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Amsteel and knots
- Thread starter noxninja
- Start date
I've seen even down to 1/3 of the original breaking strength.
Yep. You can literally splice it with just your fingers. Not necessarily pretty that way, but it's doable. I whipped up a rope to tie off my Grumman canoe with a locked brummel on each end in about 10 minutes while standing at my tailgate.
Ultimately what allows a knot to hold is friction. The trouble with Amsteel and similar fibers is they have a very low friction coefficient so knots tend to slip. When knots slip, apart from the risk of untying itself, there's a ton of friction and heat build up in a fiber that's not very abrasion resistant to begin with that causes problems. Low stretch fibers also loose a lot of strength around tight bends because the fibers can't stretch to equalize the load as much across the cross section of the rope so the inner fibers of the bend take a disproportionately higher percentage of the load further weakening the rope. Those factors and others, combine to give Amsteel poor knot strength. Cordage like that is designed to be used in "ideal" loading scenarios, i.e. spliced connections, straight pulls, minimal abrasion, large bend radius, etc., where the high strength advantage is maximized and the weaknesses are minimized.
The same physics effect conventional ropes too but the effects aren't as pronounced making them better suited to being used with knots. It's easy to get fixated on the high strength numbers of Amsteel but there's more to the story in real world applications.