Two Knots for Mechanical Advantage

S1-E9-Trucker's-Hitch-Cover

Creating a Block and Tackle Without Pulleys

Update: After several readers requested further explanation of the mechanical advantage, I posted Physics of the Trucker’s Hitch.

The Trucker’s Hitch is not a single knot, but a knot system that acts like a block and tackle for tightening, hoisting, or hauling loads with mechanical advantage. You’re probably familiar with it, but it’s time to learn a couple of knots that will make this system easy to untie when you’re done, so you don’t have to cut the knot or waste time struggling to untie it. Review your knotting terms in last week’s Survival Tips article, which covers the Pipe Hitch and the Pile Hitch.

Watch the video for instructions (goes live early afternoon Jan 28).

Mechanical Advantage of the Trucker’s Hitch

I need to make a correction. In the video I said that the Trucker’s Hitch creates a 2-to-1 theoretical mechanical advantage, but in the specific configuration demonstrated, it’s actually a 3-to-1 advantage, because both ends of the system are anchored (like when tightening down a load in your pickup truck), which is how you will usually use it. If only one end is anchored, (like when hoisting a zombie up into a tree), that’s when you get only a 2-to-1 advantage.

In this configuration, you gain a 2-to-1 theoretical mechanical advantage

Fig. 1 — Hoisting a Zombie. In this configuration, you gain a 2-to-1 theoretical mechanical advantage

In Figure 1, the first “pulley” is the midline loop, and the second is the Zombie’s neck. The second pulley is not fixed: it moves during the work done, and so you only get a 2-to-1 mechanical advantage.

Fig. 2 -- Stretching a Zombie. In this configuration with BOTH pulleys fixed, you get a 3-to-1 mechanical advantage.

Fig. 2 — Stretching a Zombie. In this configuration with BOTH pulleys fixed, you get a 3-to-1 mechanical advantage.

Figure 2 illustrates how the Trucker’s Hitch usually operates, as when securing a load in your truck or trailer. This is the configuration demonstrated in the video. Here both pulleys are fixed, and you gain a 3-to-1 mechanical advantage. So if you want to stretch a zombie apart, this is how to do it.

Details about the Trucker’s Hitch

When securing a load in the bed of your truck or trailer, the mechanical advantage provided by the Trucker’s Hitch acts like a block and tackle, which allows you to tighten the rope a lot more than you can without it. You can tie the Trucker’s Hitch with several different combinations of knots, but I prefer knots that are easy to untie when I’m done. For the anchor I use the aptly-named Anchor Hitch, and for the midline loop I use an Alpine Butterfly.

The mechanical advantage (whether 3-to-1 or 2-to-1 depending on configuration) is “theoretical” because of friction. In a frictionless setup, all of the force exerted on your end of the rope goes into work on the load. But in the real world we have friction, which “intercepts” some of the work and dissipates it as heat, sound, and degradation of the material (“wear and tear”). Pulleys reduce friction and so are much more efficient. The slicker your rope, the better your advantage.

The Anchor Hitch

This is my go-to knot for securing the end of a rope to a ring, post, or tree branch. No matter how much tension you put on the knot, it is easily cast off when you’re done. I’ve never had it jam or capsize.

Anchor-Hitch

Fig. 3 — The Anchor Hitch

 

The Alpine Butterfly

This one is used for the midline loop (the substitute pulley). In the past, you’ve probably made your midline loop with an overhand knot, and then had to cut the rope or twine because it jammed. Those days are over. Once you learn this knot, you’ll never go back to the overhand. It is not as easily cast off as the Anchor Hitch, but with a little work wiggling the loops on either side of the knot, I’ve always been able to work it loose. Using a very thin twine under great tension, I can imagine a jammed Alpine Butterfly, but that’s an unusual case.

Alpine-Butterfly-Front-2

Fig. 4 — Front of the Alpine Butterfly. Note that the two in-line strands are parallel — they do not cross in the front.

To ensure the knot is easy to untie, you have to work the two in-line strands so they’re parallel in the front and cross in the back. If they cross in the front, the knot can jam, and I’ve heard it can capsize, but I haven’t confirmed that.

Alpine-Butterfly-Back

Fig. 5 — Back of the Alpine Butterfly. The strands cross in the back.

This photo shows the in-line strands correctly crossing in the back.

Practice these knots as demonstrated in the video, and see if you can get them tied in three seconds or less (each, of course!).

~SnoMan

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