(b) Lowering and Raising of Lifeboat with Safety Features
Lowering a Lifeboat
The lowering process relies on gravity. First, the gripes and safety pins are released. The winch's hand brake is lifted, allowing the lifeboat and its cradle to roll down the inclined trackways. The boat is lowered until it reaches the embarkation deck level, where passengers can board. The lowering is then continued, with the weight of the boat transferred to the wire falls, until it is safely in the water. The descent rate is controlled by two main safety features:
- Centrifugal Brake: This governs the maximum speed of descent to a safe limit, typically around 36 meters per minute. This feature works automatically, ensuring the boat doesn't free-fall.
- Deadman's Brake (Hand Brake): This is a manual brake that must be actively held in the 'off' position to allow lowering. If the operator loses control or releases the brake lever, it automatically re-engages, stopping the descent. This prevents uncontrolled lowering if the operator becomes incapacitated.
Raising a Lifeboat
To raise the lifeboat, the winch is engaged. A key safety feature during hoisting is a ratchet arrangement that prevents the drum from reversing and dropping the boat back down in case of a power failure. Additionally, an automatic cut-off switch is fitted in each davit arm. This switch senses when the cradle has reached its final stowed position and automatically cuts off the power to prevent over-hoisting and potential damage to the davit structure.
SOLAS Requirements for Hoisting
As per SOLAS 74 (International Convention for the Safety of Life at Sea), every lifeboat launching appliance must be capable of hoisting the boat, loaded with its full capacity of equipment, at a rate of not less than 0.3 meters per second (0.3 m/s). This requirement ensures that the lifeboat can be recovered efficiently after use or for maintenance.