Bent Sheep and Bo Derek

[NigeCh]

Lay a classic bowline and then twist the tail part round the standing part of the made loop under the standing part and you will get a stronger knot that won't jam.

The reduction in strength is purely due to the radius of bend on the standing part which if tensioned to extremis will break within the knot: ie a classic rabbits and tree trunk bowline. Twist the tail under the standing part of the made loop and a) it won't fail within the knot and b) will be unjammable (try it with Dyneema rope) ... ie it becomes a side-laid bowline. The two knots are entirely different.

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[peterb]

Broken bowlines

Yes, it usually broke just where the standing part entered the knot.

A little thought explains it. Below the knot the two sides of the loop share the load. Above the knot the load is taken by one line only, so this is where it is likely to break.

But if you tie a bowline and look closely at the lines, you'll see that the line bends through about 30 degrees where the standing part enters the knot. That means that, before there is any load, the fibres on the outside of the bend are slightly stretched and the fibres on the inside are compressed. As the load increases the outer fibres will always carry a greater load, and so it is here that the break begins.

The extent to which the fibres can share the load depends on their elasticity. If you imagine a material that had no stretch at all, then the fibres on the inside of the bend would be slack and unable to take any of the load. Since the outer fibres would then be carrying all the load the loss of strength would be high and fracture would be early. On the other hand, if the fibres are elastic then the outer fibres can stretch to allow some of the load to be taken by the inner ones. On this basis the loss of strength depends mainly on the radius of the bend. That's why the sheaves used in blocks for materials like Kevlar need to be of greater radius than those for polyester or nylon.

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