United States Navy Liferafts
In the United States, the US Coast Guard ensures the proper type and number of lifeboats are in good repair on large ships.
The United States Navy uses five types of custom inflatable life rafts as well as a number of commercially available Coast Guard approved life rafts. The 25-person MK-6 and 50-person MK-7 are used on surface ships, the 50-person MK-8 on aircraft carriers and LRU-13A and LRU-12A on aircraft and submarines respectively. Smaller combatant craft often use 6, 10 or 15-person commercial life rafts. The number of life rafts carried on USN ships is determined based on the maximum number of personnel carried aboard plus 10% as a safety margin. Aircraft carriers carry either 254 MK7 life rafts or 127 MK8 life rafts. While both are similar to heavy-duty commercial life rafts, USN life rafts use breathable air as the inflation gas rather than carbon dioxide to ensure full inflation within 30 seconds in Arctic environments.
Base material used on MK7 life rafts is polyurethane coated fabric which has very high durability. Old MK6 and a few MK8 life rafts are manufactured of neoprene-coated fabric, however, the majority of MK8 life rafts are also manufactured of polyurethane fabric. The lifeboat is compact and made of separate compartments, or tubes, as a redundancy against puncture. Two air cylinders containing dry, breathable compressed air provide initial inflation. Depending on the model life raft, each cylinder may contain up to 5000 psi of compressed air. Each life raft is equipped with an external, automatically actuated light beacon and internal lighting. Power is provided by lithium batteries.
USN life rafts are stowed in heavy-duty fiberglass canisters and can be launched manually or automatically should the ship begin to sink. Automatic launching and inflation is actuated by a change in pressure sensed by a hydrostatic release device should the ship begin to sink. A hand pump is provided to "top-off" pressure at night when temperatures drop and internal air pressure decreases. Relief valves are installed in each tube to prevent overpressure. Repairs to holes or rips up to six inches in length can be made using special sealing clamps. Occupants in USN life rafts are protected from wind, rain and sun by built-in canopies which automatically inflate. Hatches are sealable to prevent rain and seawater from entering the life rafts. Survival equipment includes: manual reverse osmosis desalinator (MROD), bottles of fresh water, individual food packets, fishing kit, signaling mirror, rocket and smoke flares, flashlight, spare sea anchor, first aid kit, paddles, spare batteries and bulbs, and aluminized mylar sheets ("space blankets") to aid in caring for victims of hypothermia.
USN inflatable life rafts are serviced every five years. Each life raft is test inflated before repacking. The USN life rafts have a high reliability rate of inflation.
Read more about this topic: Lifeboat (shipboard)
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