A lifeboat is a small craft carried on a ship to provide a means of emergency evacuation in the event of a disaster aboard the ship. Lifeboats may be rigid or inflatable vessels; the inflatable type are sometimes referred to as liferafts. In the military, a lifeboat may be referred to as a whaleboat, dinghy, or gig. The ship's tenders of modern cruise ships are often designed to double as lifeboats and "lifeboat drills" are a part of the cruise experience.
Inflatable lifeboats may be equipped with auto-inflation (carbon dioxide or nitrogen) canisters or mechanical pumps. A quick release and pressure release mechanism is fitted on board ships so that the canister or pump automatically inflates the lifeboat, and the lifeboat breaks free of the sinking vessel. Commercial aircraft are also required to carry auto-inflating life rafts in case of an emergency water landing, and are also kept on offshore platforms.
Ship-launched lifeboats are designed to be lowered from davits on a ship's deck, and are unsinkable, with buoyancy that cannot be damaged. The cover serves as protection from sun, wind and rain, can be used to collect rainwater, and is normally made of a reflective or fluorescent material that is highly-visible. Lifeboats are usually equipped with flares and/ or mirrors for signaling, several days' worth of food and water, basic first aid supplies and oars. Some lifeboats are even more capably equipped to permit self-rescue; containing such supplies as a radio, an engine and/ or sail, heater, basic navigational equipment, solar water stills, rainwater catchments and fishing equipment.
The International Convention for the Safety of Life at Sea (SOLAS) and the International Life-Saving Appliance Code (LSA) require a specific list of emergency equipment to be carried on each lifeboat and liferaft used on international voyages. Modern lifeboats should also carry an Emergency Position-Indicating Radio Beacon (EPIRB) and either a radar reflector or Search and Rescue Transponder (SART). In the United States, the US Coast Guard is responsible for making sure that the proper type and number of lifeboats are available and kept in good repair on any large ship.
By the turn of the 20th century larger ships meant more people could travel, but safety rules in regard with lifeboats stayed out of date- for example, British legislation concerning the number of lifeboats was based on the tonnage of a vessel and only encompassed vessels of '10,000 gross tons and over'. It was after the sinking of the RMS Titanic on April 15, 1912, that a movement began to require a sufficient number of lifeboats on passenger ships for all people on board. The Titanic, with a gross tonnage of 46,000 tonnes and carrying 20 lifeboats, met and exceeded the regulations laid down by the Board of Trade, which required a ship of her size (i.e. over 10,000 tons) to carry boats capable of carrying a total of 1,060 people. The Titanic's boats had a capacity of 1,178 people on a ship capable of carrying 3,330 people.
The need for so many more lifeboats on the decks of passenger ships after 1912 led to the use of most of the deck space available even on the large ships, creating the problem of restricted passageways. This was resolved by the introduction of collapsible lifeboats, a number of which (Berthon Boats) had been carried on the Titanic.
Liferafts in general are collapsible, and stored in a heavy-duty fiberglass canister, and also contain some high-pressure gas 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 and sent to a certified facility to open and inspect the liferaft and contents. In contrast, a lifeboat is open, regulations require a crewmember to inspect it periodically and ensure all required equipment is present. Modern Lifeboats have some form of a motor; liferafts usually do not have a motor. Lifeboats require some form of a davit or launching system (there might be multiple lifeboats on one), and that does require human intervention to commence or be involved in the launch process. Thus, launch of lifeboat is longer and has higher risk of failure due to human factor, however, lifeboats don't suffer from inflation systems failures like liferafts.
Some ships have freefall lifeboats, stored on a significantly downward sloping slipway, dropping into the water as holdback is released. If launched, return to the launching system is only possible at a pier using a large crane, and such lifeboats are considerably heavier to survive the impact with water. Freefall lifeboats are used for their capability to launch nearly instantly and high reliability, 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 pipe system on top, through which water is pumped and sprayed to cool the surface. This system, while prone to engine failure, allows fireproof lifeboats to be built of fiberglass and not only metal.
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.
Any small self-contained spacecraft designed to operate as a life-preserving vehicle or escape pod for the crew of a spacecraft in distress might also be termed a "lifeboat", and this usage frequently appears in science fiction.