How to Use a Pulley Winch Block Tackle

The block and tackle has many uses aboard.

Mechanical advantage, when talking about a pulley system like a block and tackle, refers to how much the system will reduce your effort. An ancient system of pulleys--called "sheaves," when in a block--with rope passing through them to move a great weight, many think of the block and tackle as a shipboard item, once used to haul sails aloft. A block and tackle has more uses aboard than hauling sail, however. Once you learn to use it, you'll find your work is easier.

Instructions

1. Compare the size of the rope with the size of the blocks through which it's reeved. If the block is reeved--reeve is a technical term meaning "to shove something through a hole or gap"--with fiber line, like nylon, the block should be three times the circumference--not the diameter--of the rope. For example, a line that's 3 1/2 inches around requires a 4-inch block; where the circumference includes a fraction, round up to the next larger whole number.

2. Compare the weight of the load with the safe working load of the rope reeved through the blocks. An old rule of thumb is to multiply the diameter of the rope by itself and multiply the result by 2,000 to determine the number of pounds a rope can safely hold: for a 1/4 inch diameter fiber line, multiply 0.25 by itself (0.625) and by 2,000; the result, 125 lb., is the safe working load of the line.

3. Hook the block with the working end of the line, the line you pull on, to the load and the block and tackle is said to be rove to advantage: each part of the line rove through the blocks contributes to the lift. If you are using a pair of blocks with two sheaves (a twofold purchase), the mechanical advantage is four-to-one instead of three-to-one: if the load weighs 100 lb., your effort will be the same as lifting 25 lb. This works well when you are raising a lift to you from a lower level.

4. Secure the block with the working end of the line to a fixed point, rather than to the load, and the block and tackle is said to be rove to disadvantage: The working end of the line no longer contributes to the lift. If you are using a twofold purchase, the mechanical advantage is three-to-one and that 100 lb. weight requires the effort of lifting 33 lb. This suitable when you are raising a lift from your level to one above.

5. When you insert the hook of a block through the the ring set in the overhead support or the lifting element of the load, "mouse" the hook by tying a loop in the end of a piece of rope (called a mouse), dropping the loop over the point of the hook and wrapping the rope horizontally around the back of the hook and back to the point not less than three times. After wrapping around the hook, wrap the end mouse line three times, vertically, around the three horizontal wraps and allow "the mouse's tail" to hang loose.

Tips & Warnings

• To find the mechanical advantage, count the number of moving parts of rope in the moving block to which power is applied; the line from the moving block that's belayed to the stationary block doesn't count because no power is applied to it, only strain.

References

• "The American Merchant Seaman's Manual"; W. Hayler; 1981