Reeving and sheaves: how to multiply winch pull

Every winch has a rated line pull, the force it can put on the rope leaving the drum, but the job in front of you does not always respect that figure. Sometimes the load is heavier than the winch can pull directly, and rather than reach for a bigger machine you can reeve the rope through sheaves and a moving block to multiply the pull. It is one of the oldest tricks in lifting and hauling, and it works as reliably today as it ever did. The catch is that nothing comes free: the pull you gain you give back in speed, and the rope and sheaves have to be right for it to be safe.

More falls of rope, more pull

The idea is simple. Instead of running the rope straight from the winch to the load, you pass it around one or more sheaves so that several lengths of rope, called falls, share the load between them. If two falls of rope support the load, each carries about half of it, so the winch only has to pull about half the load's weight to move it. Add more falls and the load is shared more ways still. The pull at the load is multiplied roughly by the number of falls supporting it, which is how a modest winch can move a load several times its rated direct pull.

How the multiplication works

Picture a load hanging from a moving block with two rope falls running up to fixed sheaves and back. The winch pulls one end of the rope, and because two falls share the weight, the tension the winch must supply is about half the load. Reeve it with three falls and the winch supplies about a third; with four, about a quarter. This is mechanical advantage, the same principle as a block and tackle, applied to a winch rope. The winch does not become more powerful; instead the load is divided among more lengths of rope, so the force the winch needs to overcome is smaller.

What you trade away: speed

Mechanical advantage is a bargain, not a free gift, and the price is speed. If two falls halve the pull the winch needs, they also halve the speed at which the load rises or moves, because the winch must wind in two metres of rope for every metre the load travels. Three falls cut the load speed to a third, four falls to a quarter. This is the heart of reeving: you are trading the speed you do not need for the pull you do. For a slow, heavy lift that trade is excellent, but if the job needs the load moved quickly, reeving works against you, and a winch with enough direct pull is the better answer. Our note on line pull covers how the direct rating is set in the first place.

Sheaves, blocks and the D/d ratio

The sheaves the rope runs over are not just pulleys; their size matters to the rope. Bend a wire rope around too small a sheave and you fatigue and damage it, shortening its life sharply. The relationship is captured in the D/d ratio, the sheave diameter divided by the rope diameter, and lifting practice sets minimum ratios precisely to protect the rope. Larger sheaves are kinder, letting the rope bend gently and run freely. The blocks also have to be rated for the load they carry and reeved so the rope sits properly in the grooves. Reeving well is as much about choosing the right sheaves and blocks as about counting falls.

Friction means the real gain is less

The neat arithmetic of doubling and tripling assumes the sheaves turn without resistance, and real sheaves do not. Each one adds a little friction, so the pull the winch actually has to supply is a touch more than the ideal, and the more sheaves the rope passes over, the more those small losses add up. Two or three falls lose little; reeve through many sheaves and the cumulative friction becomes worth allowing for. It is why a four fall reeve does not quite give a clean four times the pull, and why piling on falls has diminishing returns. Good sheaves on good bearings keep the losses small, but they are always there and honest sizing allows for them.

Reeving it safely

Reeving multiplies forces, and that includes the forces in the anchor points, the dead end and the structure. The fixed sheaves and the dead end of the rope can see loads as high as or higher than the load itself, so they must be rated and anchored accordingly, not just clamped to whatever is handy. The angles the rope makes as it enters and leaves each sheave matter too, because a bad lead angle wears the rope against the side of the groove. And every part, rope, sheaves, blocks and anchors, has to be inspected, because reeving puts more components in the load path, each of which must be sound. Done properly reeving is safe and routine; done carelessly it concentrates forces where you did not expect them.

When to reeve and when not to

Reeve when the load is heavier than the winch can pull directly and the job can accept the lower speed: slow, heavy lifts, occasional outsize loads, situations where a larger winch is not available or not worth it. Do not reeve when speed matters, when the extra sheaves and blocks would clutter a job that a bigger winch would do cleanly, or when there is nowhere sound to anchor the fixed blocks. The honest approach is to size the winch for the everyday duty and keep reeving as the tool for the occasional heavier pull, rather than designing a system that depends on a tangle of blocks for its normal work. We are glad to advise which way round suits your duty.

Sizing the winch behind the reeving

Whether you reeve or pull direct, it starts with the right winch. See the range in our winch catalogue, and read how the drum and rope capacity and the line pull are set, because reeving changes how much rope the drum must hold as well as the pull. Tell us the load, the speed you need and whether you expect to reeve, and we size a winch and recommend the sheaves and blocks to match, so the multiplied pull is delivered safely rather than improvised on site.

Frequently asked questions

How does reeving multiply a winch's pull?

Reeving passes the rope around sheaves so several falls of rope share the load. With two falls each carries about half the load, so the winch pulls about half the weight. The pull is multiplied roughly by the number of falls supporting the load.

What do you lose by reeving?

Speed. Doubling the pull with two falls halves the load speed, because the winch winds two metres of rope for every metre the load moves. Friction in the sheaves also means the real gain is a little less than the ideal multiple.

Why does sheave size matter?

Bending a wire rope around too small a sheave fatigues and damages it, shortening its life. The D/d ratio, sheave diameter divided by rope diameter, sets a minimum to protect the rope, so larger sheaves let the rope bend gently and last longer.

Is reeving safe?

Yes, when done properly. The fixed sheaves, dead end and anchors can see loads as high as or higher than the load, so they must be rated and anchored for it, the rope lead angles kept correct, and every component inspected, because reeving adds parts to the load path.