A shear lashing (sometimes spelled “sheer lashing”) is used when two poles are to be opened out like scissors to make what are referred to as sheer legs. The lashing joins two parallel poles at the tips, with the butt ends splayed apart, normally to support some kind of weight. Most always, in Scout Pioneering we use sheer legs to form an A-Frame.
Most frequently, the lashing is formed by staring with a clove hitch around one pole, applying six to eight wraps around both poles, two fraps between the poles, and finishing with a clove hitch around one pole. When the wraps are taken around both poles, the lashing is referred to a Shear Lashing with Plain Turns, which is the quickest and easiest method. On occasion, when the poles will “scissor” back and forth, weaving racking turns (figure of eight) between the poles is a good alternative.
The basic approaches to tying a shear lashing vary in how tight to make the wraps and fraps. The poles have to pivot in order to spread out the desired distance. How can this be accomplished so the lashing is tight, but not so tight that when spreading the legs into position, the legs and lashing rope resist the strain to the point that something breaks? The tighter the wraps, and the more wrapping turns you take, the stiffer the lashing will be.
- One view is to make the wraps and fraps on the loose side, concluding they’ll tighten when the legs are spread.
- Another view is to place a small block of wood between the spars to yield adequate room for the frapping turns.
- Another view is to make the wraps moderately tight and then before frapping, spread the legs a bit to allow room for the frapping turns, being careful not to close the spars on the lasher’s fingers!
- Finally, another view is to complete the wraps, then spread the legs to the desired width, and then take tight frapping turns.
Whatever works well will also depend on the diameter of the spars, how straight they are, and indeed on the structure itself.