The primary function of the snatch block is to change the direction of the load or pull. The advantage of a snatch block over the other types is that it can be opened and a bight of line placed over the sheave without passing the end of the line through the swallow. The snatch block has a hinged cheek on one side and differs from all the other blocks.A swivel-hook block is a single- or multiple-sheave block with a swivel hook that allows the lock to move in the direction of the load.A fixed-hook block is a single- or multiple-sheave block with a stationary hook attached to the top of the strap.It also may or may not have a hook or becket. The multiple-sheave block contains two or more sheaves.The single-sheave block has only one sheave and may or may not have a hook or becket.These blocks are explained below and illustrated in Figure 6-3. Wooden and metal blocks are of the same design except for the head or heel block which is only metal. There are several different types of blocks, each with a particular use. This figure shows the diamond and roller bearing block.Ħ-4. The parts of a metal block are shown in Figure 6-2. The metal block has bolts to hold its cheeks together and a metal shell. Metal blocks have basically the same part as wooden blocks. The entire wooden portion of a block is called the shell it protects the sheave and line.Ħ-3. Line is never passed through the breech of a block except for a small tail line used to keep the block from bouncing on the deck. The breech is the opening between the bottom of the sheave and the block and serves no definite purpose. The opening between the top of the sheave and the block where the line is passed through the block is called the swallow. The front of the block is called its face and the sides of the shell are called cheeks. The becket usually has a thimble to prevent chafing of the line. The strap may continue through the block and form a projection, called the becket, to attach another line. Personnel may suspend the block or apply a load by means of a hook or shackle inserted in the top of the strap. Each block has one or more steel straps which strengthen the block and support the sheave pin. A wooden block, as shown in Figure 6-1, consists of one or more sheaves (pulleys). Section III covers marlinespike seamanship, which is a general term for handling and caring for fiber line and wire rope used aboard ship or in other marine operations.Ħ-2. It details the care and use of wire rope, procedures for computing the safe working load and breaking strength, and inspection and handling. Section II covers elements of wire rope rigging which cargo handlers in a terminal service company must know. Section I of this chapter discusses blocks which are among the most important fittings used aboard ship on the deck, in the engine department, and in other operations.
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