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In researching knots for tying onto an eye, I found one that loops the string through the eye then through it a second time. Does this improve strength? Spreading out the load somehow?
depending on the structure of the knot it is likely spreading the load across twice the string, therefore halving the load on each. This only adds value if the whole knot is doubled, or if the contact with the eye would otherwise be a stress point.
The doubling could also be to prevent rotation on the eye as it will introduce friction at the point of contact. Not sure why this would be necessary but knots can be quite niche.
Could this be the round turn and two half hitches? It is a great strong knot, but not the very strongest if that is what you are after. (which I doubt). The strength of a knot is determined by how much it reduces the breaking strain of a line, usually expressed as a percentage. The strongest commonly used knot is a bowline .
The main characteristic of the round turn and two half hitches is that it can be untied when under load, not something you can achieve with a bowline.
Mechanically, the round turn does the work, providing friction to stop the force from the load on the line jamming up the knot and making it hard to undo. The half hitches above just hold everything in place , saving you the trouble of standing there holding the round turn in place for ever!
What are to tying it too?
I know a bit about knots, but here’s a good little guide.
The strongest commonly used knot is a bowline .
That depends on the material you are tying it with. Knots used in fishing with nylon monofilament are different to those used in sailing, and different to fishing knots for braid. Climbers favour different knots again.
Anyhoo two turns will increase the friction and halve the wear, should that be relevant.
Ah yes, fair one. Hadn't thought about monofilament.
OP-Fisherman's bend if its monofilament.
[i]lesshaste wrote:[/i]
Could this be the round turn and two half hitches? It is a great strong knot, but not the very strongest if that is what you are after. (which I doubt).
It's the standard knot for tying a line onto something fixed though and the first thing which came to mind for the OP's requirement. I have to admit I don't know much about the characteristics of various knots, though as you suggest it's unlikely ultimate strength is an issue - but to answer the original question, yes the doubling would spread the load.
BTW I'm not sure what your definition of "commonly used" is - I'd be very surprised if a bowline is stronger than other knots typically used in climbing such as a retied figure 8, but then I wouldn't normally use either for tying onto an eye.
edit: I've used round turn and two halves on monofilament and it works fine, though I tend to do a double round turn (ie 4 wraps) or more to increase the friction when doing that!
Yes, sorry. My knowledge is biased towards sea going activities and not very up to date. Don't know much about dangling off rock faces.
I thought a round turn and two half hitches was supposed to be stronger than a bowline?
The advantage of a bowline is it pulls itself tight so won't undo, great for attaching halyards to sails etc.
The advantage of a round turn and two half hitches is the straight run of rope into the round turn makes it very strong but the half hitches are easy to undo even under load (because the round turn does all the work), good for mooring lines, not so good for anything permanent.
If its something permanent though it should be spliced. Splices are near 100% efficient if done well.
It was this one:
Who knows about knots?
I'm afraid not.
The strange thing then is that I think a double fisherman's is also stronger (I have a feeling it might be close to the ultimate strongest) - is that not a nautical knot given the name (I note it doesn't appear in bikebouy's pic either)? I guess that's originally a monofilament knot!
Splices are near 100% efficient if done well.
Last time I did one it was crap 😛
[i]molgrips wrote:[/i]
It was this one:
That's (k)not a round turn and two halves - interesting, I'm not sure I've seen that specific knot before, it's kind of a combo of the round turn (presumably the double wrap for reasons already explained) and a hangman's noose (could also be described as a multi fisherman's knot). Kind of like https://en.wikipedia.org/wiki/Uni_knot but with a double turn, and given the similarity to a double or triple fisherman's I'm not surprised to see it work well on that sort of cord.
The strange thing then is that I think a double fisherman’s is also stronger (I have a feeling it might be close to the ultimate strongest)
I think a double figure of 8 is still stronger on rope at least.
It depends on a lot of factors though, if you're attaching to an eye then the rope will probably snap where it goes round the eye regardless of the knot. That's why there's a difference between a chain splice and an eye splice in bikebouys diagram, the eyesplice is designed to go round something big (or have a metal eye incorporated in the splice) whereas the chain splice splits apart the strands to effectively reduce the ropes diameter where it goes round the smaller diameter chain.
It depends on a lot of factors though, if you’re attaching to an eye then the rope will probably snap where it goes round the eye regardless of the knot.
That's why I'm wondering if the double loop is significant here - if it increases strength.
The bowline isn't that strong as it reduces the strength of a rope by around 50%. The fisherman's knot is quoted about 70% (30% reduction in strength) from memory.
I'm not sure what you mean by strength. Very few knots (or bends) significantly weaken the rope. So if you are getting close to breaking strain you'd better do something else.
The vast array of types are mainly down to slipping, different types of rope, the joining of ropes/cords of different thicknesses and/or materials, and ease of untying.
If you specify what you're doing and using I'm sure Bikebouy will point out the right sort. I'm just a windsurfer so we only use 2 sorts, neither of which has an official name, they're just artless bodges.
There's some charts on this page about knots and bends. Bowline and Fo8 are in the mid 60% to 70% of unknotted rope strength range. With modern ropes this is more than adequate regarding absolute strength. When climbing the ropes used are "dynamic" and stretch quite substantially when a load is applied. In a fall this reduces the impact force by spreading the load over time which means that the climber doesn't come to a sudden stop and experience very high deceleration.
The big advantage of the Bowline over the Fo8 is that it's easy to untie after a load has been applied. This also means that unless the Bowline is properly set and has a stopper knot then it's possible for it to come undone. Not good in a climbing situation! In over thirty years of climbing I always used a Bowline in preference to a Fo8 and never had one come undone but it's one reason why climbing walls insist on people using Fo8 knots.
There are several reasons to choose one knot over another, strength is just one of them.
It also depends on what type of rope - traditional spun ropes work better with bowlines, bends where the twist in the rope helps pull it tight. Sheathed / kernel ropes work better with figure-8s and stopper-knots. Spent some time crewing on traditional sailing boats and putting the wrong knot can create problems e.g. working loose or not wanting it to come undone and we'd always have to drill crewmembers to get it right e.g. sailing in rough seas at night and you're up aloft trying to deal with someone's bastard-hitch whilst hanging on with one hand! The strength is still down to the diameter of the rope, the knot is simply to stop it from coming undone. A full-loop around an eye will help spread the load, plus you have the friction created by the loop 'binding' against itself
[i]whitestone wrote:[/i]
There’s some charts on this page about knots and bends.
Interesting - so I was kind of right about the double fishermans, though interesting to see the butterfly on top in some cases. As you suggest, ultimate strength is largely irrelevant most of the time, but it's not something I'd particularly have thought of using for anything other than tying into the middle of a rope.
The big advantage of the Bowline over the Fo8 is that it’s easy to untie after a load has been applied. This also means that unless the Bowline is properly set and has a stopper knot then it’s possible for it to come undone. Not good in a climbing situation! In over thirty years of climbing I always used a Bowline in preference to a Fo8 and never had one come undone but it’s one reason why climbing walls insist on people using Fo8 knots.
I had thought of mentioning that, but thought it would confuse things - I also use a bowline to tie in because it saves me about 5 minutes after taking a big lead fall! I use a Yosemite finish (which does of course introduce its own issues of being so easy to set wrong) and a stopper knot, so fairly confident it won't come undone - quite a few of the better climbers I climb with also use bowlines. The local climbing wall seem happy enough with us using them, but then we're on first name terms with all the staff and they trust us to know what we're doing - though I only use one on lead, haven't ever tested them by tying into a top rope with one!
Ah, my day job is the design of ropes, so yes, I do know something about knots.
I'm in the very privileged position of having a tensile test machine outside my office door so when someone says "how strong is X knot in Y rope?" I can actually go and find out rather than google it.
After doing this for too many years I've learned a few things:
- Splice ropes if you can.
- Knots are not consistent, what works well in one rope is less good in another. Sometimes even the way it's tied can make a difference.
- As a general rule knots with larger D:d ratios are better. (D:d being the ratio of the diameter of the rope to the diameter it's being bent around.) This means that despite common wisdom, a fig 8 is normally stronger than a Bowline as the rope is doubled throughout the knot.
- Knots are more efficent in materials that have high elongation. The flip side of this is that knots in high performance materials like Dyneema, Vectran, Technora, Kevlar, etc are all a bit rubbish.
- As a general rule in polyester/nylon type ropes assume you'll lose 50% of the strength. In high performance ropes assume 60+% loss.
-Some knots, like the round turn and 2 half hitches mentioned are dependent on the diameter they are being tied around so do actually have the potential the be very efficient but not in every case.
Personally, I'd just learn a few knots that you can tie reliably under any circumstances and not worry too much. I reckon you can do most things with rope with a dozen knots.
@Harry Tuttle, nice post. Always amazed at the breadth of actual knowledge on here. I know about ten knots and haven't yet found a situation that I can't bodge something with these. However, as mentioned above, I don't climb stuff. I think the one that is less commonly used but is really useful and versatile is the rolling hitch.
Knots are more efficent in materials that have high elongation. The flip side of this is that knots in high performance materials like Dyneema, Vectran, Technora, Kevlar, etc are all a bit rubbish.
Fascinating.
The setup is that I have been trying for a while to replace the PAR cable in my Marzocchi forks*. Originally I twisted my own yarn out of bow string and rather than knot it I re-wove the thread back into the twist of the yarn. Then I wrapped it with some thin string. This worked pretty well but the string was too short and in the end it started to fray. I tried repeating this but both times I got the re-weaving part wrong so it wasn't strong enough.
So I ordered kevlar braided line from eBay. It was meant to have a 300lb breaking strain but I tied a palomar knot in each end of a section and I was able to snap it using a deadlift action. And I can't deadlift 300lbs 🙂 May have been due in part to using allen keys to pull it.
The knot in the vid seems to be a good bet because the string goes straight through the winding bit and hence pulls directly on the pin. Seems to have survived a ride.
* Looks like this:
