Knotted string

[Hrothgar]

Pat, if this isn't the proper place to ask this question, please feel free to move it.

I've heard that anytime a string gets a knot in it the strength decreases by half. I was wondering how accurate this statement is. I have an old bow stringer which has accumulated several knots over the years and wonder if it is still safe to use, also a 'long string' for tillering purposes in a similar condition.

Any engineers, physicists, or enlightened individuals who could explain the dynamics involved here please chime in.

Thanks

[Pappy]

Never had a bow stringer that didn't get knots after it has been used for a while, don't know what but mine always do, never had a problem with one breaking.
 Pappy

[Pat B]

I wouldn't worry about a bow stringer with a few knots in it. A long string usually isn't under much stress so I wouldn't worry about a few knots in the long string either but I would not use a bow string with a knot in it.

[Lucasade]

The first knot decreases the strength by half - any further knots don't have an effect. Don't ask me to explain that statement, it is what I was taught in my working at height course.

[Jim Davis]

The first knot decreases the strength by half - any further knots don't have an effect. Don't ask me to explain that statement, it is what I was taught in my working at height course.

Correct. It's because the knots are of equal strength/weakness. It's like a weak link in a chain. If you have two equally weak links, the chain will break at the strength limit of one of them.

But bow stringers never have as much strain on them as a bow string.

[Onebowonder]

The stringer is only pulling the bow to - or just slightly beyond - brace point.  It is a very odd and rare bow holds anything like full draw weight tension at brace.  Your stringer should be fine in any case.

I would not mind if someone would be inclined to share why a knotted string is only half the strength.  My limited little pea brain is not able to contrive a reason that such would be the case.  I can imagineer a few excuses for the string to perhaps be a bit less strong, but why would it be 'half'?  Also, what is a knot?  There are any number of knots possible.  Do they all subtract an arbitrary half of the strength of any given string?

OneBow

[PEARL DRUMS]

Might make sense with single strand small diameter cordage that are able to cut themselves within the knot. I doubt the number is that high with a 10 strand reverse twist FF string, I would wager strength loss to be more like 5-10% in that scenario.

[burchett.donald]

 A continuous loop string allows some slippage of each strand to even themselves out in tension during use...I think when a knot is introduced it can cause uneven tension on each strand which can cause problems...You can't put a percentage on the strength, to many variables...May break on the first shot or it may never break...I just couldn't continue shooting if I knew a knot was there...JMO
                                                                                                                                       Don

[DC]

I would be willing to bet that the "half" is an engineers rule of thumb. Kind of a worst case scenario to cover their butts

[PatM]

 The most powerful bows made had knotted strings.

[JoJoDapyro]

Isn't a bow under the most stress while at brace?

[Jim Davis]

Lots of interesting thoughts here, but the OP was considering a bow stringer, not a bow string.

[loon]

The most powerful bows made had knotted strings.

Hornbows or English bows? Do you have any details? Apparently some heavier Tatar bows had essentially flemish ramie strings with double loops.

[Chief RID]

Only thoughts I have had were knots tied in terminal tackle for fishing. Different knots have different strength and provide different action for lures or better weedless qualities or other stuff. I guess it is how the knot distributes the pull of the parts of the knot that makes some knots better than others.

[burchett.donald]

Asharrow,
                  He mentioned a string, a bow stringer and a tillering string, so we are all on topic sir...
                                                                                                                                                  Don