When reeving tackles reeve each type differently. If a tackle is rove improperly, too much friction and possible binding of the falls can result when lifting or lowering a load, creating a safety hazard. It is important to use the proper method of reeving each type of tackle up to and including a threefold purchase.
In reeving triple blocks, you should put hoisting strain at the center of the blocks to prevent them from inclining under the strain. If the blocks do incline, the rope will drag across the edges of the sheaves and the shell of the block and cut the fibers.
Single whip tackle offers no mechanical advantage and runner tackle has a 2 to 1 mechanical advantage.
GUN TACKLE - Place two single-sheave blocks about 3 feet apart with the hooks or straps facing outboard and both blocks in the same position, either on their face or cheek. Next, they should run the line through the first and second block, then splice it to the becket of the first block. Gun tackle has a 2 to 1 mechanical advantage.
LUFF TACKLE - Position one single- and one double-sheave block the same as the gun tackle. Run the line through one of the sheaves of the double-sheave block first and then to the sheave of the single-sheave block. Next, run the line through the other sheave of the double-sheave block and splice the line to the becket of the single-sheave block. This tackle offers a 3 to 1 mechanical advantage.
TWOFOLD PURCHASE - Position two double-sheave blocks in the same manner as with the luff tackle. Reeve the line through the top or bottom block, stay in sequence, and never cross from one side to the other. After reeving the tackle, splice the standing line to the becket. Twofold tackle has a 4 to 1 mechanical advantage.
DOUBLE LUFF TACKLE - Obtain a double- and a triple-sheave block. Place the blocks 3 feet apart with the hooks or straps facing outboard and position the blocks so that one is face down and the other cheek down. When reeving a tackle that has one block with more sheaves than the other, always start with the block with the most sheaves. In this case, start reeving through the center sheave, keeping the line parallel. Never cross from one side to the other. Double luff tackle has a 5 to 1 mechanical advantage.
THREEFOLD PURCHASE - Place two triple-sheave blocks 3 feet apart, with the hooks or straps facing outboard, positioning the blocks so one is face down and the other is cheek down. Start reeving in the center sheave of one block and finish in the center sheave on the other. Then splice the standing part to the becket. This tackle offers a 6 to 1 mechanical advantage.
