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Landing Craft, Tank, Air Cushion [LCTAC]

Landing Craft, Tank, Air Cushion (LCTAC) is a NAVSEA design initiative for a self-deploying, hybrid cushion/surface-effect ship landing craft. The design concept is for a relatively inexpensive vessel. It would use steel construction and diesel engine propulsion to reduce cost.

The current Navy/Marine Sea Basing program has pointed out the need for beachable reasonably high speed marine transports that are referred to as HSCs (High Speed Connectors). The concept behind Sea Basing is to have large supply ships positioned about 200 miles offshore with troops, supplies, vehicles, etc. transported to beachheads by the HSCs.

The LCAC (Landing Craft Air Cushion) is not only beachable but also amphibious. The LCAC is supported by a blower pressurized air cushion. The LCAC has a full 360 degree peripheral flexible skirt that attaches to the underside of its hull and restrains the air cushion between the hull and a water or land surface. The LCAC and its like are many times referred to as hovercraft. The LCAC has a number of inherent disadvantages, to wit: 1) It does not handle rough seas well, 2) It has an inherent rough "cobblestone" ride due to pressure perturbations in its air cushion where the pressure perturbations are mainly attributed to its full 360 degree flexible seals, 3) It is very weight sensitive, 4) It can only access beachheads that have gently sloped beaches, 4) Its full 360 degree flexible seals are expensive initially and to maintain, 6) Largely due to its need for power from three 4,500 HP gas turbines that supply propulsion and blower power, it is expensive initially with a current price of over $20 million, and 7) It is very noisy due to its necessary air propellers. In spite of these shortcomings the LCAC has been procured in reasonably large numbers due to its very valuable amphibious and 45 knot speed capabilities. The amphibious capability allows driving up onto a beach and discharging troops and cargo on dry land above the surf line.

The Navy LCAC landing and assault skirted hovercraft require large mother ships with internal loading ramps to service, load, and unload. The LCAC's poor lateral stability on or off cushion makes the loading of heavy units over the side of a cargo ship onto its deck a hazardous operation. Several of these large skirted hovercraft have flipped over attempting to operate in high wind and sea conditions. The excessive power required to operate these craft at high speeds reduces their effective range to short ferry boat operations.

The LCTAC concept is for a self-deploying landing craft with approximately five times the capacity of an LCAC and with comparable speed. The preliminary LCTAC design calls for 10,000 square feet of roll on/roll off vehicle storage (somewhat more than five times the vehicle area of an LCAC, and 40 percent of the vehicle area of an LPD-17). It would be able to transport 350 tons of payload (nearly five times the payload of an LCAC) at 30 knots over 1,000 nautical miles. Its unloaded range is projected to be 4,000 nautical miles, giving a significant capability for self-deployment.

As a hybrid air-cushion/surface-effect ship, it would not match an LCAC's ability to traverse beaches and operate on land. LCTAC distinguishes itself from the other alternatives by having the greatest load capacity and greatest capability for self-deployment.

For self-deploying LCAC alternatives, such as Landing Craft, Tank, Air Cushion (LCTAC), the key performance parameters are endurance and speed of advance (SOA). Capacity is less important because capacity shortfalls can be made up with additional landing craft.

Logical basing options for LCTAC vessels include Norfolk, Diego Garcia, and Guam. A self-deploying LCTAC based in Norfolk would need an SOA of more than 35 knots to maintain the performance of the 2005 program of record. Maintaining an SOA this high over distances exceeding 10,000 nautical miles is daunting. For LCTAC basing in Guam or Diego Garcia, the SOA requirement drops to somewhat under 30 knots to avoid slowing closure. LCTAC that could deploy with ESGs or self-deploy without slowing force closure offer the option of further reducing time to force closure beyond what could be achieved using MPSRON(F) ships to provide LCAC spots.



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Page last modified: 07-07-2011 12:47:42 ZULU