What’s to Know About Life Rafts

About Life Rafts

 

Re-printed from Mariners Diary – ‘The handiest boating book’

Life rafts come in many shapes and sizes with virtually no standardisation between manufacturers. Square, oval, hexagonal, octagonal, single buoyancy tube, two stacked tubes are just some of the choices. Cost, weight, intended purpose and people-carrying capacity are usually the determining factors. All life raft manufacturers try to satisfy the mutually exclusive aims of making their rafts and equipment the simplest and most foolproof possible while providing the most features. No-one ever expects to have to use their raft but it remains a salutary thought: your life and that of your crew may one day depend on it, so choose your life raft carefully.

 

Construction/build quality: Most life raft air tubes are made from either PVC, nylon reinforced butyl rubber or polyurethane. Some also have an outer cover of welded PVC that protects a PVC bladder. Quality rafts, including those to SOLAS (international shipping) standard, tend to be made from polyurethane, while cheaper versions are usually constructed of welded PVC. Whichever fabric the raft is made of, initially it needs to withstand being squashed into a tight container for an extended period. On launching, it must withstand rapid inflation from a gas that enters it at freezing temperatures. The International Organisation for Standardisation (ISO) has established a range of criteriadetailing all the materials used in the construction of life rafts and their performance requirements including; inflation, launching, material resistance, buoyancy and interior space. All SOLAS rafts must be certified and stamped to show that they meet these demanding construction and performance standards and for rafts found on coastal shipping and recreational vessels, the recently introduced ISO 9650 certified standard is highly recommended.

 

Buoyancy Tubes: Where single tubed life rafts were once found on coastal and blue water vessels, they are no longer used except for aircraft and some search-and-rescue applications. Two stacked buoyancy tube rafts are now mandatory because they provide a redundancy safety margin. Either of the two tubes is designed to support the raft’s maximum load on its own. Unlike a car tyre or even an inflatable boat, the tubes of a fully-inflated raft are maintained at a relatively low pressure of only about 2 psi. It’s the volume of air, not its pressure that supports the weight - so any leaks that may develop are reasonably easy to deal with, by either applying repair patches or inserting leak stoppers into any holes. 

Life raft

 

Shape: With a space allowance of only about 1.2 square metres per person, no-one can expect a life raft to be luxurious, but its shape can effect comfort and morale. The choice however, finally depends on certain trade-offs. For example, a rectangular or square floor may mean that several adults can stretch out and lie down. The raft’s centre of gravity is lowered which increases stability. But a round shape provides greater strength uniformly around its perimeter compared to a rectangular floor, but may only allow one or two persons to stretch out flat in the centre. Survivors sitting in a round raft will automatically tend to position themselves around the sides, with their backs against the tubes and feet inwards. Their weight will be distributed evenly.

 

Floor & Canopy: As well as protection from wind and sun, a raft’s other role is to keep you warm and dry. A single membrane floor and roof could allow rapid heat loss. This may become life-threatening very quickly, particularly in colder temperatures and higher latitudes. SOLAS life raft standards require an insulated roof and floor, but this can result in a bigger, heavier and more costly raft. Insulated floor choices available are: a sandwich of layers with a core of cellular foam, a fabric base with an aluminium film on top to reflect body heat, or an inflatable floor that needs to be independently pumped up after the raft is boarded. Insulated canopies usually have a double-skinned membrane that is self-erecting.

Insulated floor

Composite foam insulated floor

 

Inflated floor

Inflatable floor

 

Weight and Manageability: Even a basic four-man raft is quite heavy while a so-called light-weight raft, primarily designed for weight conscious racing sailboats, could be half the weight of a standard version. Light-weights are often made by what is called bent tube construction, where a single continuous top and bottom tube is simply bent at each corner and welded. The floor is highly critical to the design to maintain overall shape and integrity. Light-weight rafts are a popular choice with coastal sailors, in that they are light and easy to manhandle and relatively inexpensive, but unfortunately it was such a raft that failed in the 1998 Sydney to Hobart disaster when its floor was cut. Regulations and demand for more features has seen significant changes to life raft design since then. Nevertheless in an extreme emergency and particularly when conditions are rough, getting a raft over the side can be a difficult task. Having a prearranged method in place where even the smallest crew member can remove a standard raft from its locker or storage place and prepare it for deployment is certainly good practice.

raft being man-handled onto boat

 

Access: Nearly all rafts larger than eight person have openings on opposite sides. Gaining access to a single opening raft in extreme conditions can be difficult, when stepping down from a boat while trying to rotate the raft. A double entry system is mandatory for larger commercial life rafts and standard on larger recreational versions, but the down-side is that it may lessen security and allow more water ingress.


Very often, rafts need to be accessed from the water and this can be difficult. Assistance is normally provided by a weighted multi-rung ladder and/or a semi rigid boarding ramp plus a webbing handhold to haul yourself over the buoyancy tubes. The coroner’s finding into the 1998 Sydney Hobart disaster stated that sailors who were cold, fatigued and weighted down with foul weather clothing and inflated lifejackets found it extremely difficult to board a life raft using a simple webbing ladder. To aid entering a raft, it is now accepted that single entry rafts and the second entry point on larger rafts should be fitted with a hard or semi-rigid boarding ramp. The Coroner was also highly critical of the methods of securing the opening of some raft types. Access flaps secured using fabric ties were impossible to undo and retie and are now discouraged in raft manufacture.

person in entrance of raft

 

Stability: Life raft stability is influenced by a number of factors: raft shape, wind getting under the floor, canopy shape, loading of occupants, sea anchors and water ballast. But it is the combined force of wind and waves that cause rafts to capsize and water ballasted stability bags, firmly attached to the raft’s underside, help to resist this occurrence. They should be triangular in section and fill with water within seconds of inflation to increase stability and reduce the risk of capsize. SOLAS and ISO 9650 standards require that stability bags be weighted and each capable of containing at least 22 litres of water. The important role of the sea anchor or drogue should also not be overlooked. Numerous authoritative tests have shown that they deliver a powerful stabilising force that help prevent capsize. To be effective, they should be a tapered sleeve of heavy duty fabric, about twice as long as the mouth is wide.

Stability

In calm conditions, wind presses down on the canopy and helps to keep the raft level. In rough weather, rotational forces come into play whereby a breaking wave in combination with the wind on the canopy can cause the raft to lift, allowing more wind under the floor. If the occupants are thrown to the low side, the raft is likely to capsize.

 

Observation/ventilation port: Most people will be seasick if they are in a raft for any length of time. Raising the canopy in rough conditions for this or other reasons could allow much water ingress without this important feature. They also allow a watch for possible rescue activity.

 

Lights: Most rafts have two lights fitted, one white or orange-coloured light outside on the roof centreline and one white-coloured light inside. The outside light is not primarily designed for search and rescue purposes; its purpose is to aid spotting the raft from the disabled boat at night. Lights can be powered by either a special water-activated battery that can’t be turned off, or a lithium type that can be de-energised by a switch or by removing the batteries. In both cases the power cell will power the globe(s) for up to 22 hours. (SOLAS requires a minimum of eight hours). 

lights

 

Rainwater catchment system: This is usually a fabric vee gutter stitched into the canopy that leads to a closable delivery pipe within the raft. It’s a simple but reliable system that allows replenishing of the most precious commodity on board, water for drinking and for washing injuries and salt-water induced sores.

rain water catcher

 

Rescue support: Simple components such as a radar reflector and retro-reflective tape segments aid rescuers locating life rafts. Radar reflectors can be incorporated into the raft canopy as a metallised reflector panel or as a separate passive component that is unfolded and deployed on a pole above the raft canopy. SOLAS requirements and rafts built to ISO 9650 standards require both a radar reflector device and retro-reflective tape segments. The highly reflective tape-segments (a hexagonal-pattern that bounces light back toward a light source) aid visual sighting by maximising a ship or aircraft’s spotlight. They must conform to strict manufacturing standards and occupy a minimum surface area of the raft’s top and underside. In his findings into the 1998 Sydney to Hobart Race disaster, the Coroner suggested stability bags and raft bottoms be made in a highly-visible colour. Perhaps surprisingly, up to that time, many life raft bottoms and stability bags were black coloured and the Coroner found that the sighting of dark coloured upturned rafts by searching air and water craft to be extremely difficult. Quality life rafts now incorporate highly visible stability bags and floor bottoms into their raft design.

rescue support – retro

 

Stowage: Life rafts can either be stowed in a non-waterproof soft valise for underdeck or locker storage or on deck in a hard fibreglass or plastic canister. The valise option still requires that the raft be protected from chafing and sharp objects and a dedicated locker devoted to abandon ship equipment is highly desirable. Otherwise the raft will get buried beneath sails or other regularly used gear. The valise pack also means that there is no way to fasten the painter/activation lanyard to the boat while the raft is stowed. But hauling a raft topside, or retrieving it from a poorly accessed locker, under the most difficult of conditions is certainly a reason why a deck mounted canister stowed raft is a good choice. Yachting Australia now requires that yachts competing in its races have all rafts stowed on deck, preferably accessed from specially-assigned deck lockers. 

stowage can

 

 

What to expect on deployment of your life raft

people in water near raft

 

people in water near raft

 

Inflatable life rafts are usually deployed by one of two methods: The first and most common launching method is by manually throwing or dropping the raft overboard. These rafts are often referred to as ‘throwover type’ even though they can also be automatically deployed by a Hydrostatic Release Unit (HRU) if the vessel in distress rapidly sinks. 

In the second deployment method, an inflated raft is lowered into the sea by means of a davit launching mechanism, called the ‘davit launch type’. This type is the domain of big capacity rafts and is usually a feature of large high-sided ships. 

On smaller vessels an inflatable life raft is usually launched by throwing the entire container or valise overboard and pulling its lanyard. A surprising amount of line (at least 8 metres) will need to be pulled out before this action activates a compressed gas cylinder which inflates the various air chambers that make up the raft. The raft will inflate quickly and depending on the pack type, easily cause the two halves of its container to separate, or burst out of its valise carry case. The compressed gas cylinder is over-pressurised and excess gas will gush out of the relief safety valves after the raft has reached its correct operational pressure. At much the same time, the ballast bags attached to the hull of the life raft will fill with sea water and significantly stabilise its movement. 

The sea anchor (drogue) will stream automatically on deployment in some raft types and in others it will need to be manually set on boarding (it lays folded on the floor). The drogue will hold the raft up to the wind and waves and significantly reduce the chance of capsize. It should also tend to keep the raft’s opening to the lee of the weather. 

A raft is designed to inflate the right way up (by way of prudent design and because of the weight of the compressed gas cylinder and emergency equipment pack lashed to the raft’s floor) but there is a small chance that it may inflate upside down. Extreme weather can also play a significant role. If the raft becomes inverted, righting from the boat is always preferable, but if that fails, it will need to be done from the water. The diagram below shows the suggested technique. 

Many people find it surprisingly difficult to get over the high freeboard of the tubes even with the aid of an entrance platform or ladder and webbing bridle. The most able person should board first and assist other crew members as required. A rescue quoit and line is immediately available at the raft’s entrance and should be thrown as an aid to persons some distance from the raft. 

Once aboard, it will be necessary for survivors to cut the lanyard and paddle clear of the boat in distress. Checking to see that the sea anchor is streaming correctly, tending injured victims and closing the door of the raft once all survivors are aboard are also priority actions. 

Maintaining the raft, familiarising everyone with the contents of the emergency pack, watching for rescuers and achieving best possible comfort levels for all on board will become the ongoing routine.

righting a raft

Righting a Raft

 

If a life raft inflates upside-down or capsizes, the gas bottle on a raft’s bottom can be used to right it. Turn the raft until the bottle is downwind, then climb onto the inverted raft. With the wind providing assistance, haul on the righting strap (usually on the side opposite the gas bottle), using the gas bottle to provide leverage

 

Deploying and Using your Life Raft in an Emergency Situation

 What to expect on deployment of your life raft

Preparations before Leaving Your Boat

1.     Put on as much warm clothing as possible, making sure to cover head, neck, hands and feet. If an immersion suit is available, put it on over warm clothing. Put on a lifejacket (PFD) and secure it properly.

2.     Send a mayday and activate EPIRB (if not already done).

3.      Ready the Emergency Bag / Abandon Ship Kit including additional water and blankets. Any available EPIRB and portable two-way VHF radio should be taken aboard the raft.

4.     Consider taking seasick tablets as most people suffer some motion sickness on boarding their raft.

5.     When ready to board, remove shoes and sheath sharp objects.

6.     Don’t launch the raft too early; in rough weather it will be difficult to hold alongside for long.

Priority Actions

1. Throw entire container or valise case overboard & pull painter to start inflation

Ready the life raft for deployment by removing the lashing on the slip hook that secures the container to its storage cradle. A valise packed raft should be brought to the launching area. Pull out a length of painter line from the container or valise and check that the painter’s end is firmly attached to a strongpoint on the vessel. If necessary, reposition the container and then throw or drop the entire container or valise overboard. Pull on the painter line until the remaining line is extracted from the container (this line is at least eight metres long). A final sharp tug will trigger the automatic inflation of the life raft.

2. Board life raft

Transfer any additional gear and survival supplies from the stricken vessel to the life raft. If possible try to stay dry. Crew members should board the life raft by ladder or rope from the mother vessel or by jumping into the entrance if height is not excessive. From the water, try to board the life raft as soon as possible in order to shorten the immersion time and subsequent body heat loss. Remember, cold is the greatest killer in maritime emergencies. Enter the life raft with the aid of the boarding ramp or ladder. Crew members should pull themselves up and slide into the raft head first. The internal lifelines and entry bridle may help survivors pull themselves all the way in. If required, throw rescue-quoit and attached line to other survivors in the water and haul them to the life raft. Disabled or unconscious survivors should be lifted under their armpits and slid backwards into the life raft.

3. Ready life raft to be freed from mother vessel

Check the life raft is functional and that both buoyancy tubes and arch are correctly inflated. If the mother vessel is still afloat, remain secured to it unless fire, imminent sinking or some other danger means it is advisable to sever the painter line. A disabled but floating vessel will always provide a greater search target for rescuers than will a life raft. If the decision is made to cut the painter, use the safety knife stowed in the pocket next to the raft’s entry. Try to save as much line as possible. Get away from the stricken vessel by using the paddles provided within the equipment pack. Tie multiple life rafts together as there is safety in numbers including more survival gear and expertise to share and it is easier to spot two rafts than one.

4. Deploy drogue (sea anchor) and close entrances

Check that the drogue has deployed automatically. Its primary role is to help the raft resist capsize but life rafts can drift rapidly and the drogue reduces the rate of drift and assists searchers by reducing the raft’s distance from the distress position. In hostile weather close entrances when everybody is inside.

5. Tend injured crewmembers

Keep victims as warm and dry as possible and, if necessary, refer to the first aid instructions provided within the emergency pack.

Subsequent Actions

1. Bail out water inside the life raft

A bailer and sponges are provided to assist in drying the raft’s interior.


2. Adjust ventilation

Ensure good ventilation at all times and adjust entrances and ventilator(s) to suit current conditions. By varying the point of attachment, the drogue can be used to alter the position of the raft’s openings relative to the seas, allowing more shelter or better ventilation.

 

3. Open emergency pack

Familiarise every crewmember with the contents and function of items within the emergency pack. When not required, lash down all gear so nothing is lost if the raft capsizes or is swamped.

4. Activate EPIRB

Confirm EPIRB is working and leave it on; don’t switch it off until advised to do so by rescuers.

 

5. Establish a watch system

One hour watches in pairs is recommended, one person should be on duty as outside lookout and the other on duty inside, responsible for the raft, water catchment etc.

 

Aids to Survival

1. Nominate someone to take charge.

 Good leadership and high morale are crucial for survival. A good leader takes on the responsibility of keeping the other survivors as organised, calm and comfortable as possible.


2. Take seasickness tablets as soon as possible

Even hardened sailors are almost certainly going to be seasick in a life raft. Seasickness interferes with your chances of survival by loss of precious body fluid, incapacitation and greater vulnerability to hypothermia.

 

3. Establish a routine

The discipline of a routine focuses attention on the positive work of survival and ensures that essential tasks are done. Suggested routine:

       Watch for ships, aircraft, survivors and useful wreckage.

       Flash the signalling mirror all around the horizon when there is sunshine – rescuers can see your flashes before you can see them.

       Look for signs of land.

       Maintain the life raft – tube inflation, a dry floor, adequate ventilation, equipment, etc.

       Track rations consumption.

4. Water Use

Other than injured persons, survivors should drink no water on the first day. This causes the body to activate water saving mechanisms. Thereafter allow ½ litre per person per day, using the marked measure to ration. Drink water in sips throughout the day to minimise urination.

Collect rain water when possible and use this before the sachets. Maintaining your body’s water balance is a prime requirement of survival as water is the major constituent of our bodies. Water is a higher priority than food. You can probably live for weeks without food, but your survival will be measured in days if you have no water. Food digestion drains needed water from your body and exaggerates thirst, so if water is in short supply, don’t eat. Drinking saltwater will promote water loss through the kidneys and intestines and shorten your survival time. A rainwater collector is incorporated into the canopy and a flexible tube on the inside allows rainwater to be collected in plastic bags or empty containers.

 

5. Avoid exposure to strong sunlight

6. Arrange suitable sanitary arrangements

Attempt to keep life raft interior clean.

 

Maintaining the Life raft

1. Buoyancy Tube Pressure

If necessary increase the pressure in the buoyancy tubes using the hand bellows and connecting tube provided in the equipment bag. Top-up valves are fitted to both tubes just inside the entrance and on the arch. Note: Pressure relief valves fitted on the outside of the raft may operate and emit a whistling sound when releasing excess gas pressure.

 

2. Life Raft Repairs

If a leak is discovered in a buoyancy tube, immediately repair it by sticking on a patch from the repair kit, or by screwing in one of the conical leak plugs, or by applying a repair clamp. Carefully top up with the bellows after repairing. If one buoyancy tube is deflated, the other tube will keep the survivors afloat. 

 

3. Overturned Life Raft

Although unlikely, in rough or windy conditions your life raft may overturn. One person can right a capsized raft if it is done quickly, before the canopy fills with water. To right the raft, swim to the side marked RIGHT HERE – this is the location of the heavy inflation cylinder. Turn the life raft canopy into the wind and reach up and pull on the righting strap using the cylinder pocket as a foot support. As the raft turns over, swim clear quickly. If the inverted canopy is full of water, the raft may be more difficult to right and more people may be required to pull on the righting strap. 

 

 

4. Canopy Light

During daylight hours, conserve the canopy light’s battery by either inserting the activation pin that is attached to the lithium battery pack, or with LED canopy lights, press the battery pack’s on/off buttons - separate switches control the interior and exterior light.

 

Pyrotechnic Signals

There are only a limited number of pyrotechnic signals available within the emergency pack and these should only be used when there is a strong likelihood that they will be seen.

Hold flares away from the life raft, on the downwind side if possible.

Read pyrotechnic instructions fully before use. 

Parachute Signals: Use when there is good reason to believe that inhabited land, a possible rescue ship or aircraft is within the estimated visibility range of your signals.

Hand Flares: Use when the light of a ship, or aircraft, or lights onshore are visible to you. Red hand flares can also be used in daytime.

Smoke Signal: Use in daytime when a ship, or aircraft, or inhabited land is visible to you.

 

How Do Hydrostatic Release Units (HRU) Work?

How do hydrostatic release units (HRUs) work

Most HRUs operate by water pressure alone depressing an internal diaphragm to operate the release mechanism or water ingress into the unit activates a sharp blade which cuts the strong rope that secures the raft to its cradle or mounting position. With either type, upon immersion and at a depth of 1.5 to 4 metres, the raft will float free and inflate as the painter line is fully extracted from its container. A weak linkage finally frees the life raft’s painter line from the vessel as it continues to sink and the life raft floats free.

 

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