Liferafts in general are collapsible, and stored in a heavy-duty fiberglass canister, and also contain some high-pressure gas (in commercial models, usually compressed air) to allow automatic inflation to the operations size. SOLAS and military regulations require these to be sealed, never opened by the ship’s crew; they are removed at a set periodicity (annually on merchant vessels) and sent to a certified facility to open and inspect the liferaft and contents. In contrast, a lifeboat is open, and regulations require a crew member to inspect it periodically and ensure all required equipment is present.
Modern lifeboats have a motor; liferafts usually do not. Large lifeboats use a davit or launching system (there might be multiple lifeboats on one), that requires a human to launch. Lifeboat launching takes longer and has higher risk of failure due to human factors. However lifeboats do not suffer from inflation system failures as inflatable liferafts do.
Recently,[when?] smaller self-rescue lifeboats have been introduced for use by boats with fewer people aboard: these are rigid dinghies with CO2-inflated exposure canopies and other safety equipment. Like the lifeboats used before the advent of the petrol engine, these self-rescue dinghies are designed to let the passengers propel themselves to safety by sailing or rowing. In addition to their use as proactive lifeboats, these self-rescue dinghies are also designed to function as unsinkable yacht tenders. See photo of proactive lifeboat above.
The International Convention for the Safety of Life at Sea (SOLAS) makes it a requirement for merchant ships to have liferafts on each side of the ship, sufficient for all the people on board (the stated capacity of the lifeboat, irrespective of the fact that there may actually be fewer people on board). However, if the lifeboats are “easily transferable” (viz. have an open deck between port and starboard lifeboat decks), the number of liferafts may be reduced to a total sufficient for the ship’s capacity.[clarification needed]
The equipment carried in a liferaft is much less than a lifeboat. Vis a vis lifeboats, liferafts are not self-righting and have no motor.
Freefall lifeboat of the Spring Aeolian
Some ships have freefall lifeboats, stored on a downward sloping slipway, dropping into the water as holdback is released. Such lifeboats are considerably heavier as they are strongly constructed to survive the impact with water. Freefall lifeboats are used for their capability to launch nearly instantly and high reliability in any conditions, and since 2006 are required on bulk carriers that are in danger of sinking too rapidly for conventional lifeboats to be released.
Tankers are required to carry fireproof lifeboats, tested to survive a flaming oil or petroleum product spill from the tanker. Fire protection of such boats is provided by insulation and sprinkler system, which has a pipe system on top, through which water is pumped and sprayed to cool the surface. This system, while not failsafe against engine failure, allows fireproof lifeboats to be built of fiberglass.
Vessels that house saturation divers carry hyperbaric lifeboats which incorporate ahyperbaric chamber to allow the divers to escape without undergoing decompression.
A rigged WW II airborne lifeboat in front of a Vickers Warwick from which it would be dropped to survivors on parachutes.
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 osmosisdesalinator (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.