11/04/2002container ships1/43 lecture layout definition developments of container ship concept...

11/04/2002 Container Ships 1/43

LECTURE LAYOUT

• Definition

• Developments of container ship concept

• Aspects of container ship design

• Main dimensions: length, breadth, depth, draft

• Containers

• Container stowage and securing

• Hullform

• Stability


DEFINITION

• Containerisation can be considered as a total transportation concept.

• The cargo is handled in a utilised form suitable for carriage by sea, road, rail and inland waterways.

• Container ship is the seaborn link in the chain.

• Containerisation offers a true door to door service.


DEVELOPMENT OF CONTAINER SHIP CONCEPT

• The first container ships were converted from tankers to carry unitised cargo.

• After the developments container ships became• complex,

• highly specialised vessels

to maximise the benefits to be gained from high cargo handling rates and reduced port time.



• The design philosophy has changed from its early form because of:

• the changes in the world economy

• changes in the trading pattern,

• major world political events.



• The first container ships had low carrying capacity, because the origin ships were designed to carry bulk cargoes.

• The development of specialised container carrying vessels resulted in increases in container capacity for a given volume.



• The first ships were carrying around – 1200 TEU (twenty-foot equivalent units) – with the service speed 22 knots.

• The first large container ship were designed in the late 1960’s.

• The size and speed of the ships increased to take the advantage of the economy.



• The large ones upto – 3000 TEU – were powered by twin or triple screw steam or diesel

plant – to give service speed of around 26 knots.

• After a number of years of successful operation these vessels were badly hit by rising fuel coasts.



• Many of the vessels were re-engined to single screw diesel plant.

• The reduction in speed resulted in – fuller forms – with the associated advantage of the vessels being

able to carry • required capacity with much reduced main dimensions.


ASPECTES OF CONTAINER SHIP DESIGN

• A container ship can be • a pure container carrier,

• a container/RoRo carrier,

• a general cargo vessel with a container carrying capability.

• A container ship can carry:• a cargo handling equipment or not.



• The cargo securing equipment can be different types.

• Modern cargo vessels have container carrying facility but restricted by:

• small hatch area/deck area ratio,

• deck stowage resulted from stability consideration,

• relatively low ballast of vessels can be another restriction.



• The design of pure container ships is based on the cargo unit to be carried.

• The dimensions, hullform and general layout being developed to maximise the capacity.

• Different cargo securing equipment are used to minimise the risk of cargo damage or loss.



• A pure container vessel can be a• deep sea vessel,

• feeder vessel to provide a container distribution service

• A modern deep see vessel has a capacity of – 2500+ TEU – with a service speed of 18-24 knots.

• Feeders have the smaller capacity – around 500-1000 teu– 16-18 knots.



• The large vessels operate on well defined liner route with land based cargo handling equipment.

• On the other hand feeders are usually operate between the ports without proper shore based equipment, so have cargo handling equipment.


MAIN DIMENSIONS

• The main dimensions of container ships are based on the physical size of the containers to be accommodated.

• For a specified container capacity, the dimensions of the vessel will be determined by the number of bays, rows and tiers.

• Dimensions also depend on the navigational futures such as the Panama canal etc.


MAIN DIMENSIONS


LENGTH

• Length of a container ship can be calculated by adding:

• length of the cargo space,

• length of the machinery space,

• length of the fore peak space,

• length of the aft peak space.


LENGTH


LENGTH

• The length of the cargo space is a function of:• number of container bays,

• the length of the containers,

• required clearances to accommodate the container securing device,

• necessary allowance for structural members should be taken into account.

• Cargo handling equipment such as cranes should be

calculated in cargo space length.


LENGTH

• For preliminary design work, it can be assumed that the length required for each container is (l+1.5) m where l is length of a container (Munro-Smith, 1975) by making allowances for clearance and cross-ties. The LBP of the ship is the sum of the container portion, engine-sterntube and portion forward. Thus:


LENGTH

LBP = Lc + Le + Lf + LBCC

where Lc = Container portion = Nx.(l+1.5)

Nx = Number of containers in the length.

Le = Length of engine room and after peak tank

Lf = Length of fore peak tank.

LBCC = Length between most forward cargo hold and collision bulkhead.


LENGTH

• As a first approximation

– the length of the aft peak tank can be taken as 3.5% of LBP.

– The length of fore peak tank can be taken as 5% LBP and

– length of space forward of container length can be taken as 10% LBP.

LBP=0.035 LBP+Le+LC+0.1 LBP+0.05 LBP


BREADTH

• Breadth is a function of the size of the container units and calculated using the number of container rows.

• The gaps between containers depend on the type of stowage equipment.

• Breadth is very important to the stability. It is great concern in the design and operation of container ships then any other vessel type.


BREADTH

• Containers have a standard width of 2.43 m. However, each container requires an allowance for clearance, guides, etc. of about 240 mm (Munro-Smith, 1975) so that each container requires a width of 2.67 m. Thus the number of rows (Ny) cells located transversely in the ship require 2.67 Ny m. Since the width available for containers is about 80 percent of the ship's breadth B, then


BREADTH

0.80 B = 2.67 Ny

B = 3.34 Ny

Ny : Number of tiers of containers in holds.


BREADTH


VISION


DEPTH

• It is a function of the size of the container unit with the vertical gaps between the adjacent containers and the height of the tank top in the holds.

• The number of tiers of containers to be carried in the hold will be dependent on the proportion of the total capacity of the vessel to be carried under the deck.


DEPTH

• The rate of under container numbers is around 40-60 % of the total capacity.

• Container ships are associated with large freeboard and light loaded drafts.

• The light draft is due to the low density of the cargo .


DEPTH

• This results low displacement according to the physical size of the vessels.

• Container ships are deep vessels to accommodate the under deck stowage results in the large freeboard.


DEPTH

The depth of the ship is in generally controlled by the number of containers to be carried vertically. Thus:

D=Nz H + DB where

Nz = Number of tiers of containers in holds

H = Height containers

DB = Depth of double bottom.


CONTAINERS

• The most common container sizes are 20 and 40 foot ISO standard containers.

• There are some other container sizes which are not commonly used.

• The problem of the container ship design occurs if the different size of containers should be carried.


CONTAINERS


CONTAINER STOWAGE AND SECURING

• In the holds usually cell guides system is used for stowage and securing.

• The system reduces the chance of container damage and speeds up the loading and unloading process.



• A typical cell guide system consists of groups of four vertical guides constructed from steel angle bars into which the containers are lowered running the full depth of the vessel from hatch coaming level down to the top tank.



• The tolerance into the guides must be small thet shifting of the containers is minimised and that the container spreader can be easily engaged when removing containers.

• With this system fastening of the individual containers is unnecessary as all of the static and dynamic forces generated by the containers are transmitted directly into the ship structure by the cell guide members.



• There are leading equipment on top of the cell guides in both the longitudinal and transverse directions.

• The above deck containers are affected by static and dynamic forces.



• These forces limit the securing equipment and number of tiers usually 3 or 4 tires are used.

• Twist locks and lashing roads are commonly used above deck securing equipment.


HULLFORMS

• Afterbodies of container ships are generally characterised by wide transom stern which provide aided stability, increased hold volumes and increased deck areas.

• This increases in powering due to large wetted surface area, hence frictional resistance and the increased tendency to slam.


HULLFORMS

• Another disadvantage of this, flat sections above the propeller will cause vibration.

• The fore body will have a bulb to promote the cancellation of the bow wave. This reduces wave making resistance.

• Fore body will usually be V shaped in order to improve stability and increase deck area and underdeck container capacity.


STABILITY

• The stability of container ships is perhaps the most important aspect of their design.

• Vertical centre of gravity is very high because of above deck containers, therefore container ships have to be operated with some amount of ballast.

• In order to minimise the amount of ballast the heavier containers can be carried in the bottom tiers and the lighter or empty ones being carried on-deck, then VCG is reduced.

11/04/2002container ships1/43 lecture layout definition developments of container ship concept...

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