A liferaft, also written life raft, is a floating survival craft that takes people aboard after they leave a ship or aircraft and keeps them out of the water as far as possible. Buoyancy bodies support occupants and equipment; a canopy, where fitted, reduces exposure to wind, spray and sun. For isolated personnel, the raft combines protection at the surface with the ability to stay together, use available survival equipment and support their own detection.
Buoyancy and protection
In an inflatable raft, gas-tight tubes form the load-bearing perimeter. Their volume displaces water and produces the buoyancy that supports the load. A gas cylinder fills the chambers when the inflation mechanism is operated; carbon dioxide and nitrogen are examples of inflation gases. Non-return valves retain gas in the individual chambers. Separate chambers limit the consequences of a single puncture: a hole in one tube then does not empty the others as well. The load that the remaining buoyancy bodies can support is a property of the particular design. The reserve buoyancy of a multiple-chamber marine raft cannot be transferred to every small aviation raft. Rigid liferafts instead obtain buoyancy from built-in inherently buoyant bodies.
The floor supports people above the surrounding water. An insulating floor layer or additional inflatable floor reduces heat loss towards the cold water surface; some floors require separate inflation with the bellows carried in the raft. The canopy excludes rain and spray, reduces wind exposure and provides shade. Its openings must also allow ventilation. Water inside and soaked clothing can continue to cool occupants even under a closed canopy. A canopy without floor insulation therefore provides different protection from a fully protected design.
Other components address specific problems. A boarding ramp or ladder helps a person cross the high buoyancy-tube edge. External lifelines provide handholds for people in the water; internal lines help occupants hold their position in a seaway. Ballast pockets beneath the raft fill with water. They increase the mass moved and water resistance against rapid changes of attitude, helping stabilise the raft. A drogue, or sea anchor, creates drag in the water, damps movement and reduces wind drift. It neither anchors the raft to the seabed nor holds a fixed geographical position: currents can continue to carry a stabilised raft.
Marine, aviation and military designs
Marine rafts are stowed in arrangements including rigid deck containers and portable valises. A throw-overboard raft is launched into the water and inflated there. A purpose-built davit raft can be inflated, boarded at the embarkation station and lowered using the designated launching appliance. Self-righting designs turn back from an inverted position; others require a person to use their specified righting arrangement. Reversible designs can be used either way up.
Aircraft weight, stowage space and escape routes constrain raft design. Personal single-person rafts and larger crew or passenger rafts exist. Personal models can be stowed near the seat or attached to the wearer; inflation controls, retaining lines and connections to personal equipment vary accordingly. Even within one military single-person raft family, variants have inflatable or simple floors, different canopies or no canopy. A deck-raft deployment sequence therefore cannot serve as a procedure following an aircraft accident.
A civilian SOLAS design follows its particular maritime approval model. Military rafts may meet different requirements for dimensions, attachment and visible profile. Dark canopy, tube and lifeline materials, together with a switchable external light, reduce visual conspicuity in some designs. They also make visual location by friendly forces harder. Colour alone establishes neither load capacity nor concealment from every observation system.
Deployment and boarding
Before use, the available model's stowage location, accessibility, approved number of occupants, inflation control and deployment route need to be established. On a deck installation, inspect the container, cradle, lashing, capacity and servicing labels, and any fitted hydrostatic release unit externally. Cracks or separated container halves endanger the protection of the packed contents. Loose straps allow the container to move in its cradle; damaged straps threaten its retention. Check the hydrostatic release unit for cracks, deformation and a readable expiry marking that has not been exceeded. If a damaged or over-age release fails to free the raft automatically, the raft can go down with the ship. The deployment area must be clear; additional securing arrangements must not block the intended release. Opening a sealed container for a personal function check or firing the inflation system as a trial consumes or alters the system packed ready for use.
On a manually deployed throw-overboard raft, first secure the designated painter to its specified attachment point. It maintains the connection to the ship. The securing arrangement is released and the container deployed onto clear water according to the model's instructions. The specified pull on the paid-out painter operates the gas system. The raft must achieve its load-bearing shape before being loaded. Direct boarding from the vessel avoids additional cold-water exposure where the situation and facilities permit it. Jumping onto the canopy endangers its material and anyone beneath it.
A float-free installation follows a different chain. As the ship sinks, increasing water pressure operates the hydrostatic release, which frees the lashing. The buoyant container rises, pulls out the painter and uses it to trigger inflation. A purpose-designed weak link then separates the connection to the sinking ship. The securing arrangement, line routing and weak link must be compatible. A trapped container or an additional fixed connection can prevent it floating free. Contact with water alone deploys neither an arbitrary valise nor every aviation raft.
In the water, a light raft can drift faster than a person weakened by cold can swim. Its designated handholds and boarding ramp therefore matter as soon as it is within reach. An inverted raft requires its specified righting arrangement where applicable; an arbitrary lifeline does not provide the same leverage. Use the available foot and handholds when boarding. A connection to the ship initially keeps the raft at the embarkation point for people who can reach it. It must be released using the designated means before the sinking hull pulls it under. Once aboard, avoid the hull, wreckage and other obstructions. Paddles, if carried, assist with these short clearance manoeuvres; they do not make the raft a reliably steerable craft for a long sea passage.
Keeping the liferaft and its equipment usable
After boarding, first account for the raft's attitude, the people and the equipment within reach. Remove water with an available bailer, inspect load-bearing chambers, floor and canopy for damage, and secure objects against loss. When several occupants change position, consider weight distribution; huddling for warmth must not load one side disproportionately. Once no further people can reach an entrance, closing its designated cover reduces further ingress of water and wind. Maintain the intended ventilation.
Topping-up valves, pressure-relief valves and the inflation control have different jobs. Relief valves discharge excess gas; their normal operation must not be stopped by arbitrarily plugging them as if they were leaks. Available bellows connect to the designated topping-up valve of the affected chamber. A hole lets newly added gas escape again. Suitable leak stoppers or repair materials can then limit the leak where the damage and carried instructions allow. A failed tube requires reassessment of the load-bearing shape and water ingress even when other chambers remain inflated.
Use a fitted drogue according to its intended deployment sequence. Its drag helps reduce rapid wind drift and unstable movement, but also resists paddling clear of obstructions. Consider clearance from a hazardous hull or burning area and the intended deployment sequence. Wind, waves and current continue to determine the raft's displacement thereafter. Without ongoing position fixes, the accident position does not show where the raft will be later.
Cold conditions require protection from a wet seating surface, wind and further soaking; available floor insulation and protective clothing complement each other. In strong sun, the canopy reduces direct exposure while ventilation limits excessive heat inside. Drinking water, rations and a rainwater collector depend on the actual equipment pack and model. A collector provides additional water only when suitable rainfall occurs. Cold or heat, the occupants' condition, the available drinking-water supply and the continued functioning of the raft limit their remaining ability to act.
Detection, alerting and recovery
High-visibility colour, reflective tape and an external light, if fitted, assist visual search in different ways: colour provides contrast, reflective material returns incident light, and the lamp emits its own light. A radar reflector, if carried, improves the reflected radar signal. A radar SART actively responds to suitable search radar; an AIS-SART sends locating messages to receiving AIS installations within range. These functions assist detection. An available, activated 406 MHz distress beacon can instead report an emergency through the satellite system.
The devices available require their respective operating arrangements. A suitably designed EPIRB can operate in its intended floating position, tethered to something that will not sink. A PLB must operate above water with the appropriate antenna orientation; the body and equipment must not cover the antenna. If a beacon remains at the wreck or drifts separately, locating it leads to the device. Keeping available locating equipment with the occupants connects the transmitter's location to the raft. Device signals replace neither two-way voice communication nor observation by a crew.
In the British Maritime SERE training model, underwater escape training was combined with survival in personal rafts and subsequent simulated winch recovery. Within that sequence, the raft addresses the surface problem after escape; HUET addresses the preceding underwater escape. During a real isolation event, available forces must first obtain a usable location and be able to reach it. Military recovery also requires personnel authentication and tactical feasibility. Light and radio transmissions can reveal the location to an adversary. The actual signalling equipment and mission-specific communications instructions therefore determine its use.