knots; how do they affect strength of cordage?

[Pootle]

Is it just the portion of the rope that makes up the knot that is weakened?
I'm trying to get my head around how multiple knots affect strength.
I'm thinking that the overall strength would be that of the 'weakest knot' If you get my meaning?
any Info gratefully received!

[OakAshandThorn]

A lot depends on the type of knot. An overhand knot tied into the middle of a cord (accidentally through tangling or otherwise) will reduce the cord's strength significantly, and that should be avoided at all costs, because it will also be a pain in the you-know-what to undo if the cord was put under a lot of tension. But knots like the clove hitch, constrictor, alpine butterfly, lark's head/cow hitch, Prusik, and the various figure 8s have a minimal effect. Both the clove and constrictor are particularly good if the cordage is natural fibre.

I believe that in mountain rescue and SAR (please confirm, Sapper ), stopper knots are frequently tied as a way of stopping another knot from coming undone, such as putting in a double overhand at the tag end of a bowline. Double overhands are reliable stopper knots and provide more of a toggle effect than a figure 8 would.
Some folks like myself tie a bunch of double overhands in the webbing of our hammocks every 30 cm or so, that way our setup is quicker and easily adjustable. And that brings into mind the overall strength of the cordage minus any knots, which is also an important factor. Because this webbing is usually heavy duty climbing-rated, you don't really have to worry so much about knots compromising the strength.

[tds123]

A knot is always the weakest point, that's why its always best to splice rope whenever possible.

[Pootle]

Sorry gents, I only just found your replies.

OAT, you mentioned regularly spaced double overhands for hammock adjustments...that's exactly what got me asking in the first place.
I was wondering, If I tied a series of knots, would each one reduce the strength by a further 50% (for example) or would it just be reduced once?
I guess if you've been doing it without hitting the deck then it must be the latter?

[OakAshandThorn]

Sorry gents, I only just found your replies.

OAT, you mentioned regularly spaced double overhands for hammock adjustments...that's exactly what got me asking in the first place.
I was wondering, If I tied a series of knots, would each one reduce the strength by a further 50% (for example) or would it just be reduced once?
I guess if you've been doing it without hitting the deck then it must be the latter?

If they're double overhands, it shouldn't do anything major. Double Figure 8s would be even better. I've done double overhands in my hammock setup, no issue whatsoever...then again, I'm fairly light at 9 stone. But if you use climbing grade rope/webbing, you should be totally fine .

[Ashley Cawley]

Pootle I'm sure you'll be fine if you are using webbing that was issued with a hammock already, I've tied a variety of knots into hammock webbing and have never given it a second thought as I don't believe it'll significantly weaken it to the point it will break. Obviously if your experimenting with some other cordage that was issued with the hammock then that might be a different matter, in that case find a friend who is slightly heavier than yourself and invite them to "try out your new hammock setup" then observe for any failures

[Pootle]

Cheers gents, it's the cordage that came with it, a tw hammock. I'll give it a try and see how I get on.
Ashley, I'll definitely borrow someone else's weight for the test run!😈.

[shack]

The good old www. Should give you all the info you need, each knot does reduce the breaking strain and therefore safe working load of a rope/ cordage by differing amounts.
Many years ago I trained as a tree surgeon and I'm sure we had a fun afternoon looking at some of these statistics. With the development of kevlar cordage and the silly strenghs these have it will be interesting to see how things develop, we used chunky multiplait hawsers Im sure.

[Durham Bushcrafter]

Knot strength refers to how a knot weakens the breaking strength of the line. The twists, loops, and turns of a knot place unequal stress on the line that reduces the lines breaking strength by about 50% (Jacobson 1999). Lines of different materials, weaves, and diameters will have different characteristics and strengths.

[midas]

Hi Durham Bushcrafter,welcome to the forum.
There is an introduce yourself n welcome to the forum,listed in "Off Topic.go to forum ,scroll down n you'll see it.
then all the members can welcome you on board.and find out your interest,.atb .mike