The misuse of the Lifeboat davit brakes is the single most common error mariners make when launching lifeboats.
Lifeboat davits are equipped with two separate braking systems: a holding brake and a centrifugal brake.
Holding Brake
The holding brake is designed to stop and hold the lifeboat stationary at any point between its fully housed position in the davit or when it is near the water’s edge. The holding brake is disengaged by lifting the weighted brake handle thus allowing the lifeboat to descend downward toward the water.
A centrifugal brake is provided to control the rate at which the lifeboat is lowered. This limits the rate of descent of the boat when the hand brake is not engaged. Brake shoes of calculated weights act on the inner surface of a stationary drum, being thrown outward by centrifugal effect against the restraining springs. The lowering speed of the boat can be kept within the required 36 m/min
Centrifugal Brake
In many cases winch operators are unaware of how the centrifugal brake system works and end up controlling the rate of descent of the lifeboat entirely with the holding brake. This is very much like driving your car and accelerating with your foot on the brake at the same time. When abusing the brake system in this manner two things happen:
- The holding brake will wear out very quickly
- The centrifugal brake will be compromised and over time will not work as designed.
The best lifeboat davit braking procedure: All manufactures recommend that the holding brake be completely disengaged when lowering the lifeboat to the water. When the weighted handle is raised and the holding brake is disengaged the centrifugal brake will engage automatically when the winch drum exceeds a preset rotational speed, in the down direction, and smoothly lower the boat.
Lifeboat Winch
It is probably easy to understand that if you lower the boat with the holding brake disc partially engaged it will wear down the brake lining due to excessive friction, but it may not be obvious how this practice adversely affects the centrifugal brake. When the decedent of the lifeboat is controlled entirely by the holding brake the centrifugal brake never reaches the preset rotational speed necessary for engagement and the brake pads spin but do not come into contact with the drum. The centrifugal brake is centered on the winch shaft and enclosed within a weather resistant steel housing. When used as designed the centrifugal brake shoes rotate outward and come into contact with drum. This activity helps to keep:
- the surface of drum clean and prevents corrosion from forming
- the interior of the brake assembly dryer by heat created from use
- the brake shoes from forming slime
- the moving parts flexible.
Properly using your lifeboat davit’s braking system may not be intuitive because you cannot see the centrifugal brake. To do this as it should be then becomes a matter of training. Northwest Maritime Academy has constructed a purpose built full scale lifeboat davit system that permits the students the opportunity to practice this braking proficiency. NWMA believes that through proper training mariners will become a more confident member of the survival craft team.