Lifeboat Davit Testing
Traditionally lifeboat davits were tested using sand bags and a crew of strong AB’s. More recently water bags began to be used making the job considerably easier… you simply place the empty bag in the lifeboat, fill it with water, test the davit, then open the bag’s drain valve (do’t foget the lifeboat’s drain plug!).
For a tender it is:
Maximum number of persons on board: 150
Weight of maximum number of persons: 150 x 75 kg (165.35 pounds) = 11,250 kg (24,802 pounds)
Fully equipped lifeboat: 12,350 kg (27,227 pounds)
Total: 23,600 kg (52,029 pounds)
The test is done at 1.1 times the weight they will carry to ensure the complete construction is solidly connected to the side of the ship (the davit arms themselves are tested at the factory at 2.2 times the weight they will ever have to carry — so much stronger).
The yard connected to the lower blocks a big steel box that is filled with water so it totals the desired weight: the weight of the box and the water 23,600 kg (52,029 pounds) multiplied by 1.1 = 25,960 kg (57,232 pounds).
The weight is read by the crane driver, who has a strain gauge in the control cab of the crane. He radios the information down to the people on deck. The crane then slacks its hoisting wire so the davits take the strain. This is called the static test.
For the dynamic test, the manual brake on the winch is lifted and the box is lowered the same way you would lower the lifeboat (or tender, in this case). The lowering speed is then measured, since this needs to be between .75 and 1.30 meters (2.5 and 4.3 feet) per minute. If the boat lowers too slowly or too fast, the centrifugal speed control brake needs adjusting.
Then, after about six seconds the manual brake is thrown back — full force — and the lowering stops. This is rather spectacular, with the box bouncing up and down, and the bulkheads where the sheaves are connected flexing back and forth. Nobody envies the man who has to operate the brake!
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