Down and Dirty Dyneema Strops

[estarzinger]

Originally Posted by Seaworthy Lass

Do you mean the dyneema strands? No, I don't like the thought at all of whipping twine cutting into the dyneema.

No, no, not whipping twine. The idea was to tie the accessory cord (the stuff you are using to join the dyneema legs) to the dyneema, just below the cow hitches, with something just a bit more secure than a clove hitch - one of the constrictor type. This is lower profile than the stopper knot idea.

SWL

.......

[estarzinger]

Originally Posted by Dockhead

Someone asked to see the strops in action. Here is my twing system:

It looks like the whipping on the top strop has slipped down and no-longer has the ring fully captive?



It strikes me that these whippings should be tied in place while the strop/ring is loaded (just say on a bench or between two winches). That would allow getting the distance between the two legs exactly right and ensure there is no pressure/force pushing the whipping away from the ring.

We are lucky to have you to test these, because your loads are near the top end of actual cruising loads. I was actually surprised that your original messy whipping came apart - do you know if the cord broke - or did the whipping pull apart?

[Seaworthy Lass]

Originally Posted by estarzinger

It looks like the whipping on the top strop has slipped down and no-longer has the ring fully captive?

I am trying to work out why this happened. Load on the legs should not make anything slip down unless the reef knot failed (it looks intact) or the cord has snapped (in which case it would all unravel).
It is only one that has done this.
Was the lacing maybe too close together so it is now being forced down to where the legs are closer together? The only way it can be forced down though is by pulling on the lacing and this would only tighten it and be counterproductive.

Dockhead, was anything different with the lacing of this one? The cord coming up from the base of the lacing seems interwoven rather than passing through the centre on one side. The overhand at the base of the lacing is missing so the cord coming up from the base is skewed. Is this the same on all of them?

The most likely thing I think is that cord was not snug on the ring when it was cinched and tied off. Maybe the dyneema trapped it a bit higher.

Originally Posted by estarzinger

It strikes me that these whippings should be tied in place while the strop/ring is loaded (just say on a bench or between two winches). That would allow getting the distance between the two legs exactly right and ensure there is no pressure/force pushing the whipping away from the ring.

Excellent idea. The binding could not quite be finished, but the lacing is the critical bit and that could be done, the cord fed up and the ends crossed ready to go around the low friction ring. Maybe then this crossed junction could be clamped with a temporary constrictor, the strop unloaded and the ends of the cord then passed around the ring and cinched with the reef knot

Originally Posted by estarzinger

We are lucky to have you to test these, because your loads are near the top end of actual cruising loads.

Here, here .

[Seaworthy Lass]

The problem of achieving a perfect fit with the lacing could be helped by using cord with a bit of stretch to it.

Eg Braided 3mm nylon:
http://www.renconets.com/3-0mm-braided-nylon-twine

Unbraided would be better, I will have a hunt.

[Cruisingscotts]

SL, I think your concept is fine and looks to be quit easy to do. I would make the following changes.

As the pic shows things move when loaded, possibly the strop set or?
I would eliminate the tails going around the ring to lock it in place. I think this creates point loading on the ring due to the strop not making uniform contanct with the internal radius of the ring. In a extreme loading scenerio this could lead do the lip of the ring deforming or cracking where the working line passes through and the arm it creates.
I would bring your lashing tails through the ID of the ring in opposing directions and back through the inside of the weave as you originally did. Then partially load the arrangment and begin working everything into place pulling tight. Increaseing the load as you go. When fully loaded on a winch I would finish the tails with whatever knot or constrictor you choose.

The posted pic is why I alway try to load the arrangment before seizing as things always seem to move or creep some.

[Seaworthy Lass]

Originally Posted by Cruisingscotts

SL, I think your concept is fine and looks to be quit easy to do. I would make the following changes.

As the pic shows things move when loaded, possibly the strop set or?
I would eliminate the tails going around the ring to lock it in place. I think this creates point loading on the ring due to the strop not making uniform contanct with the internal radius of the ring. In a extreme loading scenerio this could lead do the lip of the ring deforming or cracking where the working line passes through and the arm it creates.
I would bring your lashing tails through the ID of the ring in opposing directions and back through the inside of the weave as you originally did. Then partially load the arrangment and begin working everything into place pulling tight. Increaseing the load as you go. When fully loaded on a winch I would finish the tails with whatever knot or constrictor you choose.

The posted pic is why I alway try to load the arrangment before seizing as things always seem to move or creep some.

Thanks for the input.
Mulling over Dockhead's photo of the loaded strop and the way the lacing has slid down, I can see that there could be problems I had not considered before. In addition, it makes me wonder if chafe due to the cord and strop rubbing on each other around the ring may in time be an issue.

If the ID of the ring is used to attach the lashing, I think you would need to start with that though, not finish, as if the LF ring tries to flip out, then all the force it taken purely by the final knot. It would be better if the lacing absorbed that and the final knot was just to bind the arrangement.

I don't know what kind of forces we are dealing with when the ring tries to push out. Will the cord simply snap then? Maybe for this reason thin dyneema would be better as the cord material? Although one thing that makes me think the forces can't be too high, is that velcro and dyneema seem to be doing the job adequately on big rigs, so maybe the cord snapping is unlikely if it is not being restricted by the sides of the strop to start with.

The sides of the strop must feel (and behave) like steel under load. Soft shackles certainly do when I pretension them on the winch. Given this, it puzzles me when a Brummel lock is used to bind the LF ring, that strop strength is only reduced by 20%. I would have imagined the strands of the dyneema at the entry point would be stressed badly.

Jumbled thoughts just running through my mind .

Anyway, I will make up what I think you are describing and see how it looks/feels.

Back to the drawing board.

SWL

PS A 20% loss of strength with a Brummel lock near the LF ring is starting to look very favourable .

[Seaworthy Lass]

CruisingScotts, is this what you mean?

I started with the lacing and threaded the cord up the weave of the lacing exactly as before, but then passed the cord through the ID in opposite directions, then back down the weave of the lacing and secured:



The loading does not feel right if I try and force the ring out manually. It is all on the final knot.
I will repeat this starting by looping the cord through the ID first and see how it goes.

SWL

[Cruisingscotts]

Originally Posted by Seaworthy Lass

CruisingScotts, is this what you mean?

I started with the lacing and threaded the cord up the weave of the lacing exactly as before, but then passed the cord through the ID in opposite directions, then back down the weave of the lacing and secured:



The loading does not feel right if I try and force the ring out manually. It is all on the final knot.
I will repeat this starting by looping the cord through the ID first and see how it goes.

SWL

Roger,

Except I would add one other change, add several more tucks/weaves on the ring end and exit / enter the tails below these weaves, ring depth plus one or two. If tensioned under load the portion closer to the ring can still maintain the gap you are after and the lower end, which is locking the tails in both directions, can be made tight for several tucks/weaves lockign the tails. A little more fid work to make things even and happy. You should still be able to rotae the ring freely with no load but cpative so it cannot come out of the strop.

As a side, my untested theory on using smaller twine seizings is that they are sort of a tell tail for loading. I try to make things well above what I think they will see. If a siezing is opening up or breaking it's back to the drawing board.

[Seaworthy Lass]

Originally Posted by Cruisingscotts

Roger,

Except I would add one other change, add several more tucks/weaves on the ring end and exit / enter the tails below these weaves, ring depth plus one or two. If tensioned under load the portion closer to the ring can still maintain the gap you are after and the lower end, which is locking the tails in both directions, can be made tight for several tucks/weaves lockign the tails. A little more fid work to make things even and happy. You should still be able to rotae the ring freely with no load but cpative so it cannot come out of the strop.

As a side, my untested theory on using smaller twine seizings is that they are sort of a tell tail for loading. I try to make things well above what I think they will see. If a siezing is opening up or breaking it's back to the drawing board.

Thanks .

Not having a lot of success here, but I am a long way from exhausting the possibilities.

I have found that unless the first few lashings are actually tucked under the ring before the cord passes through the ID, so matter how well secured the turns are that pass through the ID, the ring just freely slides around as the cross section is roughly a semicircle. It needs almost no force to do this - just the barest push with my fingers and the ring moves 90°. The low friction is working against me here .

I will work on keeping the lashing high, but the way Dockhead's slid down is not encouraging.

SWL

[estarzinger]

A slightly different take on SL's simple approach, with three objectives (1) allow the dyneema a bit more motion without stressing the cord, (2) while fixing the whole configuration in a way that does not allow the dyneema to slip/slide away from the ring, and (3) do something decent with the tails.

I tied it around a glass rather than ring - so the ring edge does not obscure anything.

Bottom - two clove hitches (could be cow hitches as SL used - I just like cloves better). They are not joined directly to each other - one way this allows a bit more motion without stress.



Top - There is also a clove hitch at the top (this is tied first in the middle of the cord - then the two lower cloves) - This prevents the dyneema from slipping/sliding up thru the two at the bottom - it 'triangulates' the whole thing in place. It also acts as a clamp for the tail ends - they each go under this clove. I then put stoppers on them here - would probably sew them in a real application. But these stoppers would mostly be hidden/protected by the ring flange.



I am not immediately a fan of tying the cord thru the inside of the ring - I understand the purpose - but it seems vulnerable to being possibly burned/worn by big sheet eases - and the objective can seem to be accomplished around the outside of the ring.

edit - just for scale - this is 12mm dyneema and paracord.

[Dockhead]

Originally Posted by estarzinger

It looks like the whipping on the top strop has slipped down and no-longer has the ring fully captive?

Attachment 127965

It strikes me that these whippings should be tied in place while the strop/ring is loaded (just say on a bench or between two winches). That would allow getting the distance between the two legs exactly right and ensure there is no pressure/force pushing the whipping away from the ring.

We are lucky to have you to test these, because your loads are near the top end of actual cruising loads. I was actually surprised that your original messy whipping came apart - do you know if the cord broke - or did the whipping pull apart?

The loads are huge -- it's a very high aspect carbon laminate blade which needs very great tension on the leech.

I think the lacing slipped down just because this one was tied loosely -- I couldn't figure out how to regulate the tension, and tried one laced loosely -- this was that one. The ring is still captured and I'm not sure this is a bit problem -- I think probably just needs to be cinched down a bit tighter. The other ones did not suffer from this.

The old ones pulled apart like all my ones from last year -- from "pumping" of the legs, I'm sure. The key thing in my opinion is to isolate the knots from any flexing and to reduce the throat angle as much as possible. I think SWL's lacing is very good and I'm planning to stick with it for a while anyway.

[Seaworthy Lass]

Lots to mull over. I am not having much success trying to use the ID to secure the binding.

My eyelids are being held up with matchsticks at the moment so it is time to hit the sack. Thanks everyone for all the interaction today. I will have another play with this tomorrow.

SWL

[estarzinger]

Originally Posted by Dockhead

The old ones pulled apart like all my ones from last year -- from "pumping" of the legs, I'm sure.

but did the twine break? or did the whipping come undone without the twine breaking?

The specific failure mode makes a difference in how we tweak the designs. one is more about loads and strength and the other is more about security.

[Dockhead]

Originally Posted by estarzinger

but did the twine break? or did the whipping come undone without the twine breaking?

The specific failure mode makes a difference in how we tweak the designs. one is more about loads and strength and the other is more about security.

No, didn't break -- just came unraveled, no matter how I tied them. The cyclical stress just pulled them apart.

My sewn ones from the original post of this thread came apart exactly the same way, and on the first time out.

The SWL-style lacing did NOT come apart, and looks quite good after a hard day of sailing today, other than the overly loose one which slid down the legs.

[estarzinger]

Originally Posted by Dockhead

No, didn't break -- just came unraveled, no matter how I tied them. The cyclical stress just pulled them apart.

My sewn ones from the original post of this thread came apart exactly the same way, and on the first time out.

Thanks - interesting.

Just trying to figure the difference between your failure and the antal (and many other) commercial strops (which are reliable) and are essentially a 'whipping' made of a whole bunch of half hitches. I dont know exactly how they terminate the ends of the whipping - must be pretty secure - will have to look into that.





This solution is not as good (IMHO) as the designed we have discussed in this thread . . . . but they do work (including on volvo and open 60 type loading) and don't unravel - when done 'correctly'.

The trapezoidal lacing and the 'simple' should by design both be immune to high loads and cycling loads, if done correctly with a near zero throat deflection. And if laced on when the strop is loaded they should be near fool proof to be done correctly. You only need to make sure they are close enough to the ring to insure capture and inversion prevention.

I personally use a completely different approach - but it is unmentionable here because it uses sewing and VHB tape