Heres a good tip. If you count the number of parts of rope going to and from the movable block you can figure the mechanical advantage at a glance. This simple rule will help you to approximate the mechanical advantage of most tackles you see in the Navy.

Many combinations of single-, double-, and triple-sheave blocks are possible. Two of these combinations are shown in figure 2-8.

You can secure the dead end of the fall to the movable block. The advantage is increased by 1. Notice that this is done in figure 2-7. That is a good point to remember. Remember, also, that the strength of your fallropeis a limiting factor in any tackle. Be sure your fall will carry the load. There is no point in rigging a 6-fold purchase that carries a 5-ton load with two triple blocks on a 3-inch manila rope attached to a winch. The winch could take it, but the rope couldnt.

Now for a review of the points you have learned about blocks, and then to some practical applications aboard ship:

With a single fixed block the only advantage is the change of direction of the pull. The mechanical advantage is still 1.

A single movable block gives a mechanical advantage of 2.

If you fix the dead end of the fall to the movable block you increase the mechanical advantage by one 1.