A knot that drives you around the bend!
On a cave excursion through Bulmer cave system (New Zealand) I noticed, on two occasions, a single sheet bend rigged at the top of a fixed handline but being used as if it was a bowline knot. I suspect the person rigging these handlines meant to tie a bowline knot but got it wrong.
The way to tell at a glance if you have a sheet bend is the bight is on the inside of the loop formed compared with the outside for a bowline.
Under the general classification of ‘knots’ there are three subsets namely knots, bends, and hitches:
Where a connection is tied that is self-sustaining in rope or webbing. If the knot was tied around an object, and the object is removed, the knot remains intact, for example, the bowline knot. “If it’s not a bend or a hitch then it’s a knot”.
Where two pieces of rope or webbing are tied together usually at their ends, with both playing an integral part. The load is pulling in line through the bend, for example, the double fisherman’s bend.
Where a rope is tied to an object where if the object is removed the hitch falls apart, for example, the clove hitch.
We completed two tests (testing Prattley and Mandeno, July 2005) of the single sheet bend pulled as a knot, gradually increasing the load with a 10-ton jack. We used older ropes represent typical handline material found in caves.
The first test was with a 7-year-old 8mm length of Mammut accessory cord. The bend inverted when pulled then slid and cinched against the testing carabiner. The knot inverted at around 3kN and once cinched against the carabiner locked tight until the rope broke at 7kN.
8mm Mammut accessory cord
The second test was with an 8-year-old 10mm length polyester Donaghys cave rope. The bend inverted when pulled, slid and cinched against the testing carabiner. The knot inverted at around 4kN and once cinched against the carabiner locked tight. The load was taken up to 12kN without failure.
10mm Donaghy polyester rope
Conclusions and thoughts
- Pulled as a knot the sheet bend performs poorly as it inverts and slips.
- We only did two tests. It gave us an indication of the type of failure.
- It is important for you to recognise what is a knot, bend or hitch and use them appropriately.
- If you cannot recognise the difference between a sheet bend and bowline knot, use a rethreaded figure-8 for handline rigging.
- Make a check of fixed handline rigging before using. Just because it’s there doesn’t mean it’s safe.
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