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Relative knot strengths
- Thread starter mikem
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Cantclimbtom
Well-known member
I 90% agree with Josh, that rope snapping in the knot isn't a likely failure scenario unless many other things are already catastrophically wrong in which case the knot wasn't your problem. So the strength of common knots isn't often very relevant.
That all said.. I been wrong and surprised by counterintuitive stuff. For example joining two ropes by just trying a fig 8 in the two ends (not sure I'd have done that rather than a double fisherman's or a rethreaded 8?) is dangerous and can roll undone, whereas the scary looking overhand "European Death Knot" / "EDK" (https://en.m.wikipedia.org/wiki/Offset_overhand_bend) is far safer and much less likely to get snagged on rock when retrieving. Now I'd never have expected that
Or.. when using dyneema/spectra/etc materials for cords, a double fisherman's knot is absolutely unsafe (can slide and roll undone at amazingly low loads, like 1kn in some cases) whereas for a normal rope or cord it's an ideal choice
So a bit of education can be useful on knots (thanks MikeM) but I'm not earning some scout badge or something to be a knot nerd to memorise percentages, but sometimes there are unintuitive things and we can all benefit from learning
That all said.. I been wrong and surprised by counterintuitive stuff. For example joining two ropes by just trying a fig 8 in the two ends (not sure I'd have done that rather than a double fisherman's or a rethreaded 8?) is dangerous and can roll undone, whereas the scary looking overhand "European Death Knot" / "EDK" (https://en.m.wikipedia.org/wiki/Offset_overhand_bend) is far safer and much less likely to get snagged on rock when retrieving. Now I'd never have expected that
Or.. when using dyneema/spectra/etc materials for cords, a double fisherman's knot is absolutely unsafe (can slide and roll undone at amazingly low loads, like 1kn in some cases) whereas for a normal rope or cord it's an ideal choice
So a bit of education can be useful on knots (thanks MikeM) but I'm not earning some scout badge or something to be a knot nerd to memorise percentages, but sometimes there are unintuitive things and we can all benefit from learning
traff
Member
Interesting video, but presumably some of the samples ended up on the cutting room floor as the numbers presented don't add up with what was shown. One of the badly dressed ropes tested stonger than a good one and the other was close. I'm sure there has been more testing elsewhere but those numbers and apparent sample size don't convince me it's important.
However IMO a correctly dressed knot is typically easier to undo but more importantly you can tell it has been tied correctly.
However IMO a correctly dressed knot is typically easier to undo but more importantly you can tell it has been tied correctly.
Loki
Well-known member
That what average means. Some results are higher and some lower. Taken from a reasonable sample size.
It's almost impossible to tie knots to the same tightness for consistent comparable results. Interestingly a previous test showed overhand loop was stronger with load rope around outside of knot, figure 8 didn't really matter, but fig 9 was stronger with load rope on inside of bend - all of them were far stronger than our bodies would endure
traff
Member
I know perfectly well what average means (no pun intended), I didn't waste all that time at school, uni and 25 years as a control systems engineer for nothing.. I'm pointing out the samples shown in the video do not give the results they presented. The sample size demonstrated is far to small to ratify the conclusion they made.
JoshW
Well-known member
This and it also reduces risk of things (typically digits) getting caught in knots as they go under load.
I bang on about tidy knots at work all the time because I’m boring.
Loki
Well-known member
They probably didn’t want to bore the audience by showing everyone all the tests. See one knot bust and you’ve seen them all bust. Pretty dull viewing. I’d rather see drop test outtakes where it all goes pear shaped.
Mark Wright
Well-known member
As Loki says, it would be a pretty boring video if they had shown every knot they tested. I think we all got the gist of it. I thought it was pretty well produced, though with my son as the producer and resident knot tyer, I would say that.
It's been well known within the rope access industry for decades that poorly tied knots are weaker than correctly tied ones. I seem to remember a Bowline with the Rabbit going back down the hole on the outside is about 10% weaker than if it went down the inside of the hole?
If you tie knots in new ropes every day of the week as part of your job you can be pretty consistent with the force required to properly set the knot once dressed. Most of the industrial knot testing for standards purposes is carried out after a specified pre-load, e.g., 50kg or 150kg. It's a long time ago but I think Lyon Equipment used to pre-load their Fig. 8 terminated ropes before applying a protective shrink sleeve over the knot.
There's nothing boring about tying knots properly. I've been banging on about the importance of it in industry for nearly 40 years.
The late Clifford Warren Ashley wrote:
'A knot...is either exactly right or it is hopelessly wrong'.
Come along to the SRT Race stand at Hidden Earth this weekend and you can test your knot tying skills on some of Spanset's new rope. Get some practice in though as its behind your back and you get a 5 second penalty for every dressing fault. Fig. 8 & 9 on the bight, Bunny, Alpine Butterfly and a Double Fisherman's in a 2m length of rope.
See you there.
It's been well known within the rope access industry for decades that poorly tied knots are weaker than correctly tied ones. I seem to remember a Bowline with the Rabbit going back down the hole on the outside is about 10% weaker than if it went down the inside of the hole?
If you tie knots in new ropes every day of the week as part of your job you can be pretty consistent with the force required to properly set the knot once dressed. Most of the industrial knot testing for standards purposes is carried out after a specified pre-load, e.g., 50kg or 150kg. It's a long time ago but I think Lyon Equipment used to pre-load their Fig. 8 terminated ropes before applying a protective shrink sleeve over the knot.
There's nothing boring about tying knots properly. I've been banging on about the importance of it in industry for nearly 40 years.
The late Clifford Warren Ashley wrote:
'A knot...is either exactly right or it is hopelessly wrong'.
Come along to the SRT Race stand at Hidden Earth this weekend and you can test your knot tying skills on some of Spanset's new rope. Get some practice in though as its behind your back and you get a 5 second penalty for every dressing fault. Fig. 8 & 9 on the bight, Bunny, Alpine Butterfly and a Double Fisherman's in a 2m length of rope.
See you there.
Cantclimbtom
Well-known member
I'm interpreting "poorly tied knots" to include correctly tied but badly dressed knots.
I do dress knots due to my weird OCDs, and a well dressed knot is easier for others to inspect so there's arguments for dressing well.
I acknowledge exceptions of things that just don't work unless correctly dressed, Blake's hitch is an extreme (but obscure in caving/access) example, but fig8 bunny, alpine butterfly, etc, I still don't understand where evidence exists that poorly dressed common knots (e.g. fig 8) are significantly weaker. Also take fig9 (used to be an everyday rigging knot in access, back in the day) looks hideous however you try to dress it, why bother.
I don't get why people get so dogmatic about this topic, does it actually matter for most common knots... Why does it matter? (That's a genuine open question)
Happy to be persuaded/corrected otherwise if there's evidence.
Babyhagrid
Well-known member
I'm sure the risk of people getting cold behind you whilst rigging is much higher than the risk of a "badly" dressed knot snapping
Cantclimbtom
Well-known member
If you want pure speed, once you practice... you can tie a clove hitch one handed so fast and clip it to an open krab on a bolt in your other hand it looks like you are flapping your hand and magically the rope is clove hitched to a krab, 2 seconds to adjust the slack and you've moved on to the next one! Magic trick
JoshW
Well-known member
I mean that’s just a practice thing, you should be able to rig tidy knots as quick as untidy ones if you acknowledge that it needs doing
Mark Wright
Well-known member
As Clifford Ashley said, 'it's either exactly right or it is hopelessly wrong'. If it's badly dressed, then it isn't correctly tied.
Being able to easily identify and examine them, almost at a glance, should be a sufficient enough argument for tying them properly.
I'm not sure where the significantly weaker came from. I think the +/- 10% strength loss mentioned earlier is about the most a poorly tied knot will weaken it, as far as I know. Access Ace was suggesting only about 2.5% strength loss for Fig. 8's on their 10.5mm Spanset Gold rope. Even if there was a 50% strength loss they are still plenty strong enough.
I always used to use Fig. 9's and Alpine Butterfly's when making large 'Y' hangs at work and never had any problems dressing them neatly. The main reason I used them was because they're a bit easier to untie after loading. I was just talking to my son and he confirmed they did quite a few tests. Another interesting test he said they did, though admittedly not very scientific, showed that it took the testing team slightly longer to untie a poorly tied Fig. 8 that was pre-loaded with 100kg.
If you're not bothered about tying knots properly then it really doesn't matter at all, nothing is going to break. If you are teaching people how to tie knots though, then it makes sense to teach them how to do it properly and let them decide if they can be bothered dressing them. It shouldn't take any longer to tie a knot properly.
