200062 Lifeboat Lowers Itself

Lifeboat Lowers Itself
Report No. 200062

During an officer training exercise the portside lifeboat descended uncontrollably down to sea level. We were very fortunate that the training had been postponed from the previous day when the ship was at sea and not at anchor and we were extremely fortunate that at that stage of the training no crew were inside the boat. Subsequent investigation showed that the wire rope falls had been renewed with wire rope from an American supplier. The correct type of wire had been supplied but due to the Imperial system of measurement continuing to exist within the U.S.A., the requested wire diameter of 16 millimetres had been substituted for ¾ inch. The diameter of the new wire rope falls had now increased from 16 to 19 millimetres with consequences unforeseen by ship's staff.

Training was to be given on the correct method of lowering the boat both from outside and inside the boat and all officers, deck and engine, were assembled at the port lifeboat. For this purpose the boat was prepared in the normal manner and subsequently lowered to the boat deck. After the first practice, the boat was raised up and again lowered by the same officer. This time, the boat continued down out of control and did not stop until waterborne. During the boat descent it was clear that the remote control wire for releasing the winch brake was under strong tension and that this was the cause preventing the brake being applied and stopping the boat.

These boats are designed to be boarded and then launched from the stowed position only. The design is such that the winch brake is to be operated only by remote control for any real emergency - abandon ship. The brake remote control is a wire connected between the boat operator and the winch brake handle. By simply pulling this wire up and down the winch brake can be released or applied as required. So, what went wrong? In order for the operator to get a physical grip on the wire a steel triangle handle is clamped on to the control wire inside the boat approximately 20 to 30 centimetres from the deckhead. After investigation, it was found that the actual effective length of the control wire was reducing in proportion with the distance the boat was lowered. Therefore, as the control wire became shorter, at some point the triangle handle came into contact with the boat deckhead. From that point onwards the effect of the reducing length of the control wire was to place tension on to the winch brake handle and release the brake. The more the boat descended, the more the brake was released. The boat lowered itself.

It is logical to expect the design of the system will ensure that the brake control wire will lower out at exactly the same rate as the boat is lowered. From past experience this is not the case but any differences between the lowering rate of the boat and the lowering rate of the control wire have been fairly small, although not always insignificant. The length differences above prevent us from using the remote control brake effectively and safely and the boat cannot be lowered from the inside position in a proper manner.