�s center of gravity above the keel (KGo). Details of the procedures and requirements are spelled out in Section 4, NSTM 079 volume 1, Damage Control Stability and Buoyancy.

 

Who will get involved:

1. Ship�s Damage Control Assistant

2. NAVSEA / Engineering Logistics Center

3. F/O and Water King

4. Yard Naval Architect

5. SUPSHIP / Cutter Type Desk

6. Pendulum Riggers

7. CHENG

8. Except for necessary watches, ship�s force is put ashore

 

Procedures:

The naval shipyard or building yard at which the inclining experiment is to be performed will issue a memorandum to the ship outlining the necessary work to be done by ship�s force and by the yard to prepare the ship for inclining.

 

1. Liquid load will be in accordance with the memorandum.

2. Inventory of all consumables to be made by ship�s force and inclining party.

3. Inclining weights are placed on centerline.

4. Freeboard is measured, and a photo of the drafts is taken.

5. Salinity of saltwater is measured.

8. Pendulums set up forward, midships, and aft.

9. Weights are moved off-centerline.

10.Inclination of the ship measured.

 

Measurements are taken for several weight movements both port and starboard. The Naval Architect then uses the following equation:

Where:

w = Inclining Weights (LT)

d = Athwartships Distance Weights Were Moved (FT)

WF = Displacement of Ship (LT, with Inclining Weights)

tan = Movement of Pendulum Length of Pendulum

 

The inclining experiment measures GM accurately, and since the ship�s drafts are known, KM can be found on the Draft Diagram and Functions of Form. KG is then found using KG = KM - GM.

 

USS/USCG_________________________ DATE _______________

PURPOSE: TO TRAIN THE DAMAGE CONTROL ORGANIZATION IN CORRECTING A LIST.

REQUIREMENTS: CONDITION ONE WITH DAMAGE CONTROL MATERIAL CONDITION ZEBRA SET. LIQUID LOADING MAY BE VARIED TO PUT AN ACTUAL LIST OR TRIM ON THE SHIP IF DESIRED.

PREREQUISITES: 1. ONE OR MORE TANKS OR COMPARTMENTS ARE SIMULATED FLOODED/OPEN TO THE SEA.

2. FLOODING BOUNDARIES HAVE BEEN SET.

3. FLOODING IS UNDER CONTROL.

4. EMERGENCY PATCHING, PLUGGING AND SHORING HAS BEEN COMPLETED.

5. CORRECTION OF THE SHIPS LIST OR TRIM AND SHORING ORDERED.

LIMITS OF THE DRILL:

1. ONLY COUNTER FLOODING OR SHIFTING OF THE LIQUID LOAD IS AUTHORIZED AS CORRECTIVE ACTION.

1. PROPER DISSEMINATION OF INFORMATION AND REPORTS. 15________

A. READINESS OF REFERENCES 5

1. FLOODING EFFECTS AND LIQUID LOAD DIAGRAM.

2. UP-TO-DATE LIQUID LOAD LIST.

3. FUEL OIL TRANSFER BILL.

A. FUEL OIL TANK SEQUENCE TABLES.

4. COUNTER FLOODING BILL.

5. FLOODING EFFECTS BILL.

B. COMPLETENESS AND CORRECTNESS OF DC MESSAGES. 5

1. COMPLETE SET OF DAMAGE CONTROL WRITTEN MESSAGES.

2. USE OF STANDARD PHONE TALKER PROCEDURES.

C. INFORMATION TO THE CAPTAIN 5

1. EXTENT OF DAMAGE.

2. CORRECTIVE MEASURES TAKEN/PLANNED.

2. ACTION OF REPAIR PARTY TO DETERMINE THE EXTENT OF FLOODING AND LIQUID LOAD AT START OF PROBLEM. 15 __________________

A. PREPARATION OF THE INVESTIGATORS 5

1. INVESTIGATION KIT COMPLETE

2. FAMILIARIZATION WITH ASSIGNED AREAS.

3. CORRECTIONS OF INVESTIGATION TECHNIQUES.

B. WAS THE REPAIR PARTY AWARE OF THE LIQUID LEVELS PRIOR TO CASUALTY?

C. WAS THE REPAIR PARTY OFFICER KNOWLEDGEABLE OF THE SHIP'S STABILITY AND SUBDIVISION CHARACTERISTICS?

3. ABILITY OF THE DAMAGE CONTROL PERSONNEL TO COMPUTE EFFECT OF DAMAGE AND TO DETERMINE MEANS OF COUNTERFLOODING OR SHIFTING THE LIQUID LOAD TO CORRECT THE LIST OR TRIM.

40 _________________

A. THE ABILITY TO DECIPHER THE FLOODING EFFECTS AND LIQUID LOAD DIAGRAM AND USE FLOODING EFFECT BILL. 10

B. KNOWLEDGE OF PUMPING OR SLUICING LIQUIDS ACROSS THE SHIP.

10

C. KNOWLEDGE OF PROCEDURES TO COUNTER FLOOD. 5

D. UNDERSTANDING THE CONSEQUENCES OF CONTAMINATION. 5

E. UNDERSTANDING THE FUEL OIL TANK SEQUENCE TABLES. 5

F. UNDERSTANDING THE EFFECTS OF DEWATERING/FLOODING SOLID/PARTIAL FLOODED COMPARTMENTS ABOVE CENTER OF GRAVITY. 5

4. ACTION OF THE REPAIR PARTY IN COUNTER FLOODING AND SHIFTING OF LIQUID LOAD. 30 ____________

A. THE ABILITY TO IDENTIFY AND LOCATE SELECTED SYSTEM CONTROL VALVES. 10

B. KNOWLEDGE OF THE INSTALLED SYSTEMS 10

1. FUEL OIL TRANSFER SYSTEM.

2. DRAINAGE SYSTEM.

3. FLOODING AND BALLASTING SYSTEMS.

4. PUMP CAPACITIES.

C. HANDLING OF SELF-INFLICTED DAMAGES 10

1. LACK OF SYSTEM MAINTENANCE (PMS)

2. FAILURE TO PROPERLY OPERATE CONTROLS.

3. INSUFFICIENT OR IMPROPER DC CLASSIFICATIONS.

REPUBLICA BOLIVARIANA DE VENEZUELAMINISTERIO DEL PODER POPULAR PARA DEFENSA

UNIVERSIDAD EXPERIMENTAL DE LAS FUERZAS ARMADASPUERTO CABELLO EDO CARABOBO

HANDOUT Nº09

2.1.1 GeneralThe stability for the loading conditions defined in Pt B, Ch 3, App 2, [1.2.4] is to be in compliance with the requirements of Pt B, Ch 3, Sec 2.

2.1.2 AdditionalcriteriaIn addition to [2.1.1], the initial metacentric height is to be equal to or greater than 0,20 m.

2.1.3 Alternative criteria for ships greater than 100 m in lengthFor ships greater than 100 m in length, the Society may apply the following criteria instead of those in Pt B, Ch 3, Sec 2:

the area under the righting lever curve (GZ curve), in m.rad, is to be not less than 0,009/C up to an angle of heel of 30°, and not less than 0,016/C up to 40° or the angle of flooding f if this angle is less than 40°

the area under the righting lever curve (GZ curve), in m.rad, between the angles of heel of 30° and 40° or between 30° and f, if this angle is less than 40°, is to be not less than 0,006/C

the righting lever GZ, in m, is to be at least 0,033/C at an angle of heel equal to or greater than 30° the maximum righting lever GZ, in m, is to be at least 0,042/C the total area under the righting lever curve (GZ curve), in m.rad, up to the angle of flooding f is not to be less

than 0,029/C,

where:C : Coefficient defined by:

T : Mean draught, in m

KG : Height of the centre of mass above base, in m, corrected for free surface effect, not be taken as less than T

CB : Block coefficient

CW : Waterplane coefficient

D" : Moulded depth, in m, corrected for defined parts of volumes within the hatch coamings obtained from the following formula:

h : Mean height, in m, of hatch coamings within L/4 forward and aft from amidships (see Fig 3)

b : Mean width, in m, of hatch coamings within L/4 forward and aft from amidships (see Fig 3)

Bm, BD : Breadths, in m, defined in Fig 3

H : Length, in m, of each hatch coaming within L/4 forward and aft from amidships (see Fig 4).

Figure 3 : Definition of dimensions

Figure 4 : Definition of dimensions

2.1.4 Additional requirements for open top container shipsIntact stability calculations are to be investigated for the ship in the intact condition and considering the effect of the ingress of green water through the open hatchways in the following way:

for the intact condition described in [2.1.5] with the assumptions in [2.1.6], the stability of the ship is to comply with the survival criteria of Pt B, Ch 3, App 3: the factor of survival "s" is to be equal to one.

2.1.5 Loading condition for open top container shipsThe ship is at the load line corresponding to the minimum freeboard assigned to the ship and, in addition, all the open holds are completely filled with water, with a permeability of 0,70 for container holds, to the level of the top of the hatch side or hatch coaming or, in the case of a ship fitted with cargo hold freeing ports, to the level of those ports.Intermediate conditions of flooding the open holds (various percentages of filling the open holds with green water) are to be investigated.

2.1.6 Assumptions for the stability calculation for open top container shipsWhere cargo hold freeing ports are fitted, they are to be considered closed for the purpose of determining the flooding angle, provided that the reliable and effective control of closing of these freeing ports is to the satisfaction of the Society.For the condition with flooded holds relevant to the intact ship, the free surfaces may be determined as follows:

the holds are fully loaded with containers the sea water enters the containers and will not pour out during heeling, condition simulated by defining the

amount of water in the containers as fixed weight items the free space surrounding the containers is to be flooded with sea water the free space is to be evenly distributed over the full length of the open cargo holds.

Coast Guard issues safety alert after push boat fatalityThe Coast Guard says that recently a push boat operating "unfaced" (no barges attached) in the Houston Ship Channel flooded and sank while in the wake of a tractor tug resulting in the death of one push boat crew member and the narrow escape of two others. Although the investigation is not yet compete, it appears that the following occurred: The vessel's watertight doors leading to its engine room had each been pinned open. The push boat had very little freeboard and was fully loaded with fuel and water. As it took the wake of the tractor tug, the vessel listed to one side and down flooded the engine room through a watertight door. As it rolled to the other side, it took on more water, eventually sink stern first and coming to rest on the bottom of the channel in an upright position. A person working in the engine room was trapped by the incoming water and drowned. Two others narrowly escaped death after being trapped in a berthing area for over 10 minutes, breathing only a pocket of air before taking dramatic efforts to reach the surface via a broken window.

Watertight doors have been the subject of three other safety alerts involving fishing vessels and offshore supply vessels. Despite these awareness efforts, despite certain vessels having stability requirements requiring closure of such doors well documented in stability letters, despite owners and operators knowing what constitutes "Good Marine Practice," and many other applicable regulations the Coast Guard continues to investigate casualties where the failure to keep closed or properly maintain watertight doors is determined to be a causal factor.

Watertight doors function to establish the watertight integrity of the vessel and must always be treated as such. Although an open or poorly maintained door may seem like an insignificant issue, when the right causal factors align, the door can become a death trap and result in terrible circumstances to a vessel and its crew. The Coast Guard strongly recommends to all operators of any vessel, underway, having watertight doors

DRAW A DIAGRAM OF THE MIDSHIP CROSS SECTION OF A GENERAL VESSEL AND SHOW THE RELATIVE POSITIONS OF THE CENTRE OF GRAVITY, CENTRE OF BUOYANCY AND METACENTRE.

HANDOUT N º 10

Basic Principles of Ship PropulsionPageIntroduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Scope of this Paper . . . . . . . . . . . . . . . . . . . . . . . . . . 3Chapter 1Ship Definitions and Hull Resistance . . . . . . . . . . . . . . . . . . 4• Ship types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4• A ship’s load lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4• Indication of a ship’s size . . . . . . . . . . . . . . . . . . . . . . . . 5• Description of hull forms . . . . . . . . . . . . . . . . . . . . . . . . 5• Ship’s resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Chapter 2Propeller Propulsion . . . . . . . . . . . . . . . . . . . . . . . . . . . 10• Propeller types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10• Flow conditions around the propeller . . . . . . . . . . . . . . . . . . 11• Efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . · · · · 11• Propeller dimensions . . . . . . . . . . . . . . . . . . . . . . · · · · 13• Operating conditions of a propeller . . . . . . . . . . . . . . . . . . . 15Chapter 3Engine Layout and Load Diagrams . . . . . . . . . . . . . . . . . . 20• Power functions and logarithmic scales . . . . . . . . . . . . . . . . . 20• Propulsion and engine running points . . . . . . . . . . . . . . . . . . 20• Engine layout diagram . . . . . . . . . . . . . . . . . . . . . . . . . 22• Load diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22• Use of layout and load diagrams – examples . . . . . . . . . . . . . . 25• Influence on engine running of different typesof ship resistance – plant with FP_propeller . . . . . . . . . . . . . . . 27• Influence of ship resistanceon combinator curves – plant with CP_propeller . . . . . . . . . . . . 29