DESIGN OF VEHICLES USED

FOR AMPHIBIOUS OPERATIONS

Presented By Onkar Madhukar Thite

INTRODUCTION:

Lifts the armed forces and deploys them far from its natural borders.

They carry troops and other armoured vehicles and their crew.

Very important in tactical warfare and deploying forces in carrying out supreme attacks.

Also used in rendering assistance to civil authorities at the time of natural calamities.

TYPES OF AMPHIBIOUS VESSELS

• Landing Platform Docks (LPD)• Landing Air Cushion Vehicles (LCAC)• Landing Ship Tank (LST)

• Medium (M)• Large (L)

• Landing Craft Unit (LCU)• Landing Craft Assault (LCA)

Initial estimates

-Type of ship (Class)-Displacement-Electrical load-Switch board-Tank capacities-Main Dimensions and form

parameters

Major Design Considerations

- Tactical influence- Wading depth / Beach

Gradient- Hull form for shallow draft

Characteristics features

-Tank hold arrangements• -Arrangement for trucks• -Helicopter landing facilities• -Bow door and Bow ramp• -Machinery and stores• -Water tight integrity

GENERAL SHIP SYSTEMS

• -Air conditioning systems• -Ventilation• -Salt water systems• -Fire fighting systems• -Ballasting and deballasting systems• -Prewetting systems• -Fuel oil systems• -Sewage treatment plant• -Fresh water systems

• PREWETTING SYSTEM: A deck washing line is provided all over the exposed portions of the ship. This system provides sea water for washing away any nuclear, biological, or chemical products of a NBC attack. Sea water is taken from salt water main through control valves. Prewetting nozzles are provided for this purpose on the weather deck and the superstructure.

-Factors governing the forward draft at the time of beaching

• Wading depth• Ramp length• Ship’s displacement• Tidal conditions

TACTICAL INFLUENCES• a) Landing troops, freight and, vehicles on

to a beach.

• b) The conveyance of troops, freight and vehicles through water.

DEPTH• a) The requirement to have the smallest

mean draft possible to allow the operation in very shallow water.

• b) Military operations require the landing of tanks and other wheeled vehicles having a wading depth of approximately one meter, on to a beach with an assumed gradient of 1:40. The Wading depth of the vehicles determines the forward draft of the vessel.

LENGTH AND BREADTH

• c) The length required to arrange the tanks, other wheeled vehicles, the flight deck etc. together with the length of the engine room, auxiliary engine room (if any) and the steering gear compartment determine the length of the vessel.

• d) The minimum beam is determined by the arrangement of vehicles and the troops accommodation. The size of the building berth also influences this parameter.

HULL FORM GENERATIONS

- Operates in shallow waters• - Flat keel for beaching• - Obtuse bow• - Long parallel middle body

WADING DEPTH:

• The forward draft of the vessel must be small enough to allow the military vehicles to be discharged on a beach of gradient 1:40. Steeper beaches will be a bonus and of course lessen the actual distances to be waded. They also lessen the wading depth in certain circumstances.

FLAT BOTTOM BOX SHAPE HULL

To obtain a reasonably shallow draft, it is necessary to have a flat, box shaped hull.

flat bottom has the advantage for a landing vessel when it has to sit on the bottom.

The flat bottom, box shaped hull will give additional buoyancy to the hull, thus reducing the draught

DISADVANTAGES• The sea water intakes on the bottom are

closer to the sea bottom due to the shallow draught. This sucks in the mud from the bottom.

• Flat bottom also makes it susceptible to damage due to grounding.

provide a design trim by the stern

• It gives a lesser draught at the forward end

• ensures that the ship does not trim by the bow in any normal sea going conditions

• it gives the required clearance for the propeller from the keel line.

But there is limit for the design trim which can be provided from the operational point of view the effect is an increase in resistance. There is

also the increased risk of stern touching the beach before the bow

reducing the forward draught is by trimming the ship by stern, as and when required

at the time of beaching . This is achieved by the judicious distribution of the weight along

the length of the ship.

To demonstrate an acceptable degree of safety of the ship, the stability of the ship was

assessed as per Stability criteria for warship (NES 109)

• Cases listed below were considered • -high speed turning• -effect of wind• -lifting of heavy weights particularly over

the side• -crowding of personnel to one side• -bow collision• -weapon damage

side loading in olden days ships is avoided

Due to the unusual hull form of the ship, resistance prediction has a lot of serious

problems

• Resistance estimation by standard program is not valid for LST

• Series data applicable for such hull form, with high B/T ratio and Cp are not available.

• Since the new design does not have an exact parent ship, the method of interpolating from the parent ship data was also not applicable.

PropulsionLST being a shallow draught vessel, the propeller diameter is restricted, mainly due to the following factors:

• - Clearance between hull and waterline from the propeller tip.

• - Clearance of the propeller blade tip above the keeline, from beaching considerations.

GENERAL ARRANGEMENT• a) Tank hold for the arrangement for tanks

and their embarking and disembarking facilities.

• b) The arrangement for trucks on the weather deck and their embarking and disembarking facilities.

• c) Helicopter landing facility• d) Bow door and bow ramp

BOW DOOR AND BOW RAMP

• To allow the embarking & disembarking of the vehicles to and from the ship, bow door and bow ramp are to be provided in the forward end of the ship. These are hydraulically operated and are watertight integrity of the ship. The system comprises of outer shell doors, in two halves, formed to the shape of the stern and a three section ramp. The control of the whole system should be both, local and remote from the bridge

ANCHORING SYSTEM

• Kedge anchor assists in the beaching operation and the retraction of the ship from the beach. This anchor along with Dankforth anchor which is fitted at the aft of super structure on the main deck.

Amphibious Vessels for the Indian Navy

• L-20 INS Magar LST(L)• L-23 INS Gharial LST(L)• L-14 INS Ghorpad LST(M)• L-17 INS Sharabh LST(M)• L-18 INS Cheetha LST(M)• L-32 to L-39 LCU’s

US to sell India its Austin-class LPD

• . Presently, the most capable ship that the Indian Navy possesses for amphibious operations is the 3,600-ton Magar-class Large Landing Ship Tank (LST-L). It can carry up to 500 troops, 15 tanks and 8 Armoured Personnel Carriers (APC). It can also operate two medium-lift helicopters, which are primarily meant for 'inserting' a small team of Special Forces (marine commandos) with conventional beaching system. In contrast, a LPD like has carrying capacity roughly double that of the LST-L and it has a greater endurance of 7,700 nautical miles at a speed of 20 knots, as opposed to the LST-L's 3,300 nm at 14 knots. More importantly, it has a large platform to operate up to six medium-lift helicopters and a floodable 'well-deck' at its stern for housing smaller landing craft or hovercraft. This implies that a LPD does not need to 'beach' to discharge its personnel and cargo.

References• Surface Warships’ P J Gates• ‘Amphibious vessels – A literature

survey’ – Lt S B Anandan• ‘Considerations in landing ship design’

- Lt J F Vellara

QUESTIONS