Survival craft. Free-fall principle. Rescue boats. Liferafts

SURVIVAL CRAFT.

The survival craft are used in case the ship has to be abandoned in emergency situation to protect survivors from wind , rain, sea, cold, sun or extreme heat as well as to preserve survival with ration & survival aids. Survival craft include lifeboats & liferafts.  LIFEBOATS:                                                                                                         There are wooden, steel, aluminum & Glass-fibre Reinforced Plastic lifeboats. GPR lifeboats have a high corrosion resistance & a low maintenance requirements. That’s why almost all lifeboats nowadays are of GPR.

There are different types of lifeboats : open, semi-enclosed, totally-enclosed, totally-enclosed with a self-contained air support system & fire-protected.

• For passenger ships the capacity of the lifeboats is generally sufficient or every person on board.
• For cargo ships the capacity of the lifeboats is generally twice the number of persons on board.

All ships of 85m or more in length are required to have totally-enclosed lifeboats on board. Such boats have already been introduced for tankers. They provide better protection against the cold & the sea than the open lifeboats as well as they have extra top buoyancy so they are self-righting provided all openings are closed watertight & the persons on board are belted into their seats. If, however, such boat capsizes with the access or ventilation openings open it will adopt an attitude which makes it still possible to leave it above the water due to buoyancy chambers in the canopy. In less extreme situation it is often also possible to right the boat again.

Some models are sprinkled to provide a mist of sea water around it if sailing through burning oil It should be able to resist the flames up to 8min.Such models are equipped with internal air supply.

Semi-enclosed lifeboats are most often used on passenger ships so long as in emergency situation these can be occupied by more persons more quickly.

Lifeboats are launched either by davits or free-fall method. Semi-enclosed lifeboats are not suitable for free-fall launching  & are always launched from davits.

The free-fall boat is a special totally-enclosed lifeboat launched by free-fall principle .To minimize shock & stress impact on passengers during the fall from up to 40m the boats are designed with rearfacing seats & safety belts. Such boats are self-righting.

Free-fall principle.

Free-fall launching appliance has the boat stowed at the upper end of a launch way mounted over the stern, bows facing outboard. Fully manned it can from there:

• Run down the rollers of the launch way once the unlocking arrangement has been trigged & then enter the water in free-fall from the stern;
• Be lowered into the water with the aid of the launching appliance;
• Float free when the vessel sinks.

The unlocking arrangement is trigged from inside the boat by manually operated mechanical or by hydraulic device.

As for the davits there are several their types such as gravity-type davit, radial davit & luffing davit. The gravity-type davits are divided into single pivot davit & roller track davit.

RESCUE BOATS.

Rescue boats are separate type of LSA. They have two principal purposes, namely:

• The rapid rescue of persons floating in the water;
• Gathering , keeping in position & towing of liferafts.

They are built & equipped with these purposes in mind.

Rescue boats may be of rigid or inflatable construction or of a combination of both. Their length must be not less than 3,8m & not more than 8,5m. They must be capable of holding at least 5 persons seating & 1 person lying down. RB must have either an adequate high of board or a bow canopy extending over at least 15% of the length. RB have either an inboard or an outboard motor which enables them to achieve a speed of at least 6kn running free & 2kn towing. Rigid RB are subject to substantially the same construction regulations as lifeboats. As for inflatable RB there are different special regulations:

• They can be launched & recovered  with a full crew & fully equipped;
• Stowed on the open deck without protection they must be capable to withstand all weather condition on the open sea or to stay afloat for 30 days on the open sea;
• Shall have 5 roughly equal compartments. A positive free board must be retained even one compartment is damaged. The RB is designed to be launched from the ship within a few minutes. It is equipped with davit hooks with automatic release after the boat is waterborne. This facilitates launching when the ship is underway. The RB must at all times be ready for use.

LIFERAFTS.

If it is not possible to launch the lifeboat it may be necessary to use the liferafts to abandon the ship. There are rigid & inflatable liferafts , the former, however, are very seldom used nowadays. Inflatable liferafts are automatically inflatable. The rafts may be inflated on board & launched by davit or they may be thrown overboard in their container & then be inflated.                                            

Inflatable liferafts are made in different sizes:  there are liferafts for 6,8,10,12,15,16,20,25,or 50 persons, throw overboard type; for 35 persons davit launch type & large liferafts for 30,35,60 or even 65 persons without any protective canopy. Such type is mainly used on passenger vessels in short international voyages. All liferafts are so installed that they can be launched quickly, securely , safely & if possible by one man even with 20’ list over, the high side. For that reason liferafts are nowadays almost always stowed on swinging-out storage frames, inclined ramps or equivalent appliances.

Every inflatable liferaft is made from coated synthetic fabric & as a rule is packed tightly folded in a plastic container. On passenger vessels liferaft may be packed in a waterproof carrier bag. The weight of a liferaft including its packing & full distress gear lies between 100 & 185kg, depending on the size of the raft.

Every inflatable liferaft must comply with the following requirements:

• Liferaft must be capable to withstand all weather condition at open sea for 30 days
• It is operable over an air temperature range from –30’C to +66’C;
• It is stowed in a buoyant container;
• It can be thrown into the water in its container without the raft or its gear suffering any damage;
• It has adequate stability in seaway;
• It must be divided into compartments so that the raft can stay afloat even if only half the compartments are inflated;
• The floor is waterproof & can be inflated for insulation against cold;
• The liferafts must be equipped in accordance with the SOLAS requirements.

For inflation & to connect the inflated liferaft to the ship there is a release painter line which is cut using a knife. CO2 using for inflation is activated by hauling on release painter line. All approved liferafts must be equipped with an automatic release gear (Hydrostatic Release Gear) which makes the raft release automatically under water if no time is left for manual release. They will float to the surface if the ship sinks.  In the event of capsizing the raft can easily be righting by one person. Liferaft has also a fitting for securing a towrope. As for the davit launching it advantage is that the evacuation may be “dryshod” so long as the embarkation takes place from deck before the raft is launched. Lowering of the raft is effected by pull in a break wire & hook release is automatic when the raft is waterborne.