Sheepshank

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Sheepshank
Sheepshank knot.jpg
An unloaded sheepshank tied in nylon rope.
Category shortening
Efficiency 46%
Origin 1627[1]
Related Catshank, Dogshank
Releasing Non-jamming
Typical use Provides a block and tackle to tighten a rope, shortens or removes slack from a rope, bypasses a frayed section of rope
Caveat Spills if not under tension.
ABoK #1152 - #1154


The sheepshank is a type of knot (or, more accurately unknot) that is used to shorten a rope or take up slack. The knot has several features which make it suitable for this purpose:

  • It provides two loops, one at each end of the knot which can be used to pass another rope through
  • The knot remains secure under tension; the coarser the rope the more secure it is (see Disadvantages, below)
  • The knot falls apart easily when tension is removed

The last of these attributes is invaluable. Other knots will bind tightly and be almost impossible to undo if the knot has been placed under great tension. The sheepshank, by contrast, comes apart quite easily.

Construction Methods

A sheepshank knot may be constructed as follows:

  • Pull a section of rope back and lay it alongside the rope, so that the rope forms a Z approximately 20 cm long.
  • Flatten the Z so that there are 3 sections of rope lying alongside each other, with two U-bends where the rope reverses direction.
  • At each U-bend, grasp the U-bend in one hand, thus holding two of the rope sections. With the other hand form a small loop in the remaining section and draw it over the U-bend so that the loop forms a half hitch and stays there if the free end of the rope is pulled taut.
  • Repeat at the other U-bend.


An alternative method for quickly constructing a sheepshank is as follows:

  • Create a simple loop in the rope, so that the (left) leading end is on top of the (right) trailing end of the loop.
  • Repeat this process further down the rope to create 3 total loops that overlap slightly (similar to a venn diagram with three circles).
  • Reach through the outer two loops and grab either side of the middle loop and pull outward while also keeping the rest of the rope slightly taut.
  • Once the middle loop is pulled through the outer loops, pull on the free ends of the rope to secure.

The result is a flattened loop which is held at each end by a half hitch. If the sides of the flattened loop are pulled away from each other, the flattened loop ends pull out of the half hitches and the knot falls apart, but if the free ends are pulled taut then the knot remains secure.

Usage

Sheepshank knots may typically used for securing loads to trucks or trailers, and in sailing applications.

Example use, such as in tying down a load on a truck, is as follows:

  • Start with one end of the rope tied in a clove hitch around a rail. If the rope is reasonably coarse and this clove hitch is held under tension then it will remain secure.
  • Pass the rope over the load, around a rail on the other side of the truck and back over the load to near the original clove hitch
  • Pull the rope reasonably taut and then form a sheepshank about one meter from a rail on the side of the truck.
  • Pass the free end of the rope around the rail on the side, then back through the loop on the sheepshank nearest the rail, then back to the rail.
  • Pull hard on the free end of the rope to tighten it. The structure of the knot provides a leveraging effect like a block and tackle, so that considerable tension can be brought to bear to secure the load.
  • When the tension is sufficient to secure the load but not damage it, pass the rope around the rail and tie it in a series of half hitches. If the rope is likely to bind and be difficult to untie then use a loop of the free end, so that each half hitch can be undone by pulling on the free end of the loop.


Other knots which may have similar uses are the clove hitch and half hitch.

Disadvantages

The sheepshank was developed before the use of modern "slippery" synthetic ropes. Constructed from such ropes, under load, it can fail. It is strongly advised that one test the knot under load before trusting it.

Variants

Man-o'war sheepshank

The man-o'war sheepshank is a sheepshank knot with a Handcuff knot in the middle. This configuration with the half-hitches formed close to the central knot is used in rope rescue and is called a Fireman's chair knot.

Man-o'-war-sheepshank.png

External links

References

  • Chiang Kai Shek College (September 13, 2005). Basic Knots. Retrieved November 6, 2005. Section 9 has an animation of the Sheepshank being tied that demonstrates that the ends need not be accessible.
  • Scouting Resources. Sheepshank. Retreived December 11, 2006. Shows diagrams with accompanying text.


Footnotes