Answer MEP Question 62

Q. With reference to lifeboats, Sketch and describe: 

A. The handbrake used for lowering and state how it may be tested. 

B. The centrifugal brake and method of testing. 

C. A roller ratchet and the method of testing; 

D. Why is ratchet incorporated into the systems. 

A. A handbrake used for lowering and state how it is tested; - Lifeboat davits vary in design to suit the load to be handled and the layout of a ship, but the principles are common to most davits. 

When lowering a lifeboat, no mechanical assistance apart from gravity is applied, the only manual function required of the operator is to release the winch handbrake and hold it at the off position during the lowering sequence. If the operator loses control of the brake lever in difficult conditions, the attached weight will provide a positive means of application and the boat will be held at any intermediate position. 

- This condition applies throughout the outboard movement of the boat, from its stowed position until it is waterborne. 

- The hand brake is fitted with two shoes, pivoted at one end and coupled at the other with the weighted lever, by a link. The lever projects from the casing through a watertight seal. 

- The shoes are Ferodo-lined and have a normal useful life of five years or more. 

Testing of Handbrake 

- The lifeboat is loaded to its optimum carrying capacity and the dead man handle is lifted to ensure lowering of the lifeboat and the handle is released to ensure the boat is held in that position without any further movement. 

B. The centrifugal brake and the method of testing. 

- centrifugal brake limits the rate of descent of the boat when the handbrake is not engaged. 

- Shoes of calculated weight act on the inner surface of a stationary drum, being thrown out by centrifugal effect against the restraining springs.

- The Lowering speed of the boat can be kept within the predesign limit of 36m/min.

- A ratchet arrangement ensures that the drum will not reverse and the boat drops back towards the water in the event of a power failure when a boat is being hoisted.

Testing: The centrifugal brake is also tested the same way as the hand brake, while the hand brake is disengaged the lowering speed is measured which shall not exceed 36m/min.

C. Roller ratchet and the method of testing:

The roller ratchet will lock the brake drum against lowering until the ventral can is rotated a small amount by lifting the handbrake lever. The static test on the handbrake will also test the roller ratchet.

D. Explain why the ratchet is incorporated into the system;

The roller ratchet is fitted alongside the hand brake and is required so that when the process of lifting the lifeboat back to the davits is interrupted (e.g. power failure) the fall will lock in that position and not start to lower.