The best winch pulley: the Thompson Pulley Block

Winch owners who actually put their winches to use—or who at least learn how to do so—are familiar with some form of the winch pulley or pulley block (also called a snatch block even though it has nothing to do with snatching as we know it). In its most well-known application, a winch line run out through a pulley attached to a stationary anchor, then back to the vehicle, essentially doubles the power of the winch, while reducing line speed by half. If you attach another pulley to the vehicle’s bumper and run the line through that and back to the anchor where the first pulley is attached, you again multiply the power of the winch while again reducing the line speed. It’s a matter of simple physics, but seems like magic. I often use a pulley when winching even when the extra power is not needed, for the sole purpose of slowing down what can be a fraught procedure.

A pulley can also be used to re-direct a pull, for example if you need to winch another vehicle but cannot place your own directly in line with it. A pulley attached to an anchor will allow you to winch around a corner, as it were. In this case the power of the winch and line speed are not affected. The easiest way to determine if the system is multiplying power is to count the number of line sections that are shortening when the winch is working. If you run a line from your winch through a pulley to a stuck vehicle, only the section between the pulley and the stuck vehicle will shorten, thus the system is operating at a 1:1 ratio. When the line is run from the winch through a pulley and back to the vehicle, both lines will shorten as the winch pulls the vehicle, thus the ratio is 1:2 (minus inevitable minor friction in the system).

Brief aside: There is a myth floating around that the diameter of the pulley, and its actual rotation, has an effect on the multiplication of force. This is easy to disprove. Imagine you insert a pulley in your system four inches in diameter, then for comparison another ten times that, or 40 inches. If you pull in one foot of line using the four-inch pulley, the line on the other side will also move one foot. Do the same with the 40 inch pulley and the same thing will happen—one foot of movement for one foot of pull. The only difference is that the four-inch pulley will make a complete revolution while the 40-inch pulley will only make about one-tenth of a revolution. Thus one could argue that the four-inch pulley will experience slightly more load/friction on its bearing surface, but in the context of overall load on a winch system this is insignificant. Likewise, you can drag a winch line around a completely frozen pulley incapable of rotation and it will still multiply the pull of the winch; you’ll simply lose significantly more through friction—obviously not a great idea (see Yankum below). The point is, as long as you’ve changed from having one length of line shortening to having two shortening, you’ll be multiplying the force of the winch.

Winch pulleys have evolved several times over the past few decades. Originally they were heavy—six or seven pounds—with steel side plates and sheave (the rotating bit), intended for steel winch cable. They had to be secured to the anchor with a steel shackle due to the sharp edges.

With the advent of synthetic winch line several companies introduced modified versions of the standard block. ARB’s 9000, for example, incorporates a polymer sheave specifically designed for synthetic line, while otherwise retaining the standard configuration, including the requirement for a steel connecting shackle. Another company, Research in Recovery, experimented with a pulley incorporating aluminum side plates to save weight (lowering the mass in a winch system is always a good idea in case a component failure turns everything in it into projectiles). This pulley (or its twin) is now sold by Safe-Xtract. It’s half the weight of most steel pulleys.

About eight years ago a truly revolutionary winch pulley made quite a splash in the 4x4 community. As conceived by ex-Camel Trophy team member, forester, and military trainer Andy Dacey, the recovery ring was a shockingly simple, one-piece, donut-shaped pulley with a deeply scalloped hole through the center. It was a quarter the weight of any previous pulley and had zero moving parts—perfect as a foolproof, low-mass recovery device for military patrols in hostile regions. It was designed to use a synthetic shackle as both the attachment and the bearing—the pulley rotated inside the loop of the shackle.

It was one of those why-didn’t-anyone-think-of-this-before? innovations, and soon approximately a zillion copies flooded the market. (These included the Yankum offset design which, inexplicably, is designed not to rotate. This is supposedly to save wear and heat build-up on the shackle, instead, um, transferring wear and heat build-up to the winch rope.)

That anomaly aside, the recovery ring was not immune to criticism, both legitimate and otherwise. Some worried about that friction between the Dyneema shackle/bearing and the aluminum, since the pulley slides over the shackle, sometimes under tremendous pressure. One tester (in Australia if I recall) claimed his testing showed the friction inherent in the recovery ring parasitized a shocking amount of the winch’s output, although I never saw this result replicated—in my own tests I comfortably rested my hand on the aluminum even after a strong pull. Nevertheless it’s logical that the ring sliding around on a Dyneema shackle must introduce more friction than a sheave riding on a bushing or bearing. Also of (occasional) concern was the recovery ring’s tendency to catch the winch line between the pulley and the shackle when tension (and the attention of the operator) was lost. Factor 55 added rubber spikes to their ring to alleviate this—a band-aid approach that helped somewhat.

It is certainly fair to say that every type of pulley available until now could be criticized on one or more counts. Most are heavy. Most need a steel shackle as a connector to the anchor or vehicle. Some (not just the ring) can lose the winch line between the pulley and side plate, potentially causing a jam or damage to the winch line. The side plates on most pulleys do not extend far enough to adequately shield the winch line if they come in contact vertically with the ground. Field servicing on many requires snap-ring pliers.

All this was on Richard Sheridan’s mind when he introduced the Thompson Pulley Block. Sheridan runs Freedom Recovery Gear in Pritchart, B.C., Canada, where the “Tommy Block,” as it’s also known, is manufactured.

The side plates of the Thompson Pulley Block (I’ll call it the TPB or just Thompson ) are made from an injection-molded, fiber-reinforced composite. They incorporate extended lips that shield the winch line even if the pulley winds up lying vertically on the ground under tension. They also include molded-in angle guides indicating the mechanical advantage (or lack thereof) of various pulls from zero degrees to 120 degrees—a handy and useful reference. Finally, two loops positively anchor the included soft shackle that comprises the pulley’s anchor. This, combined with the close tolerances between the sheave and side plates, means it is virtually impossible to catch the winch line between the moving parts—I tried with the worst technique I could and failed to do so.

The sheave and axle of the TPB are hard-anodized 6061 aluminum (designed for synthetic line only), and the bushing is something called aluma-bronze, with self-lubricating graphite inserts. The matched synthetic shackle (WLL 13,100 pounds, MBS 65,500 pounds) allows direct connection to a tree-saver strap or a bumper shackle mount with a synthetic-appropriate radius in the opening. With the shackle the Thompson is a commendably light 3.2 pounds. The working load limit is 13,100 pounds, and the minimum breaking strength is 52,500 pounds, a 4:1 safety factor. Both ratings are properly molded into the side plate (the shackle has its own tag). If you need to disassemble the pulley in the field, you’ll find the side plates secured with stainless spiral locking rings. They’re safely recessed, yet all you need is a small screwdriver or knife tip to remove them.

Every once in a while when I receive a new product to review I can recognize as soon as I take it out of the packaging that it’s going to perform exactly as advertised. The Thompson Pulley Block was one such product. (Full disclosure: It had been enthusiastically recommended to me by friend and ex-Camel-Trophy team manager Duncan Barbour, and I also trust Duncan for his critical eye.) Indeed: the design, the workmanship and tolerances, the incorporated shackle, the weight, all had me nodding with the assurance the TPB would meet expectations. And field trials proved just that. The all-in-one design made rigging fast and secure. I didn’t have to keep checking to make sure the line didn’t foul when the rig went slack. I could concentrate on the rest of the operation, confident the pulley was doing its job.

The configuration of the Thompson Pulley Block, with the synthetic shackle running through the axis of the sheave, allows the construction of a three-to-one rigging system employing a synthetic becket. A becket, in pulley (rather than archbishop) terms, refers to a secondary eyelet like the one here, used to reeve multiple-pulley systems with one end of the line attached to one of the pulleys.

Courtesy Balance Community

With Richard’s becket kit—comprising an eight-foot length of Dyneema with a loop on each end and guard sleeves at the right points, plus a short soft shackle—it’s easy to rig a becket on a TPB: From a shackle on the end of the winch line, the becket goes up through the pulley’s shackle on one side, loops back through the shackle on the winch rope, up through the other side of the pulley block’s shackle, and back to the winch line.

With the becket pulley attached to an anchor and another pulley on the vehicle, the winch line runs through the anchor pulley, back through the pulley on the vehicle, and to the becket, giving a three-to-one mechanical advantage. It’s more compact, and easier than using standard pulleys in a three-to-one system, where the winch line has to be secured to a second anchor adjacent the primary pulley.

The Thompson Pulley Block lists for $295 Canadian, which at current exchange rates is about $215 U.S. Considering the added value of the included soft shackle I find that very affordable—and until August 31 Richard has a substantial 25-percent discount in place.

I’m still a fan of the recovery ring and its ultimate simplicity. But give me the choice of just one winch pulley and hands down it’s now the TPB. It’s going in the recovery kit of my main training vehicle, the FJ40, as well as our Troop Carrier. Highly recommended.

Freedom Recovery Gear is here. The 3:1 becket kit (for which you’ll of course need a second pulley) is here.