Defence Industry

Trends in Design of Amphibious Warfare Ships
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Issue Vol. 29.1 Jan-Mar 2014 | Date : 09 Feb , 2014

In the Indian Navy’s recently released RFP, though the ship is termed as a LPD, the specification requires a “through” flight deck, with a below deck hangar, akin to what is normally termed as a Landing Ship Helicopter Dock (LHD). It would be instructive to compare the IN’s key requirements, i.e. in respect of size, speed, payload and amphibious assets with those pertaining on contemporary modern LHDs. Comparison will be made with the French “Mistral” class, designed by DCNS, and the Spanish “Juan Carlos 1” designed by Navantia, as in the table (Ref 1-5) above :-

Speed, size and sea keeping requirements mandate a conventional mono-hull design…

The foregoing comparison indicates that the IN’s requirements are, in general, of the same order as those of current proven designs. The technical risk in evolving a successful design meeting the IN’s requirements would, therefore, be minimal. Although the comparison has been restricted to ‘through deck’ ships, the traditional LPD type concept, with a superstructure located forward, large helo deck located aft and a stern well-dock, is an equally valid option for naval planners, depending on their requirements, and continue to be built, the US Navy’s LPD-17 class being a notable example.

While finalising the design of the amphibious warship, the selection of the ‘ship-shore connecter’ is a critical factor. The amphibious force could well arrive at the stand-off point undetected, at the planned time but unless it is capable of delivering the heavy equipment of the embarked amphibious force, from the stand off point to the beach, in the shortest possible time so as to achieve the required concentration of force, success may be elusive. Approaching the beach edge requires traversing shallow water, for which, flat bottomed, rectangular ‘shoe-box’ shaped landing craft, generically termed Landing Craft Mechanised (LCM), equipped with a ramp at the forward end, have been in use since the WW II era. These craft are slow, and do not ride well in a high sea state that can obtain at the stand-off point. Their carrying capacity is limited, and when fully loaded, the draft increases and prevents them from reaching the water’s edge, precluding ‘dryshod landing’ for personnel and vehicles, increasing their vulnerability.

Air cushion vehicles, such as the Landing Craft Air Cushion (US LCAC), built by Textron Marine and Land Systems, overcome the limitations of the landing craft, in terms of speed and they are able to disembark their loads beyond the shoreline.

Fig-6 US Navy LPD USS San Antonio

However, they are several orders of magnitude more expensive than water-borne craft and their operation requires special arrangements, posing limitations:-

  • Special ventilation arrangements are required in the well deck to control the temperature rise when LCAC engines (aero gas turbines) are operating.
  • Vehicles are required to reverse into the LCAC, in order to drive out ‘forward’.
  • Loads need to be carefully balanced as in an aircraft, requiring precise positioning of vehicles.
  • The LCAC needs to be inspected for loose/foreign objects prior to starting engines, to prevent FOD, increasing preparation time.
  • For carrying a high number of personnel, a special ‘personnel transport module would need to be erected for safety, which is time consuming and reduces flexibility.
  • The LCAC would not reverse in its approach track to the beach, but requires space on the beach to turn around.
  • Specially trained maintainers (upto ten) need to be embarked, as requisite skills would not be available with the ship’s crew.

Fig-7: Landing Craft Air Cushion (LCAC )

Despite its advantages over the traditional LCMs, it is not surprising that besides the US Navy, it is in service only with the Japan Maritime Self Defence Force.

Efforts to develop a ship-shore connecter, which provides performance comparable or better than the LCAC, without the attendant limitations of the latter, and with a substantially lower price tag have resulted in the development of the Landing Catamaran (L-Cat) by the French firm Constructions Industrielles de la Mediterranee (CNIM)). This innovative craft has a ‘variable shape’ hull form.

Fig-8 Spanish LCM 1E (the latest development in conventional LCMs)

The catamaran comprises two narrow hulls, housing the propulsion plant, conning positions, tanks and other ship systems. A pontoon type ‘loading platform’ is suspended between the hulls, on hydraulically operated jacks, which can raise and lower the platform. Ramps are fitted at each end of the loading platform, which provide ro-ro capability, enabling vehicles to be loaded as well as disembarked while driving ‘forward’, thereby cutting down on the turnround time. When operating in deep water, the platform is raised, and the catamaran hulls provide a stable ride at high speed due to their low resistance. For beaching and for entering the stern dock of the mother ship, the pontoon is lowered and forced downward, into the water. The buoyancy of the pontoon causes the twin hulls to ‘rise’ out of the water, thereby reducing the draft of the vessel, and enabling the forward ramp to touch down on the dry beach surface.

Fig-9: LCat/E-DAR underway in catamaran mode

The unique features of the LCat are:-

  • High load carrying capacity, 80 tonnes normal and 100 tonnes maximum vs 54 tonnes of LCM 1E and 60 tonnes of the LCAC
  • High speed 30 knots light and 18 knots loaded vs 22 knots light and 13 knots loaded of LCM 1E.
  • High maneuverability can turn on its axis at low speed and can ‘slide’ laterally.
  • High power of four water jets enable craft to pull away from the beach without using the kedge anchor, and enable it to maintain position on the beach in cross wind conditions.
  • Capability of landing at waters edge on beaches gradient as low as two per cent.
  • Capable of loading/unloading vehicles by deploying own ramp on the well deck sill of the mother ship without having to enter the dock dramatically reducing turnround time between shuttle trips.
  • Low cost (both, initial and through life) as compared to the LCAC, with a higher ‘per day’ throughput rate.

Fig-10: LCat/E-DAR disembarking armoured vehicles at water’s edge

The French Navy has commissioned four LCats, which have been given the nomenclature “EDAR”, and has an option for four additional craft. Other potential buyers have also shown interest. Other than being unable to traverse across land, its performance surpasses that of the LCAC and conventional LCMs, especially for stand off beaching operations, due to its high payload, high speed and lower turn-round time. It can operate from any suitably sized well dock, without any special arrangements having to be made. For operating the LCAC, the mother ship needs to have special ventilation arrangements in the well deck to control the rise in temperature caused by the running of the LCAC’s engines. The L-Cat therefore allows navies to complement their modern and capable amphibious warfare ships with an extremely efficient and effective ship-shore connecter, greatly enhancing their amphibious capability. It is relevant that the RFP issued by the Indian Navy, requires the well dock to be capable of accommodating two LCats.

The LCAC 100 is expected to have improved payload, speed, fuel efficiency and reliability…

Looking into the foreseeable future, amphibious operations would continue to remain a valid option for military planners, because the oceans connect the world and allow the deployment of amphibious forces in locations of ones choosing, with the ability to project power into the hinterland as demanded by the situation. They are often the only option for providing succour in times of natural disasters. Technological advances can be expected in both, amphibious ships and their ship-shore connecters.

A greater stress on increasing the integral aviation capability could be expected, by way of increased number of embarked helicopters as well as capability to operate tilt rotor craft. Depending on the affordability and availability of STOVL aircraft, incorporation of ski jumps on flight decks could more frequently specified. Stealth features would be incorporated into designs to a greater extent, as seen on the LPD-17 class. Development of ship-shore connecters is expected to continue apace. The LCAC 100 is expected to have improved payload, speed, fuel efficiency and reliability and there are indications that it would be supplied to the US Navy around 2019. However, its cost would probably be a deterrent to non-US users. Developments of the L-Cat, including a larger version for autonomous operation, independent of the mother ship, are also in the offing. These and other developments would continue to engage the attention of naval planners over the world.

References

  1. “Shape of Things to Come: Spain’s New Projection Ship Readies For Sea”, Nick Brown Jane’s IDR, Oct 2009 pp 70 -75
  2. “Amphibious Assault and Power Projection Platforms”, Massimo Annati, Military Technology, 11/2007, pp 64 – 73
  3. “France’s Amphibious Renaissance Adds Weight to Naval Power Projection”, Richard Scott, Jane’s IDR, Dec 2011, pp 52 – 56
  4. “Shipping New Challenges”, ER Hooton, Armada International, 5/2005, pp 19-24
  5. http://www.defensenews.com/article/20131212/DEFREG03/31212003
  6. http://wikipedia.org/wiki/Landing_Craft_Air_Cushion
  7. Data on LCat, courtesy CNIM.
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