The sometimes surprisingly massive blocks seen aboard sailing ships (as in the picture above from Getty Images) are readily recognizable even to lubbers. They are understood to be part of a ship’s rig but ask anyone what they actually do or what the individual parts of this system of pulleys might be called and you may get no more than a shake of the head. Here’s a little insider information on these ancient machines as they relate to ships and shipping.
Blocks are oval pieces of wood with wheels commonly referred to as sheaves inside them. They are used to facilitate the movement of most, if not all, of the running rigging on sailing ships. They are therefore responsible for the setting of sails to the ship’s best advantage as long as she is at sea.
These pulleys come in a number of sizes and, as is so usual at sea, each has a name. A single block has one sheave, a double has two, a treble has three and a fourfold block has four. A fiddle block has two sheaves, one on top of the other, which makes it look rather like a violin or viola. Other forms of block include a cheek block which has a wooden guard, or cheek, on only one side of the sheave. The other side is mounted flush to a surface, like the gunnels. A shoe block has two sheaves that turn at right angles to one another. A snatch block has a strap that allows the cheeks to be opened for maintenance to replacement of the sheave inside.
Blocks can also be called by the name of the rope they carry so that there are clue-line, halliard, brace, blowline and so on blocks. With regard to manufacture, a block is termed a made block when it is put together from separate pieces which include the shell or cheeks, the sheave or wheel, the pin or axel on which the wheel turns (generally made of iron) and the strop, a rope by which the block is attached to its stations. A morticed block, on the other hand, is chiseled out of a single piece of wood.
A block can be used on its own or with a tackle, which is essentially another block that will allow a single man to lift far more weight than he would be capable of lifting without the mechanisms. The Sailor’s Word Book of 1867 explains it this way:
When a power sustains a weight by a rope over a fixed sheave, the weight and power will be equal; but if one end of the rope be fixed, and the sheave be movable with the weight, then the power will be but half the weight; but in a combination of sheaves, or pulleys, the power will be to the weight as 1 to the numbers of parts of the fall [rope].
The mathematical formula involves three steps. First, determine the amount of weight one part of the rope must life. Next, multiply this by the number of parts at the sheave of the block. Finally, subtract one quarter from this amount to account for resistance. This sort of calculation was done daily on any ship with sails, making the image of the ignorant sailor – particularly aboard a pirate or privateer as we are so often led to believe – a bit of a stretch if you ask me.
Keeping blocks in good working order was an absolute necessity and would have been part of daily maintenance on any ship. As with so many other things, a ship is only as good as her rigging and the myriad blocks she carried would be a vital part of same.