Advanced Marine Vehicleswith Focus on Hovercraft

Ahmed Hares Mohamed AdelKarim Kotb

Prof. Dr./ Mo’men Gaafary

Supervised by :-

Performed by :-

Ch. (1) Advanced Marine Vehicles

Table of contents

(Elements of Typical Hovercraft)

Ch. (2) Hovercraft

Ch. (3) Hovercraft

(Theory and Operation)

Ch. (4) Application of Hovercraft in Egypt

(Types & Characteristics)

(Case Study)

Advanced Marine Vehicles

Advanced Marine Vehicles, (AMV)

Contains a broad range of craft typesthese types were invented

to attain higher speeds at sea than

conventional ship types.

Two exceptions to this rule are :-

•The SWATHInvented to gain exceptional ride quality

among waves.SWATH : Small Water plane Area Twin Hull

•The HovercraftInvented to gain very special capability,

on sea & land surfaces.

There is an important principle in ship design, that goes something like

“Fast - Comfortable - Cheap” Pick Only Two

Recently, Naval Architectural Challenge isto balance between the following five parameters

• Speed & Power• Sea-keeping & Sea-kindliness • Comfort & Space• Load Carrying Ability• Economics

To Characterize the various AMV design concepts …

AMV – Types

What is Fast ? What is Speed ?

• Unfortunately, the answer depends upon size.

• It is important to begin by understanding the relationship between speed and size.

This small 20- knot Jet-Ski is clearly

fastThis 20- knot Washington State Ferry is

Slow

The answer lies in the naval architect’s tool of

“Froude Number.”

Froude Number is, crudely put,

“speed divided by size.”

The “size” can be length or displacement.

Two Particular Formulations are The Most Common :-

• “Length Based” Froude number .

FnL = V/ (g.L)^0.5

( is the most common in conventional ship )

• “Volumetric” Froude Number.

Fnvol = V/ [0.5 .g(Vol)^0.33]

( is useful in some high speed ship problems )

Going to a higher Froude Number requires more power

per ton of ship weight.

The NTUA-SDL FMV

Database Study

• 653 registered vessels • Froude number over 0.7

Brief about The AMV Types :-

•Monohull•Hydrofoil•Catamaran•Trimaran•SWATH•HOVERCRAFT*, or (ACV)

* Some Focus is given in Ch. 2 & 3

1) Monohull

• Round bilge semi displacement hull

• Planing hull, hard chine.

Round Bilge Hard chine

Low lift Higher lift

High resistance Lower resistance

Low acceleration

(better ride comfort ) Higher vertical acceleration

• These vessels are characterized by slender narrow hulls.

• The planing hull form is commonly used for Patrol Boats.

• A length to beam ratio of around 3:1

• Planing craft are generally small, say less than 40 meters.

• Hard chine superior for Fn > 2.25

• These vessels are high speed and high maneuverable.

Characteristics of Planing Hull

2) Hydrofoils

HOW IT WORKS ?

• At low speeds hydrofoils are totally submerged in the water.

• As the boat’s speed increases, the hydrofoils create lift.

• At a certain speed, the lift equals the sum of the boat and passengers weight. Therefore the hull comes out of the water.

Lift

Advantages

High cruising speed up to 50 kts

High level of comfort up to wave heights of 2.5 m

After dynamic lift, the drag decreases which leads to

a better use of power in increasing the speed.

Disadvantages

Limited payload capability, Large wing draft.

3) Catamaran

• The catamaran uses a very slender hull to get low drag , but it overcomes the stability problems by putting one of these hulls on each side .

• The speed range of all catamarans is about Froude Number = 2.0 .

.

• Disadvantages :-

.

The most important advantages of a catamaran over a mono-hull are :-

4) The Trimaran

.

• Trimarans are better than

Monohulls in minimizing Wave resistance by 53% , And catamarans by 19% .

Their overall advantages compared to monohulls are :

5) SWATH

.

.

The advantages of a SWATH

.

Seakeeping superior to similar-

sized conventional.

German shipyard Abeking & Rasmussen is the world’s most prolific builder of SWATH vessels

.

• SWASH

(Small Water-plane Area Single Hull)It uses a single submerged hull.

• ConceptFor rough waters .

Safe personnel transfer .

• Individual ParticularsSuperior seakeeping

Maneuvering capabilities

Low motion parameters

Length over all LOA 20.42 MBreadth Hull B 12.16 m Draught dmax 3.10 mSpeed Vmax 16.5 ktsMATERIAL aluminumControllable Pitch Propeller (CPP)

• Traditional propeller configurations have a tendency to cavitate at higher speeds. To maintain propulsion efficiency, designers have utilized a variety of propulsion packages including specially designed propellers,

• variable pitch propellers,

• surface drive outdrive units,

• Water jets

•

Hybrid vehicles combine more than one source of sustention or lift simultaneously.

The classification of advanced vehicles and their hybrid derivations usually follows :-

The classical sustention Triangle.

The "sustention triangle" is a commonly used forcharacterizing ship types.

The corners of this triangle represent the vessels supportedby :-

The edges and the inside of the triangle represent the hybrids.

The Hovercraft

Ch. 2

Elements of Typical Hovercraft…

What is a Hovercraft?

• A Hovercraft, also known as:-

An air-cushion vehicle, (ACV) is a craft capable of travelling overland, water, mud, sand, ice, or any combination of these surfaces.

A hovercraft is a vehicle that:-Flies like a plane, Floats like a boat, Drives like a car.

.

Invention

The first hovercraft SR-N1 by cockerel

SR-N1Used to transport soldiers

across English channel

Elevation, side view and plane

of the first Hovercraft SR-N1

• The principles of hovercraft operation is the use of

pressurized air to lift the hull off either the ground

or water surface.

• Normal atmospheric air is pushed into a plenum chamber by lift fans

and some parts of it escapes through a gap at the lower edge of the cushion.

• This volume of high pressure air is surrounded by a skirt, that prevents the pressurized air from escaping from the plenum chamber

The Principles of Hovercraft

Elements of Typical Hovercraft

•Hull

•Skirt

•Lifting fan

•Thrust fan

•Engine

•Control system

Hull

This is where the driver operates the hovercraft and where the passengers or cargo are located.

Types of Hull Material:-•Steel•Aluminum alloys•Magnesium alloys •Titanium

The fiber glass and composite materials, such as PVC which provide lightness, strength, and buoyancy in a single material.

Skirt

.

.

Major skirt design

Finger skirtBag skirt

Bag and finger skirt

Investigation of Skirt Dynamics under

Non-linear Wave Impact

A set of simulation

have been tested to investigate the

current results obtained reveal the

effect of the bag material stiffness

and bag thickness.

Water height 1(m)Water width 3(m)Wave-maker frequency 0.4(s)Wave-maker amplitude 0.5(m)

The Young’s modulus of the rubber ranges from 0.01~0.27 (GPa)

Results

The simulation is stable when Young’s Modulus is larger than 0.03 (GPa) with thickness of skirt of 40 mm or more

Lifting Fan

.

Thrust System

This consists of propeller or ducted fan that moves

air from front of the craft and accelerates it out

through the back.

This accelerated mass of air generates thrust which pushes the craft forward.

The Engine

A typical hovercraft uses one engine but larger sizes can use more

sometimes up six engines

Diesel engines are common but gas turbines are favor because this

type of engine is smaller and lighter for a given Horse power. And has

a higher weight to power ratio..

The engine should :-

Cause low noise

superb economy

electric start

air cooling and fantastic reliability

• Most hovercraft use two engines. One is used to lift the craft and the other engine is used for thrust.

• Some smaller craft use a single engine for both lift and thrust.

DE – Drive EngineDG – Drive GearboxLE – Lift EngineDLG – Distributing Lift GearboxLG1 – Lift Gearbox 1LG2 – Lift Gearbox 2

Propulsion Plant Configuration of Zuber class hovercraft

Full speed – 63 knots Full displacement – 500 tones

Control System

.

By means of moveable air ducts as the bow thrusters

The bow thruster can be swivel up to 180 degree from

their normal direction.

Advantages:-Enhance maneuverability

Theory & Operation ...

Ch.3

Hovercraft

Working Theory of Hovercraft

• In case of open plenum theory :

.

• In case of momentum curtain theory:

.

Operation of The Hovercraft

• Hovercrafts work on two main principles of lift and propulsion

• Lift fan allows the craft to ride on a cushion of air.

• Thrust fan moves air from front of the craft and accelerates

it out through the back.

• Hovercrafts have no contact with the ground.

Law’s Acts in Hovercraft

•• To lift the Air cushion vehicle, the pressurized air must push

against the surface of the water.

This law is sometimes referred to as the action-reaction law.

Aerodynamics is defined as the branch of fluid physics that studies the forces exerted by air or other gases in motion.

Lift CalculationTarget of This Study

1) To calculate the exit velocity of the air (Vexit) from cushion2) To calculate the flow rate of air escaping ( Q )3) To calculate the clearance between the lower

end of the skirt and the ground (h)4) To calculate the pressure inside the hull, Phull .

Pressure required inside the air cushion ( Pcu ) :-Pcu = F/A

Where,

F = is the load imposed by the hovercraft weightA = the hovercraft foot print

• According to Bernoulli’s equation,

Where

So that

Where,

Q = The flow rate of air escaping

h = The clearance between the skirt and the ground

L = Length of hovercraft

w = Width of hovercraft

Where:-

•Vexit is the exit velocity of the air •Dc is the discharge coefficient•ρair is the density of air

(1)

• To calculate the pressure inside the hull, Phull• The flow rate of air escaping

• The clearance between the lower end

of the skirt and the groundWhere,

X is the power of the engine

ηengine is the efficiency of the engine

ηduct is the efficiency of the duct

ηfan is the efficiency of the lift fan.

(2)

(3)

(4)

Drag Theoretical Approach

• The various components of drag, which apply to a hovercraft are as follows:-

• Wave making drag,

• Aerodynamic profile drag,

• Momentum drag,

• Skirt drag.

Where,

• 𝒑𝒄 is the cushion pressure

• 𝑺𝒄 is the cushion area

• 𝝆𝒔𝒘 is sea water density

• Fr is Froude number

• Lc is length of cushion

• Wave making drag

𝑫𝒘 = 𝟐 ∙ 𝒑𝒄𝟐 ∙

𝑺𝒄𝝆𝒔𝒘 ∙ 𝑳𝑪∙ 𝒈

∙ 𝟏 − 𝒄𝒐𝒔(𝟏

𝑭𝒓𝟐) 𝑫𝒂 =

1

2∙ 𝑪𝒂 ∙ 𝝆𝒂 ∙ 𝑺𝒂 ∙ 𝑽𝒔

2

Ca: is the coefficient for the aerodynamic profile dragits value is obtained from wind tunnel tests for detailed design.

Sa (Cushion Area): the frontal projecting area of the hull above the water Hovercraft's velocity.𝝆𝒂 : is the air density

• Aerodynamic profile drag

Where,

• Q is the cushion air flow,

• Vs is the speed relative to ambient air

• 𝝆𝒂 is the density of air .

The momentum drag is that force due to the rate of change of momentum of accelerating the cushion air and engine air to hovercraft velocity.

• Momentum Drag

𝑫𝒎 = 𝑸 ∙ 𝝆𝒂 ∙ 𝑽𝑺

Skirt drag is a function of Hovercraft size, shape, skirt design and cushion pressure.

• Skirt Drag

There is no adequate theoretical treatment for the skirt

Advantages of Hovercraft

1) Travel over any surface.2) Shortcutting routes.3) Travel Rivers up as fast as down, irrespective of the

current.4) Hovercrafts are very fuel efficient as Hovercraft do not

have to plough through the water but “fly” abovesurface.

5) At maximum speed fuel consumption of a Hovercraft is

about 70 % less than of a fast patrol boat

with similar payload capacity.

6) Access to 75% of coastal area instead of only 5% with conventional vessels.

7) Can be launched from ship.

8) Sea life and coral reefs remains untouched as Hovercraft propeller churns up the water .

•Disadvantages of Hovercraft

1) Potential of skirt damage/puncture.

2) They move a lot of air and can be relatively loud.

3) Steep grades can be issue.

4) Not exactly agile (e.g., cornering).

Modification and solution for the problems

FEA analysis indicated that a modification of the Design would correct the deformation

1. Skirt Damage problems

Recommendations and Solution for Noise Problem

NASA deals with this problem as follows:

1-The first generation of hovercraftThe distance between a terminal and

the nearest houses should be at least 800 yd

2-New generation of hovercraft• Reduction of the tip speed.

• Large numbers of blades and the use of devices such as shroud

rings are rejected

• Using aircraft soundproofing technique.

Why hovercraft?

Transport mode Maximum payload ( tons )

Speed ( knots )

Potential work capacity (ton . knots )

Maximum range (nautical miles)

Hovercraft 0.24 – 50.5 30 – 70 7 - 3280 60 – 310

Hydrofoil 1.3 – 23 32 – 48 40 – 897 145 – 300

Ferry 90 – 340 14 - 22 1260 - 7480 On cross channel

A comparison of some transport modes on a potential work capacity

Transport mode Lb of fuel required to transport 1 ton / mile

Hovercraft (amphibious) 2.3 – 3.7

Hovercraft (non-amphibious) 1.8

Hydrofoil 1.5 – 4.0

Fuel required to transport one ton of payload over one nautical mile

Future of The Hovercraft

•Hovercraft is the newest vehicle on Todays transport scene as well as being new, this vehicle is different from other, more conventional, terrestrial vehicles in that it requires no surface contact for traction.

Application of Hovercraft in Egypt Case study…

Ch.4

Application of Hovercraft in Egypt

1- Amphibious Army transportation mean at new Suez Canal region:

Suez Canal characteristics:

• The total length is 193 km from Port Said to Suez.

• The depth is 24 m .

• The width ranges from 280 m to 345 m.

New Suez Canal Characteristics:

• The total length is 72 km , 35 km dry digging & 37 km deepening the waterway.

• The sand island width ranges between (500 to 1684) m approximately.

لبعد عن البحيرات اعدد قنوات االتصال

المرة

العرض الطول

قناة االتصال

االولي8.1521.679.4

قناة االتصال

الثانية11.6598.2131.1

قناة االتصال

الثالثة20.11684.3124.5

قناة االتصال

الرابعة30.4813.193.5

Application Of Hovercraft In EGYPT2-As a fast ferry between EGYPT & SAUDI ARABIA :

THE HOVERCRAFT IS THE BEST ALTERNATIVE TO THE BRIDGE

Using a Hovercraft between “ Lara ” region in EGYPT & “ Sheikh Humaid ” region in SAUDI.

The distance between them is about 20 km .

• This will save about 12 hours for travelers by land in the way of Nuweiba & Aqaba.

2007

Application Of Hovercraft In EGYPT3-As a fast ferry between Hurghada & Sharm EL-Sheikh :

• The distance between Hurghada and Sharm EL-Sheikh through the RED SEA is about

110 km.

Merits of using Hovercraft ferries in Red Sea

• Sea life and coral reefs remains untouched as Hovercraft propeller churns up the water .

Application Of Hovercraft In EGYPT4- Used for tourism purposes

Region : Lake Nasser

Target : To transfer tourists to and from the floating Hotel

Application Of Hovercraft In EGYPT

5-Land and maritime rescue in case of storms and floods:

• manager of the maritime rescue and environment protection organization of RED SEA confirms the need of Hovercraft to save people’s lives.

All References are under Request…

MKA Team at Ismailia City