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> Some knots are 100% safe
Perhaps, but
"It should be borne in mind that a knot weakens a rope at any time." -- Burgess, J. T. (1828-1886).
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All knots reduce the breaking strength of rope. The question is, has been, and will always be, how much? The general rule has been a knot reduces strength approximately 50%. That is almost true.
In early 2004 I asked and received permission from the Cordage Institute Technical Committee to conduct a study on knot efficiency. The Institute solicited donors of many types of ropes to be tested.
A Butterfly knot had the highest efficiency in the 10.5mm at over 80%. The Double Fisherman's Knot seemed to be the best joining knot. Most all of the joining knots required backup knots.
The most efficient end line knots Butterfly and Figure 8 knots have a disadvantage of being almost impossible to untie after a significant load of about 1,000 lbs. was applied.
The standard Bowline was selected for the test, but the Cowboy or Dutch Bowline was tested to see if there was a difference. The numbers were almost identical.
Dave Richards, Technical Director, Cordage Institute
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