Besides adding mechanical advantage to the running rigging, blocks are used to change direction of the line passing through them. Conventional blocks must be attached to something in order to work, and the most common method used is by a shackle that is usually an integral part of the block. 6-1 shows the difference between front and side shackles, but the trend is to fit blocks with adjustable shackles which can be mounted either with a front or a side shackle using just one block or with a swivel shackle. A front or side shackle is used to keep the block in one position or plane of reference, whereas a swivel shackle allows the block to turn to any position. Not all blocks have all of the above parts.
Some blocks have shackles that swivel or are adjustable to either side or front shackle locations.
Dear Glen, Re, Jack Tar Plywood Version P lease find enclosed photographs of Jack Tar's progress, for your archives. She is beginning to look very nice and is admired by all in our village. As you can see, I have made a few personal changes to your design, but structurally, the hull, main cabins, and bulkheads are strictly to your plans. The teak decks on the Jack Tar look really good. At the moment I am fitting the fly bridge and teak decking that area.