Shear Lashing

Building an A-frame shelter support, a simple two-legged trestle, or the start of a tripod all share a common need: two poles lashed together at one point that then spread apart at the other end, working as a hinge rather than staying locked at a fixed angle the way a square-lashed joint does. The shear lashing achieves exactly that by deliberately tying its wraps looser between the two poles than a square lashing would, leaving enough play for the poles to pivot open into the spread shape once the lashing is complete.

The technique wraps the cord loosely around both poles held together, then adds a modest set of frapping turns - enough to gather the wraps neatly and keep them from sliding, but not cinched anywhere near as tight as a square lashing's frapping stage, since over-tightening here would lock the poles rigid and defeat the hinge action the lashing is meant to provide.

Getting that tension right takes some judgment: too loose and the lashing itself can slip or the poles can wobble excessively at the hinge point; too tight and the poles simply won't spread into the A-frame or tripod-leg shape needed. Most builders test the spread by hand partway through tying, before the final frapping turns are locked in, to confirm the hinge moves freely enough.

A shear lashing on two poles is also the direct foundation for a tripod lashing on three - the same loose-wrap, modest-frap principle extended to a third pole, which is why anyone who's mastered the two-pole shear lashing finds the tripod version a fairly small additional step.

Beyond A-frames and trestles, shear lashing sees regular use rigging a simple lifting gin - two poles lashed near their tops and spread into an inverted V, with a pulley or rope run over the lashed point to hoist a load below. That's a genuinely different application from a static shelter frame, since the lashing itself takes real, ongoing working load from whatever's being hoisted rather than simply holding a fixed structural shape, which makes getting the tension right - secure enough to trust with a hoisted load, loose enough to have formed the hinge properly in the first place - even more important than in a purely static A-frame.

The rope or cord chosen for a shear lashing intended to bear real hoisting load should be meaningfully more robust than what's adequate for a simple static camp trestle, since the lashing here is doing double duty as both the hinge mechanism and part of the actual load path during a lift.