How to Make Manual Lifting Easier by Setting up a Block and Tackle Pulley System

A block and tackle pulley system is an arrangement of ropes and pulleys which allows for force to be traded for distance, and can be found in everyday, common applications such as the rigging on a sailboat, flagpoles, window blinds, engine hoists, or even large construction cranes. In the simplest terms, a block and tackle is the combination of rope and two or more pulleys which reduces the amount of force needed to lift a load. It's the increased mechanical advantage (IMA) of a block and tackle system that makes for easier lifting, and the IMA of a block and tackle is determined by the number of times the rope passes through the pulleys. One pulley is equal to one advantage, two pulleys is equal to two advantages, etc. To lift 100 lbs., a one-pulley system would equal 100 lbs. of lifting force required. However, two pulleys would mean only 50 lbs. of lift is needed to lift the same 100 lbs., while a three-pulley system would require only 33 lbs. of lift on the pulling rope.

Recognized by history as one of the greatest "six simple machines" ever created, the first documented use of the pulley was by Greek scientist Archimedes around 250 BC. It's believed that it was almost certainly used in the creation of the famous Stonehenge in the United Kingdom.

History aside, there are six aspects to consider when setting up a block and tackle pulley system: Function, Lifting with a Pulley, Lifting with a Block and Tackle, Mechanical Advantage, Force and Work, and Friction.

A block and tackle system is most often used where a heavy-duty machine would be unavailable to use for heavy lifting. For that reason, man-made lifting power is required and this is where you might see the system used, for example, on a boat with sails (as a heavy-duty crane would be highly impractical to use).

A standard pulley is simply a single wheel on an axle with a rope running over it. For basic lifting of 100 lbs., a single, stationary pulley could be attached to a building's rafters, a rope run through it, and then one end of the rope attached directly to the 100 lb. load. The other end of the rope is for manually pulling on the load to move it. In this instance, every time the rope is pulled one foot with 100 lbs. of force, the load will be lifted one foot. If anything less than 100 lbs. of lifting force is exerted, the load will not be moved at all.

With this setup, a second pulley can be attached to the load instead of attaching the rope directly to the load. Then passing the rope through the stationary pulley attached to the rafters creates a block and tackle system. The rope now travels twice between the rafters and the load each time the free end of the rope is pulled. The rope would have to be pulled two feet to lift the load one foot in the air. However, only 50lbs. of lifting force would be needed to lift a 100 lb. load.

This disparity between the amount of force required to move an object and the weight of the object is the mechanical advantage (or increased mechanical advantage = IMA) of the block and tackle. To calculate the IMA, either divide the weight of the object being lifted by the force required to lift it, or divide the amount of rope that must be pulled. To determine the mechanical advantage of a machine by the first method you would divide the load's weight, 200 lbs. for example, by the amount of force required to lift it, 100 lbs., giving you an IMA of two. Dividing how much rope is hauled at a time, two feet, by the distance the crate rises, one foot, gives the same answer—an IMA of two. Generally, the number of lengths of rope between the two pulleys in a block and tackle corresponds to the IMA of the system or machine. In the block and tackle example above, two lengths of rope passing through two pulleys leads to an IMA of two.

This examines the ratio of work done (pulling the rope) relative to the force created and the lift generated. While the block and tackle can decrease the amount of force needed to move the load, it doesn't change the amount of work. A block and tackle with an IMA of 4 allows a 4 lb. load to be lifted with a single pound of force. However, it requires the rope to be pulled 4 feet to lift the load one foot. 

Finally, the last aspect to consider is friction. Any time an object moves against another, some of that moving object's energy is lost to friction. In the case of the block and tackle, with moving rope and pulleys, friction will reduce the IMA of the machine. Dividing the weight of the object being lifted by the weight necessary to lift it will allow you to figure in the effects of friction on the IMA of the block and tackle.

Since its invention in ancient times, the block and tackle pulley system has endured to become one of the greatest simple machines of all time. If you need to lift or move heavy items using less exertion, setting up a block and tackle pulley system is still the way to go.

Zoro has all you need to create effective block and tackle machines with use of our hoist crane accessories, including pulleys and sheaves for use with wire rope, fibrous rope, and more.

To protect yourself when manually pulling loads by hand, be sure to check out our wide selection of leather palm gloves to ensure an enhanced grip for a safer load-lifting exercise. 

The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.