n my opinion, a stable hook has the load point directly over the pivot center. The hydrostatic interlock and pin serve a valuable function in an unstable hook system, not in a stable hook due to a hook design that uses the weight of the boat to open the hook. It is therefore desirable to add additional safety features to prevent a premature release. Without these features it would be possible for an operator to operate the standard release handle and unintentionally release the lifeboat when suspended above the sea, with potentially catastrophic consequences.
When the lifeboat is suspended above the sea the whole weight of the boat is holding the hooks closed. It is not possible for an operator to operate the standard release handle and unintentionally release the lifeboat when suspended above the sea. In my opinion, the addition of a hydrostatic interlock and pin would therefore serve no purpose.
Hydrostatic interlocks require regular maintenance and if incorrectly maintained, can malfunction. Improperly maintained hydrostatic interlocks have been known NOT to engage correctly when the lifeboat is suspended above the sea. In such a case they cannot prevent a premature release. They have also been known to remain engaged when the boat is in the water and hamper the release of the hooks when the lifeboat reaches the sea.
Hook pins are only of value, if operators remember to manually insert the pins. In addition, if operators do not remember to manually remove the pin in an emergency, the lifeboat will not be able to release from its cable. For inherently unstable hook systems the ability of a hydrostatic interlock and pin to prevent the premature release of the hooks outweighs the negatives associated with these elements. Inherently stable hooks receive no benefit from hydrostatic interlocks or pins; however inclusion of these will impose the negatives associated with these elements.
* -Addition of hydrostatic interlocks or pins to unstable hooks is recommended. They add additional safety features to an inherently unstable design.
* - Addition of hydrostatic interlocks or pins to stable hooks can possibly not be recommended. They add no positive benefit, but in fact can have a negative impact, to inherently stable hooks and make the operating procedures even more cumbersome.
Unlike any other carriers; lifeboat releases are designed to ‘fail to unsafe’. E.g, if an elevator cable fails, the elevator stops. If a lifeboat hook fails, the boat falls.