PartsBlock and tackle (pronounced taycle) was much more common not so long ago, before boats had winches, back when block and tackle was the best way to obtain a mechanical advantage. It works on the same principle as the lever and fulcrum, using range of motion to multiply the applied force. (bottom). The fastening ring attached to of a the crown is called an eye. If there is one block attached to the tail, it is called a becket. The side surface of the block is called a cheek. The round part that rotates on a pin mounted between the cheeks is called a sheave (rhymes with "give"). It has a score or valley that is semicircular, to take ordinary rope, or v-shaped and perhaps with a groove at the bottom, for wire rope.
When moving two blocks apart, to increase the length of the tackle, you are said to overhaul it. The opposite of this, hauling the fall without load to move the blocks closer and shorten the tackle, is called rounding in. When the blocks are as close as they can get, the tackle is two-blocked or block-and-block.
advantageWhen threading line through a Reeving to block, you reeve it. Pictures commonly show two blocks that are rove with their cheeks parallel, but in fact, usually the cheeks will line up with one block perpendicular to the other. The line that reeves a block, called the fall, has a fixed or standing end and a free or hauling end. The block itself can be fixed or movable. Most often, one block is fixed and the other movable. When the hauling end leads to a movable block, the tackle is said to be rove to advantage. When the fall leads to a fixed block, the tackle gives less of a mechanical assist, the fall has less range of motion, and it is rove to disadvantage. Since mechanical assist is usually wanted, tackle is rove to advantage whenever possible except when wanting to reduce the travel of the hauling end. each block, reeving should begin and end near the middle so that the block does not lean to one side when hauling force is applied. Begin reeving at the block that has one sheave more than the other block. If both blocks have the same number of sheaves, begin at the block that has a becket, so that you can end at the becket.
As they run between sheaves on the two blocks, lines must not cross over. This means that if you insert an oar between the reevings of line on either side of the sheaves, you can raise it to touch the upper sheaves and then drop it to touch the lower sheaves without trapping any line between the oar and the sheaves. Lines will still cross one another on either side of your oar, naturally, since you began with the middle sheave and must cross at some point to reach both of the end sheaves. Saying that lines must not cross is the same as saying that line is always rove through the block in the same direction on every sheave of that block. It passes in the opposite direction through the other block.
For two double blocks (with two sheaves each), if the blocks are labeled A and B, and the sheaves are numbered 1 and 2, the reeving will be A1, B2, A2, B1. With triple blocks, use A2, B1, A3, B3, A1, B2. With four sheaves, use A2, B3, A3, B4, A4, B1, A1, B2, and so on.
Sheaves are found in other places, besides blocks, where line must change direction. There will be halyard sheaves at the masthead, for example, and perhaps reefing line sheaves at the end of the boom. Devices similar to blocks, called piece of material, traditionally wood. Despite their many advantages, especially in standing rigging, deadeyes have been replaced by turnbuckles in modern boats because they eliminate the need to belay the hauling end of the line.
Kinds
of
blockThere are many kinds of blocks, literally hundreds. Fiddle blocks have smaller sheaves below their larger sheaves, instead of identical sheaves that share a pin. Cheek blocks have one cheek that can be bolted to a surface, such as the deck or a spar. Snatch blocks have one cheek hinged to free the line when that cheek is opened. Ratchet blocks allow the line to be hauled but then grip it, to prevent running free, when no hauling force is applied. (They are commonly used for furler lines and work poorly, if at all, when rove backwards.) Air blocks have cheeks that are cut away to little more than structural members.