Inflatable Life Raft

1. Buildings on top of life rafts affect hydrostatic pressure release

In addition to the additional life rafts equipped with SOLAS Ch/Reg31.1.4, the life rafts should be stored with hydrostatic pressure releases connected to realize the free-floating function. Figure 1 shows the life raft arrangement of a car ferry, where the life rafts are stored between the two decks, which prevents free-floating. There are two ways to rectify the situation: to change the storage position of the life raft, or to assess the spacing between the upper and lower two decks of the life raft to add a sliding guide bar. It is a common way for many passenger ships and container ships to choose a guide bar to meet the free-floating function when the life rafts can't avoid the upper deck due to the ship's structural problems.

Figure 1 Liferaft arrangement of a car ferry

2. Restrictions on the storage height of life rafts

LSA Regulation 4.1.1.2 requires that a life raft shall be constructed in such a manner that the life raft and its appurtenances will be satisfactory for use after being dropped from a height of 18 m. The life raft and its appurtenances shall be tested at a height of at least 18 m above the waterline of the lightest navigational craft. Where a life raft is required to be stored at a height in excess of 18m above the waterline of the lightest navigational load, it shall be subjected to a satisfactory drop test from at least that height. Usually, the life raft storage height is at least 18m, however, for some large ships such as Capesize bulk carriers, life rafts are usually arranged in the main deck higher than the life deck (generally used for storing rescue boats and life rafts, lifeboats are mounted on the stern of the free landing type), from here to the lightest load of the navigation waterline is about 20m, the height of more than the ordinary maximum storage height of the life rafts, this time, should be noted that The maximum storage height specified in the type approval certificate of the life raft, Figure 2 shows the storage height of different models of life rafts of a manufacturer.

Figure 2 Maximum storage height for type approval certificates

In accordance with SOLAS Ch/Reg 31.1.4, cargo ships with a horizontal distance of more than 100m from the foremost point of the bow or the end of the stern to the nearest end of the nearest lifeboat raft shall also be provided with one life raft as far as reasonably practicable, stowed as far forward or aft as practicable. Ships generally use life rafts with a rated capacity of 6 persons, and ships should avoid using 6- or 8-person life rafts recognized in accordance with the regulations for fishing vessels, which are generally recognized as having a maximum stowage height of only 8m.

3、Choose the right life raft raft frame

There are two kinds of common rafts, flat rafts and slanting rafts. Flat rafts generally need to lift the life raft to launch rafts, characterized by easy installation, rafts and storage cylinder contact surface is large, the storage cylinder is not easy to deformation, the disadvantage is that it is not convenient to throw. Inclined raft frame type more, commonly used throw type, cascade type and row throw type, etc., characterized by the use of as long as the release of the life raft binding rope, the life raft can be automatically slipped along the slope of the raft frame in the sea, the disadvantage is that the installation is inconvenient.

Usually, the life raft with weight ≤185Kg can be installed on the flat raft frame, and the life raft should be thrown into the sea by lifting up or launching out when used, and the heavy life raft ≥185Kg should be installed on the tilting type raft frame in principle. At present, the design and manufacture of rafts are mainly based on the People's Republic of China shipbuilding industry standard CB3068-91, "Gas Expansion Life Raft Rack" requirements. Note that the choice of raft frame is not only easy to use or industry recommended standards, but also one of the conditions of exempted life raft landing device.

4. Life raft hydrostatic pressure relief device connection

When the life raft is too late to be released manually, the life raft tube sinks with the sinking ship. When sinking to 2~4m from the water surface, the hydrostatic pressure release device will automatically release the tie rope of the storage cylinder due to water pressure, and the life raft cylinder will float out of the water surface freely. Then, as the ship continues to sink, with the help of the buoyancy of the storage cylinder itself, the first cable is continuously pulled out from the storage cylinder until the valve of the gas cylinder is opened, so that the life raft is inflated and formed, and when the ship continues to sink, the easy-to-break ropes are pulled out, and the life raft will be detached from the sinking ship and floats out of the water freely.

It is often found in daily work that the hydrostatic pressure releases, bowline cables and weak rings of life rafts on board are not connected in the correct way. Hydrostatic pressure releases can be in the form of two pressure diaphragms or spring cutters, the former are inspected once a year together with the life rafts and the latter are labeled with an expiration date, usually 2 years. The first cable of the life raft should be ensured to be connected to the weak ring, usually the first cable will have a cable to connect to open the gas cylinder, there are some manufacturers set up independent gas cylinder valve cable, independent cable does not need to be tied to the weak ring together with the first cable. Be sure to use one hydrostatic pressure release per life raft or life raft group.