If you need to lift a heavy load, a block-and-tackle pulley system might make your job easier. A block-and-tackle hoist can magnify the force you input into the pulling rope, so that less force is needed to lift the same weight. This magnification of input force is called "mechanical advantage." A simple pulley system is not difficult to construct, using items that are easily purchased at mountaineering shops or over the internet.
Purchase two double-pulley blocks. Links for online purchase are provided in the Resources section below.
Attach one of the pulley blocks to the load to be lifted. The block will have two eyelets, one on each side. Attach the pulley to the load through one of these eyelets.
Attach an eyelet of the other pulley block to a support above the load.
Thread end one of the line or rope (tackle) through one of the two wheels of the hanging double-wheel block. Specifically, fit the line into the groove of the pulley wheel so that the line is making contact only with the top half of the wheel.
Pull that same end through the hanging pulley block enough so that you can thread it through one of the pulley wheels of the block attached to the load. To picture this, the line will be making contact only with the underside half of the load-attached pulley when the entire line is eventually pulled taut.
Thread the end again up over the second (empty) pulley of the hanging block, pull a large length through again, and then thread the second (empty) pulley wheel of the load-attached block.
Thread the end up again to the hanging block, and knot it to the (empty) eyelet on the bottom of the hanging block. Now pull on the opposite end of the line and lift the load. The number of times the line doubles up gives you a mechanical advantage of 4 to 1.
If you use more blocks, you can gain more mechanical advantage and lift your load even more easily.
Tips and warnings
- If you use more blocks, you can gain more mechanical advantage and lift your load even more easily.