This is the first I've heard an inkling of a problem. We've been tying Dyneema for 30 years or so now haven't we? I concede that a loose bowline could come undone if it is not "set" correctly, but that is user error, and nothing to do with the the knot or the rope/line. Just set the knot correctly and keep it simple. I do like the idea of the Dog and Bone holding a spliced loop though, but can see also that it could shake itself loose.
Tying Dyneema sheet to spinnaker
- Thread starter jasonsansfleece
- Start date
The party lights in the back yard run along some chineema 1.8mm kite string to turnbuckles tied using bowline knots, no issues. Those wobble around in the wind rain and sun 24/7 365. I hate untying dyneema bowlines with smaller line though.
On larger boats we use soft shackles because you can train everyone on the boat, even the greenest rookie, how to use one in about 30 seconds and master them in 90 seconds, haven't had one shake loose yet. Stopper knot looped through some slack works fine too but some people struggle with "i can't tie knots, i can't tie this either" whereas "soft shackle = someone already tied the knot for me". These days you take any crew you can get.
"Reliable" has several definitions. Would I tie a bowline in dyneema for a spin sheet? Sure. Would I trust it to haul someone up the mast? No
On larger boats we use soft shackles because you can train everyone on the boat, even the greenest rookie, how to use one in about 30 seconds and master them in 90 seconds, haven't had one shake loose yet. Stopper knot looped through some slack works fine too but some people struggle with "i can't tie knots, i can't tie this either" whereas "soft shackle = someone already tied the knot for me". These days you take any crew you can get.
"Reliable" has several definitions. Would I tie a bowline in dyneema for a spin sheet? Sure. Would I trust it to haul someone up the mast? No
Tom O'Keefe
Super Anarchist
In the video on page one the presenter explains the problem with Dyneema is it has a low melt point. Under highloads the friction in a knot will melt the contact surface and cause an already slippery surface to become even more slick. That's when blowlines in dyneema fail.
The year we won Pac Cup, we had just such a failure in a spinnaker halyard. We saw the beginnings of chafe near the splice, cut it out and naively tied a bowline back in with a locking half hitch. At about 11:00 pm in a 30 knot gust that sucker let go and laid the 4A right out in front of the bow. I fortunately heated up and didn't run it over. But, that was our lesson. No knots in dyneema.
The year we won Pac Cup, we had just such a failure in a spinnaker halyard. We saw the beginnings of chafe near the splice, cut it out and naively tied a bowline back in with a locking half hitch. At about 11:00 pm in a 30 knot gust that sucker let go and laid the 4A right out in front of the bow. I fortunately heated up and didn't run it over. But, that was our lesson. No knots in dyneema.
overdraft
Anarchist
I think all the comments about knots slipping out of spectra/dyneema are very relevant if you begin to approach the limits of the line. For example 4mm Amsteel has an average strength of 1,800kg… but how much load is really on your kite sheet which will be sized for handling, then maybe elongation for some applications, and ultimate strength probably last… I’ve been tying spectra sheets to 24 foot sport boat asymmetrical kites with bowlines for some time with no issues.
jasonsansfleece
Member
- Thread starter
- #25
I haven’t really tied in knots in dyneema before, certainly not in a loaded and dynamic situation such as a spinnaker sheet, hence starting this thread.
Having read your replies, and tried a double bowline, especially with the tail brought around and passed under the loop at the top, a knot it will be. It’s simple (as long as everyone can tie it!) and inexpensive, both appealing.
Thanks, I learned something today,
Having read your replies, and tried a double bowline, especially with the tail brought around and passed under the loop at the top, a knot it will be. It’s simple (as long as everyone can tie it!) and inexpensive, both appealing.
Thanks, I learned something today,
What I do may be of interest. It is another use for what I called a soft Halyard Shackle HERE.
It is like a soft shackle but in two pieces. You make a small eye splice in the end of the dyneema sheet but stitch it back so you can open the eye like a soft shackle. Then you take a short section of dyneema and tie a button knot in it which is like a soft shackle without the eye splice. You cow hitch the piece with the button knot on the clew and then just open the eye on the sheet and put it over the button knot to attach the sheet to the clew. I use two of the button loops, one for each sheet but it depends on how you use your boat. This setup is incredibly strong. As a benchmark, if you used 1/8 inch dyneema and a 34 power winch, you could not pull hard enough to break it.
The problem with knots in Dyneema is that they slip at very low percentage of line strength. I can't remember exactly but it is something like 30-40% of line strength unless you get into the fancy knots in my video, linked above. Those knots are strong but you usually untie them with a knife. Once Dyneema starts to slip, it is all over . It is like falling over a cliff rather than falling down the slope of a hill. A friend watched a shipmate get killed when the dyneema slipped on a winch. As was said, it melts and at that point all its strength is gone instantly. In my testing, I saw flames when the Dyneema slipped.
It is like a soft shackle but in two pieces. You make a small eye splice in the end of the dyneema sheet but stitch it back so you can open the eye like a soft shackle. Then you take a short section of dyneema and tie a button knot in it which is like a soft shackle without the eye splice. You cow hitch the piece with the button knot on the clew and then just open the eye on the sheet and put it over the button knot to attach the sheet to the clew. I use two of the button loops, one for each sheet but it depends on how you use your boat. This setup is incredibly strong. As a benchmark, if you used 1/8 inch dyneema and a 34 power winch, you could not pull hard enough to break it.
The problem with knots in Dyneema is that they slip at very low percentage of line strength. I can't remember exactly but it is something like 30-40% of line strength unless you get into the fancy knots in my video, linked above. Those knots are strong but you usually untie them with a knife. Once Dyneema starts to slip, it is all over . It is like falling over a cliff rather than falling down the slope of a hill. A friend watched a shipmate get killed when the dyneema slipped on a winch. As was said, it melts and at that point all its strength is gone instantly. In my testing, I saw flames when the Dyneema slipped.
beercanned
Member
If you think tying knots in dyneema is easy, wait until you see how easy it is to splice!
Locus
locus
Just splice a soft shackle in the end self contained always the same length easy to undo if the chute gets f'd
It is a lot easier to undo what I posted above than a soft shackle spliced to the end of the sheet. Which brings me to the question, why do I have a soft shackle spliced to the end of my main halyard instead of what I posted? I think I shall change it.
jasonsansfleece
Member
- Thread starter
- #30
That’s another clever approach allene222 but what concerns me with soft shackles and their like is what happens to those diamond knots and opening cords when they get pulled through the jaws of a spinnaker pole? (Which is the application in the original post, and not to discount all the ingenious ways of connecting things with line)
Maybe they don’t and I imagine it depends on the size and orientation, not having it in my hand?
Maybe they don’t and I imagine it depends on the size and orientation, not having it in my hand?
That is a good point. My suggestion would be to use a large enough line for the part that gets connected to the clew so that the pole jaw cannot pass its larger diamond knot. There is nothing that says the line making up the diamond knot has to be the same size as the core of the sheet. You would just need an eye that could open enough to go over the larger knot. I might ask if you use a bowline, what is to keep the pole from getting stuck in that knot? The other thought that comes to mind is to use a shackle guard although as it would not be captured on the sheet, it might present some rigging challenges. The shackle guard just needs to be large enough to pass easily over the sheet splice but small enough to get hung up on the diamond knot. Full disclosure, I have only used this method myself on an asymmetric spinnaker and on a large free flying jib.
Locus
locus
Ball or doughnut in front solves the issue
Also I actually turned the end of the line into a shackle not a separate line.
Also I actually turned the end of the line into a shackle not a separate line.
I second the Splice and Soft Shackle with a ball to prevent jam and I'm a old timer. Where was Dynema and soft shackles when i grew up? Have a lot of scars from big shackles hitting me in the head. Put a tapered cover where the line goes thru the pole just like you should do with tapered halyards where they ride on the sheaves.
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Waynemarlow
Super Anarchist
Be aware guys & gals there are locking Brummell splices and non locking Brummell splices. Anything that is not of a constant tension such as Spinny lines will need a locking version.
If you are not sure then a few simple stitches through the tail of the taper will get you out of trouble until you can work out how to create a locking splice.
If you are not sure then a few simple stitches through the tail of the taper will get you out of trouble until you can work out how to create a locking splice.
Lock stitching is just as good as a brummell splice and a lot easier to remember. I have used both. Just run 8 stitches along the line and then turn it 90 degrees and run 8 more back to the beginning. In the picture above, I added a whipping over the lock stitches.
https://L-36.com/brummel2.php has instructions on how to do a brummell splice on just one end, which might be required if you are trying to put on in this stripped sheet. Otherwise you would need to pass the entire sheet through the stripped line. But I guess you could do that if you make a large enough opening.
https://L-36.com/brummel2.php has instructions on how to do a brummell splice on just one end, which might be required if you are trying to put on in this stripped sheet. Otherwise you would need to pass the entire sheet through the stripped line. But I guess you could do that if you make a large enough opening.
duncan (the other one)
Super Anarchist
knots slipping at 30% of breaking strength is hardly a problem on kite sheets unless you like working with line the size of knitting wool.
A skiff knot would probably do the job.
A skiff knot would probably do the job.
True. The question is can you get to that load if there is a big jerk on the line like the wind lets up, everything goes slack and then bang, a shock load. If it would just slip a little that would be fine but this stuff can turn to liquid and then any load will cause it to fail. I
I think you are basically correct as we have people here who have done it without failure. I wouldn't but that is just me. It is easier to use a line soft shackle than to tie a knot so why not?
I think you are basically correct as we have people here who have done it without failure. I wouldn't but that is just me. It is easier to use a line soft shackle than to tie a knot so why not?
SailingTips.Ca
Feigns Knowledge
Knots slipping in Dyneema isn’t nearly as bad as people think i.e. it’s much different than Dyneema slipping on a winch.
Here I test a soft shackle with an overhand knot with a hydraulic press:
Here I lift the front end of my car with the same kind of overhand knot soft shackle:
Here’s the integral soft shackle I use on my spinnaker, including break testing with a hydraulic press:
It’s not as strong as a splice and soft shackle, but still strong enough for a sport boat.
I’ve also used bowlines in Dyneema with no issues. My next experiment will be to lift my car with a bowline in Dyneema…
Here I test a soft shackle with an overhand knot with a hydraulic press:
Here I lift the front end of my car with the same kind of overhand knot soft shackle:
Here’s the integral soft shackle I use on my spinnaker, including break testing with a hydraulic press:
It’s not as strong as a splice and soft shackle, but still strong enough for a sport boat.
I’ve also used bowlines in Dyneema with no issues. My next experiment will be to lift my car with a bowline in Dyneema…
TradingUp
Anarchist
- 540
- 91
This.
I’m struck by the climbing world where verboten knots are given a name to provide perspective and mythology to the user.
European death knot anyone?
Spinnaker sheet today, bosuns chair tomorrow…
Nothing verboten about the European death knot,
It's one of the most common ways to tie rapel ropes together and is entirely fit for purpose.
For bosuns chair there is only one acceptable option in my opinion: climbers figure eight on unspliced covered line.
