A block and tackle , sometimes known as a sheave block or rope pulley, is a useful pulley system that can be used to lift heavy weights or transfer forces in different directions. This handy system can be used in construction, in a theatre or even in a gymnasium, as this little device can do so much.
It is simple, efficient and easy to use, which is why it is used in so many different contexts all over the world. But, what are block and tackles? How do they work?
When you take a look at one you will see the anchor hook at the top of the pulley system that the ropes are fed through, that can be attached to a secure, solid structure. A block and tackle can have more than one sheave to use with multiple ropes.
Each rope can work independently of one another, but all together, they become a central pulley system that creates a strong force to move heavy objects up and down or suspend them in the air. Although we now use pulleys for so many different things, they came into popular use on sail ships, but date back all the way to the ancient Greeks.
Once you have set up your block and tackle and secured the anchor, simply pull on the single rope. Although there may be various ropes fed through the sheaves, when one is pulled it will create a huge transference of force over the pulley, to make ling heavy objects much easier.
The way a block and tackle works is that it is a transference of force. Each rope that is used in the pulley creates an extra force that can be used to lift heavier loads. For example, say the pulling rope leading off the pulley system is being pulled on using a force of one pound, this is transformed into a total force of four pounds, if there are four ropes used in the block and tackle.
This means that you can pull on the block and tackle, then your efforts will be transferred into an even stronger force, enabling you to lift more weight. A two rope pulley is called a gun tackle, one with three ropes is called a luff tackle and with four ropes, it is called a double tackle.
This ingenious little contraption is easy to transport and can be used in lots of different situations. Simply neatly packing it away is an ideal way to transport it, as there is no need to take it apart and put it back together again if you need to use it somewhere else.
A block and tackle can be used in different ways, multiple Sheave blocks can be used in the same operation in order to change direction of pull and to increase the pulling power. This is known as the sheave block technique.
By doing this, you can adjust the direction of where the single rope needs to be pulled to create the force.
This image shows how multiple blocks are used in conjunction with a wire rope cable puller in order to increase the pulling power.
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