Purchase. A purchase is a combination of blocks or pulleys rove with a rope, wire or chain.

Tackle. A tackle is a purchase consisting of a rope rove and through two or more blocks, in such a way that any pull applied to the hauling part, is increased by an amount depending upon the number of sheaves in the blocks, and the manner in which the rope is rove through them.
The whole rope used in a purchase is called a “fall” and the size of the tackle is described by the size of its fall, ie a 20 millimetre gun tackle. In the sketch below the various parts of the tackle are shown.

Parts of a tackle.

The following are the most commonly used tackles:

• Single whip – A rope through a single block.
• Double whip – Two single blocks.
• Gun tackle – Two single hook blocks.
• Handy billy – A single hook block and a double tail block.
• Watch tackle – A double hook block and a double tail block.
• Double purchase – Two double hook blocks.
• Three fold purchase – Two treble sheave blocks.

Single whip. A rope rove through a single block in any position. No power is gained.

Single whip.

Double whip. A rope rove through two single blocks (upper block a tail block, the lower one a moving block). Power gained is double ,ie the weight of one unit on the hauling part will balance a weight of two units on the hook block.

Double whip.

Gun tackle. Two single blocks. Since the moving block is rove to advantage the power gained is three. If the right hand block had been the moving block, the power gained would be two since the tackle would have been rove to disadvantage.

Gun tackle.

Handy billy/jigger. A small tackle for general use, a double block with a tail and a single block with a hook. Power gained is either three or four.

Watch or luff tackle. Double hook block and a single hook block. If rove to advantage, the power gained is four, but if it is rove to disadvantage, the power gained is only three.

Watch tackle.

Double purchase.  Two double hook blocks.  Power gained is either four or five.

Double purchase.

Three fold purchase. Two treble sheave hook blocks. Power gained is either six or seven.

Three fold purchase.