Simply put, a block in sailing, is a single or multiple pulley used as a lever to maneuver loads of rigging usually attached to fixed and running applications on a ship. In use one block is connected to a fixed surface. A rope or line is woven through the sheaves of that block, and maybe through one or more matching blocks at some far end to make up a tackle.
Due to the size of a model ship, blocks that are used are generally representations of blocks -a fairly poor representation at best! However it is quite difficult to make accurate museum quality blocks. Also the types of blocks represented in kits are typically limited to common blocks, sister or violin blocks, heart and ramshead blocks. Other types of blocks, deadeyes, hearts and bull’s eyes will be touch upon.
Following is a general description of the construction of blocks used on ships.
The shell is the outside case of a All Round Shipping block, and is made of ash, elm, or iron. In ship model kits, the shell is typically mad of walnut or boxwood. The shell could be made in one piece or assembled from several components -which was always made of wood until the middle of the 19th century. After this time the shell was occasionally made of metal. A block consists of a shell that is made in one piece or assembled from several components -which was always made of two until the middle of the 19th century. After this time the shell was made in one piece.
The shell contained a pulley, or sheave, over which the rope ran, and which rotated on a pin. The sheave is the wheel on which the rope travels, and is made of metal, lignum-vitae ( wood that has the extraordinary combination of strength, toughness and density), or iron. The Bouch is made of metal or leather, and is the centre piece of the sheave which travels on the pin. The Pin is made of iron or lignum-vitae, and has a head at one end: it passes through the centre of the shell, and the bouch of the sheave. In ship model kits, the sheave and pin are usually brass.
The crown and tail of a block are the ends of the shell; the latter is easily known, as it has a much deeper score than the former to receive the splice of the strop, and in most cases the standing part, of the purchase. The Swallow is the open part between the sheave and shell.
The Score is the groove in the outside part of the shell to take the strops either single or double scores, according to what the blocks are required for. Double-scored are always double-stropped.
The size of a block is denoted by the length, and its classification by the flatness or thickness of the shell, the number of sheaves, the number of scores, and the quality of the stropping. A block, if one sheave, is called a single block; two sheaves, a double block; three sheaves, a treble, and so on, according to the number of sheaves. If one score, it is termed a single score block; if two scores, a double scored block etc.
A block is supposed to carry a rope one-third its length in circumference: that is to say, a 3mm. block would carry a 1mm. rope, a 6mm block would carry a 2mm. rope etc. Blocks are designed for use with a certain size of rope. Therefore, they should never be used with rope of a larger size. Rope bent over a small sheave will be distorted, and any great strain applied will damage it and may even result in the rope wearing on the frame.
Determining the size of block to use with wire rope is impossible because of the factors involved. However, experience has shown that the diameter of a sheave should be at least 20 times the diameter of the wire rope. An exception to this is flexible wire for which smaller sheaves can be used because of their greater flexibility. The construction of the wire rope has a great deal to do with determining the minimum diameter of sheaves to be used. The stiffer the wire rope, the larger the sheave diameter required.
Types of Blocks
Are used for nearly all common purposes, reeving purchases, boats’ tackles, gun tackles, etc., quarter blocks, span blocks for topmast studsail halyards, and peak brails, jewel blocks at the topsail and topgallant yard-arms for the studsail halyards, and in fact, for most of the running gear.
Sister blocks are tapered, the upper part of the block being smaller than the lower part, having a deep score, as they are seized between the foremost pair of shrouds in the topmast rigging; they are thus constructed not to interfere with the spread of the rigging; they are also two in one on end, the reef-tackle being rove through the upper, and the topsail lift through the lower sheave, they are sometimes fitted in separate pendants.
Ramshead blocks were used to raise and take down the lower yard in order to furl and unfurl the sails. The practice of moving the lower yard ended around 1660. The ramshead block allowed for a few feet of clearance when the yard was raised or lowered.
Upper Masthead Jeer Block
A jeer block is a double block, double-scored, stropped with two single strops, the four parts – or that is, the two parts of each strop – are seized together at the crown of the block, leaving two long bights or eyes, which are passed up through the after hole in the fore part of the top, and lashed on the after part of the mast head.
Every block on board a ship has a purpose. There are at least 10 other blocks not described in this article. However in most ship model kits, you’ll only find three or four types of blocks that are to represent all blocks.
A few words on specialty blocks. We’ll discuss dead eyes, hearts and bulls eyes in another article