The lifeboat is constructed of fire-resistant polyester resins and fiberglass. The hull, inner hull, canopy, and roof are all individually moulded in one piece. The area between the hull and inner hull will be filled with synthetic foam for buoyancy, which will keep the lifeboat floating and upright even if it is holed below the waterline. When filled with its full complement of people and equipment, the lifeboat has ample stability in a seaway and sufficient freeboard, and in the event of capsizing, it can automatically acquire a position that will allow the occupants to escape.
There are different ways of launching a life boat from the vessel in case of an emergency:
- Free fall
- Using a davit
We are not going to explain the launching procedure of these life boats, as same can be found in the SOLAS manual or poste on the vessel life boat’s launching sites.
As most of the vessels are equipped with the latter version, in this post we will explain about break system of the launching davits as they are very important and need to be properly adjusted as the safety of the crew and boat is highly dependable on the breaking system.
Lifeboat davits have two distinct braking systems: a hand brake (static brake) and a centrifugal brake.
The hand brake arrangement consist of a weighted lever, a brake drum with break shoes and break lining.
Its only function is to control the speed of descent. Lifting the lever using a remote line from the lifeboat or the boat deck. The winch can then lower the lifeboat using gravity. Releasing the hand brake, on the other hand, will halt the lowering procedure.
The lifeboat can be stopped and held in place by the manuakl brake at any time between its fully housed position in the davit and when it is close to the water’s edge. By pulling up on the handle attached to the weighted brake, the holding brake can be withdrawn, allowing the lifeboat to move closer and closer to the sea.
A centrifugal brake is located on the winch. The brake controls the speed of descent for the lifeboat. The centrifugal brake has a brake lining on top of the breaking shoe and restraining springs. When the boat is lowered, the centrifugal effect pushes brake shoes outwards against the restraining springs. Thus, the centrifugal break restricts the lowering speed of the boat to not more than 36 m/min. The brake is enclosed, and provides reliable operation in all climate conditions. Normally, the winch is fitted with a one-way clutch, so in the event of power loss during hoisting, the brake will automatically activate and davit motion will stop.
Because winch operators frequently lack an understanding of how the centrifugal brake system functions, the holding brake is frequently used to control the rate at which the lifeboat is lowered into the water. This is extremely similar to driving a car while simultaneously pressing on the accelerator pedal and the brake pedal at the same time. When the braking system is abused in this manner, two things occur:
- The retaining brake will experience very rapid deterioration.
- The centrifugal brake will be damaged, and after some time, it won’t function the way it was intended to.
When lowering the lifeboat into the sea, it is imperative that the holding brake be entirely released so that it does not accidentally engage. When the weighted handle is raised and the holding brake is released, the centrifugal brake will engage automatically when the winch drum reaches a preset rotational speed in the downward direction. This will ensure that the boat is lowered in a controlled and smooth manner.
It is probably easy to understand that lowering the boat with the holding brake disc partially engaged will cause the brake lining to wear down due to excessive friction, but it may not be obvious how this practice negatively affects the centrifugal brake. So, if you lower the boat while the holding brake disc is partially engaged, the brake lining will wear down. The centrifugal brake never reaches the fixed rotational speed necessary for engagement when the motion of the lifeboat is controlled solely by the holding brake. As a result, the brake pads spin, but they do not make contact with the drum, which prevents the brake from functioning properly.
The brake is enclosed, and provides reliable operation in all climate conditions. When the centrifugal brakes are employed as they were intended to be, the shoes rotate outward and make contact with the drum.
The winch brakes of a launching appliance shall be of sufficient strength to withstand:
- a static test with a proof load of not less than 1.5 times the maximum working load; and
- a dynamic test with a proof load of not less than 1.1 times the maximum working load at maximum lowering speed.
However, apart from these above mentioned tests, the breaks should be annually inspected, serviced and surveyed .
Because the centrifugal brake is hidden from view, utilizing the braking system of your lifeboat davit in the correct manner may not come naturally to you, therefore training is necessary in order to accomplish this task safely.
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Source and Bibliography:
- YouTube video training credit – Marine Online; DG E LEARNING ADU ACADEMY; ShipTech Media; ZeQue Dayrit
- Photo credit: chiefengineerlog.com