Knots in Dyneema?

[Ohlin Karcher]

Having looked on Youtube etc, it seems dyneema is too slippery to tie knots in.
I have successfully tied knots in 3mm dyneema for lashings etc, but this is 12mm.

I bought 20m of new 12mm dyneema, sheathed, to make up a bomb-proof non-stretch preventer for my dangerously heavy boom, basically to categorically prevent gybes when deep-reaching in light airs while a swell is running, and I'm off watch.
Previously, polyester line has been uncomfortably stretchy in this role.. it runs from the boom end, outside everything, round a block near the stemhead, then back aft again. So quite long.

I ordered it with spliced soft loops but it arrived just hot-knifed, and no time to do it before I fly to the boat.

So I have to work something out.. I have never spliced this stuff and don't have the special fids, (no chandlers where she's berthed) but it needs attaching. Can anyone please suggest knots.. to attach to a big snap shackle or just to make a big soft- loop?
The material feels oddly hard and rigid..and very slippery! Just what you don't need for knots!
Someone must have been in a similar pickle? What did you do ?
Can it be sewn through, to make a loop?
Thanks in advance..

 

[AngusMcDoon]

Stitch & whip. Easy to do. Lasts years. Strong.

 

[Ohlin Karcher]

Stitch & whip. Easy to do. Lasts years. Strong.

Thank you sir.. that's how I make softeyes in old polyester lines.. it's good to hear the technique works in new dyneema as well.

 

[GHA]

Splicing is simple, a stubby pencil will do it. PCV tape the end of the line to the pencil then just feed the pencil down inside the main part of the dyneema. Then sort of go further than you need and pull it out the side then taper the end then pull it back inside the main part. Harder to describe than do
Quite a few people do a modified brummel splice scared that it might shake loose but a couple of lock stitches will help sleep at night if you're worried, straight bury splice with 50 x the diameter buried is up near 100% of rope strength. . Though with little help from google a modified brummel is pretty easy if you have access to both ends, tiny bit less strong but something else will break first.
Knots tend to slowly slip through under load, splice is the way to go.

Brummel looks like this, then feed the tail down inside the working part. Job done

http://atlanticbraids.com/dyneema-brummel-eye-splice-1-end/

 

[Ohlin Karcher]

Splicing is simple, a stubby pencil will do it. PCV tape the end of the line to the pencil then just feed the pencil down inside the main part of the dyneema. Then sort of go further than you need and pull it out the side then taper the end then pull it back inside the main part. Harder to describe than do
Quite a few people do a modified brummel splice scared that it might shake loose but a couple of lock stitches will help sleep at night if you're worried, straight bury splice with 50 x the diameter buried is up near 100% of rope strength. . Though with little help from google a modified brummel is pretty easy if you have access to both ends, tiny bit less strong but something else will break first.
Knots tend to slowly slip through under load, splice is the way to go.

Brummel looks like this, then feed the tail down inside the working part. Job done

http://atlanticbraids.com/dyneema-brummel-eye-splice-1-end/

That's excellent thanks a lot!

 

[[3889]]

A cow hitch apparently retains the same strength as a splice in dyneema. Curtail slippage with an overhand knot in the running end. This was my solution to a 'temporary' strop in the kicking strap 5 years ago and still going strong.

 

[GHA]

Some load testing >

https://web.archive.org/web/20160318230212/http://www.bethandevans.com/load.htm

 

[Ohlin Karcher]

Thanks to both of you, I'm looking forward to the job now!

 

[RobF]

I'm not sure about the cow hitch as a solution, although dyneema is so strong that I agree it's likely that something else will break first. Having just re-read my Yachting Monthly article on this very topic, they recommend the scaffold knot for dyneema. Your favourite search engine will reveal all.

 

[thinwater]

I've done a lot of testing of sewn eyes, some of it for publication. I'm a fan of the method, done correctly, for used polyester. But Nylon and Dyneema present special problems and are very difficult to do properly. I would not.

For get knots. A string of half hitches works on a lashing, but that's about it. As for line, they either slip (nearly all) or weaken the line MORE than polyester or nylon.

Learn to splice the single braid core. It's easy and all you need for 12mm is a length of rigging wire.

Although a Brummel lock is a cool trick, there is no need. So long as the tail bury is long enough, tapered, and the eye is lock stitched per the instructions, the strength is the same. But try the Brummel; it's worth learning.

http://sail-delmarva.blogspot.com/2016/11/rev.html

 

[greeny]

Having looked on Youtube etc, it seems dyneema is too slippery to tie knots in.
I have successfully tied knots in 3mm dyneema for lashings etc, but this is 12mm.

I bought 20m of new 12mm dyneema, sheathed, to make up a bomb-proof non-stretch preventer for my dangerously heavy boom, basically to categorically prevent gybes when deep-reaching in light airs while a swell is running, and I'm off watch.
Previously, polyester line has been uncomfortably stretchy in this role.. it runs from the boom end, outside everything, round a block near the stemhead, then back aft again. So quite long.


Not sure what "uncomfortably stretchy" means but surely a bit of stretch will give a bit of shock load absorption. Dyneema will not.

 

[Ohlin Karcher]

Having looked on Youtube etc, it seems dyneema is too slippery to tie knots in.
I have successfully tied knots in 3mm dyneema for lashings etc, but this is 12mm.

I bought 20m of new 12mm dyneema, sheathed, to make up a bomb-proof non-stretch preventer for my dangerously heavy boom, basically to categorically prevent gybes when deep-reaching in light airs while a swell is running, and I'm off watch.
Previously, polyester line has been uncomfortably stretchy in this role.. it runs from the boom end, outside everything, round a block near the stemhead, then back aft again. So quite long.


Not sure what "uncomfortably stretchy" means but surely a bit of stretch will give a bit of shock load absorption. Dyneema will not.

Yes I deliberately decided to try Dyneema because it won't stretch at all..may be a mistake.. I just want to pin the boom in one place, just off the rigging, and having tried it with polyester, it can move when a swell or gust puts the main momentarily by the lee. We shall see!

 

[thinwater]

Is this a B&R style rig, with swept back spreaders?

 

[Ohlin Karcher]

Is this a B&R style rig, with swept back spreaders?

No she's an old relic with a heavy wooden boom (250 kg -ish) and it has knocked me cold once already :encouragement:

(what is B + R ? )

 

[thinwater]

No she's an old relic with a heavy wooden boom (250 kg -ish) and it has knocked me cold once already :encouragement:

(what is B + R ? )

The reason I asked is that the farther back you keep the boom, the more critical low-stretch is for preventers. Swept back rigs is the reason race boats (volvo and Clipper) have been having trouble with them. The sweep places more strain on the line.

 

[Ohlin Karcher]

The reason I asked is that the farther back you keep the boom, the more critical low-stretch is for preventers. Swept back rigs is the reason race boats (volvo and Clipper) have been having trouble with them. The sweep places more strain on the line.

Makes sense..

 

[[3889]]

I'm not sure about the cow hitch as a solution, although dyneema is so strong that I agree it's likely that something else will break first. Having just re-read my Yachting Monthly article on this very topic, they recommend the scaffold knot for dyneema. Your favourite search engine will reveal all.

You may be right as I cannot now find the source of this claim. I would say, on an entirely anecdotal basis, that I snapped my original 8mm dyneema strop at the splice (ab)using a manual 32 winch. Not managed that so far with a cow hitch but maybe I've become more prudent.

 

[lw395]

I've always thought there should be some give in a preventer.
If you roll the end of the boom into the water when you're going at 8knots, that's a lot of force if there's no give at all.
But actually, dyneema is surprisingly springy when you've got a long length of it.

Dinghy racers using the small sizes often use ordinary knots, with a single overhand knot in the end of the line. I prefer to splice things that don't need undoing.

 

[Ohlin Karcher]

I've always thought there should be some give in a preventer.
If you roll the end of the boom into the water when you're going at 8knots, that's a lot of force if there's no give at all.
But actually, dyneema is surprisingly springy when you've got a long length of it.

Dinghy racers using the small sizes often use ordinary knots, with a single overhand knot in the end of the line. I prefer to splice things that don't need undoing.

Good point about the boom going in..but 8 knots would be in a dream only :encouragement:

(at least, on that point of sail anyway..)