Stealth mode - New Generation Ropes

[s/v Jedi]

But I can take pictures :-)

The blue lines would be the bridle.

[Seaworthy Lass]

Originally Posted by s/v Jedi

But I can take pictures :-)

The blue lines would be the bridle.

Yep, that is what I imagined .

I am back on board so give me a few minutes and I will put together and photograph what I meant by a simplified version of this.

SWL

[thinwater]

Is there ANY data that suggest cow hitching an eye reduces strength or that chafe is possible? I've done pull testing, and they don't break at the knot, they break at the end of the bury. Like a rope-to-chain splice, there is not movement in the hitch and thus no chafe.


There is no throat spread unless the the apex angle is greater than 90 degrees, which no one is suggesting. 60 degrees is the common minimum. Thus, no reason to discuss throat spread in this context. This, I believe, is mathematically clear based on geometry and engineering statics.


The more interesting case, to me, is the side load when the boat yaws and only one leg is loaded. The practical cure is to keep the rode eye long enough that the change in pull geometry is trivial and the cow hitch does not slide. There is a finite amount of friction, proportional to the load, and so long as the critical angle is not exceed, it will not move, anymore than you will slide on a 2% grade.


In other words, so long as the rode eye splice is long enough, there is nothing wrong with the standard design. I have not heard mention of a failure, or did I miss that? (The figure 8 does not count--that was an error introduced by trying to improve on a strong, simple design.)

[Seaworthy Lass]

Using 2 second splicing :

There is no need for three cow hitches.
Jedi, just retain the first cow hitch you mentioned - the one on the end of the leader.

It’s quite a simple solution I think. Make the eyes of the bridle legs extra long so there are no throat issues.

SWL

[Seaworthy Lass]

Originally Posted by thinwater

Is there ANY data that suggest cow hitching an eye reduces strength or that chafe is possible? I've done pull testing, and they don't break at the knot, they break at the end of the bury. Like a rope-to-chain splice, there is not movement in the hitch and thus no chafe.


There is no throat spread unless the the apex angle is greater than 90 degrees, which no one is suggesting. 60 degrees is the common minimum. Thus, no reason to discuss throat spread in this context. This, I believe, is mathematically clear based on geometry and engineering statics.


The more interesting case, to me, is the side load when the boat yaws and only one leg is loaded. The practical cure is to keep the rode eye long enough that the change in pull geometry is trivial and the cow hitch does not slide. There is a finite amount of friction, proportional to the load, and so long as the critical angle is not exceed, it will not move, anymore than you will slide on a 2% grade.


In other words, so long as the rode eye splice is long enough, there is nothing wrong with the standard design. I have not heard mention of a failure, or did I miss that? (The figure 8 does not count--that was an error introduced by trying to improve on a strong, simple design.)

Hi Thinwater
This is the situation when you cow hitch the bridle to the leader rather than the other way around. It is the physical size of the hitches that are the problem.

The throat angle problem can partly be solved by making the eye of the leader very long, but the hitches will still want to slide around the slippery dyneema to the central position when load is only one one leg. It may only be a few cm, but it will be moving back and forth.

I think cow hitching the other way as Jedi suggested, but only having one cow hitch solves the issue.

SWL

[Seaworthy Lass]

The above is the situation using only 5 mm dyneema. It will be MUCH worse using my 12 mm or Dockhead’s 14 mm rope diameter, as the angles won’t scale up with rope size, but the cow hitch will be very much larger.

Maybe Dockhead can post a photo of what it looks like in 14 mm keeping the 2.5:1 proportion for the leg length: attachment distance to maintain the correct angle. I don’t have any loose 14 mm on board.

SWL

[Seaworthy Lass]

Originally Posted by thinwater

Is there ANY data that suggest cow hitching an eye reduces strength or that chafe is possible? I've done pull testing, and they don't break at the knot, they break at the end of the bury. Like a rope-to-chain splice, there is not movement in the hitch and thus no chafe.

Have you actually tested 14 mm bridles with both legs cow hitched on in the configuration that is occuring here?

(Edited to add: Sorry, re-reading that sentence it sounded awfully rude. I wrote it in a hurry, so it came out abruptly. It was a genuine query though.)

I am not aware anyone has done this. I have found no data. Nor have I heard of UHMWPE drogues failing for this reason, but how many UHMWPE drogue have been subject to extremely high loads when deployed? Have any been exposed to the “once in a lifetime” load Jordan was discussing?

This is very new territory. Just because no failures have occured yet using the method Dockhead drew for attachment, doesn’t mean they won’t.

I don’t think there is any harm in trying to make up the drogue as safely as we can, particularly if there are easy solutions possible. Tearing forces at the throat of any eye are not an academic concern.

Even if cruisers continue cow hitching the legs of the bridle to the eye of the leader, as most seem to be doing now, at least this discussion may alert them to make the eye of the leader long enough that any tearing forces at the throat of the eye of the leader are minimised.

Eye length has never been discussed before for the construction of these drogues. If anyone makes the length eye of the leader very short then cow hitches the bridle legs on, I think it is possible they will have serious problems.

SWL

[Seaworthy Lass]

We cannot possibly know how many cruisers have attached the bridle in this manner and their UHMWPE drogue it is sitting in their locker waiting for a disaster to happen.

In this rough mock up the throat angle is around 60°.
If this is duplicated in real life, the tearing force at the base of the throat is 29% of the entire load on the system.

Thinwater made the observation that he thought there would be no problems as long as the eye splice was long enough, but how many cruisers making up this bridle are aware of that?

[s/v Jedi]

Originally Posted by Seaworthy Lass

Using 2 second splicing :

There is no need for three cow hitches.
Jedi, just retain the first cow hitch you mentioned - the one on the end of the leader.

It’s quite a simple solution I think. Make the eyes of the bridle legs extra long so there are no throat issues.

SWL

Agreed, this seems to be the most simple and thus the best solution. Now we wait for someone to make me eat my words and come up with something even better

[Seaworthy Lass]

Originally Posted by s/v Jedi

Agreed, this seems to be the most simple and thus the best solution. Now we wait for someone to make me eat my words and come up with something even better

Jedi, this is where throwing around ideas is so useful .

I (and everyone else it seems) for some reason had blinkers on and we were focussed on how to connect two legs to one, rather than alternative option you presented of connecting one to two. It was like a light bulb was switched on when I read what you wrote.

Yes, there may be better solutions and yes, there may be something wrong with this one that I can’t see that someone will point out, but the mock up looked very promising. It would be good to try and reproduce this in the cockpit somehow and add some load via a winch and see exactly what happens at the junction when the load is equally distributed between the legs, then when it switches to one. Something may show up.

SWL

[thinwater]

Originally Posted by Seaworthy Lass

Hi Thinwater
This is the situation when you cow hitch the bridle to the leader rather than the other way around. It is the physical size of the hitches that are the problem.

The throat angle problem can partly be solved by making the eye of the leader very long, but the hitches will still want to slide around the slippery dyneema to the central position when load is only one one leg. It may only be a few cm, but it will be moving back and forth.

I think cow hitching the other way as Jedi suggested, but only having one cow hitch solves the issue.


SWL

Have you tested this under some load? My thought is the reverse, that one hitch allows more movement. But testing would convince me. If not, I think I will take this on. Curiously, the results with Dyneema and polyester may be different. I suppose I shroud test both, though I can't see why I would use polyester for the bridle.



Yes, a short eye is dumb. I would think that was obvious... but so is a figure 8. So that makes it a story worth telling!

[Seaworthy Lass]

Originally Posted by thinwater

Have you tested this under some load? My thought is the reverse, that one hitch allows more movement. But testing would convince me. If not, I think I will take this on. Curiously, the results with Dyneema and polyester may be different. I suppose I shroud test both, though I can't see why I would use polyester for the bridle.

I will try and rig something up in the cockpit today. I have no 14 mm UHMWPE, but I have some 8 mm loops already made up. The % of breaking load I can apply to 8 mm is low, but I think this situation doesn’t scale up well, so using 3 mm may be misleading. If I can set something up well, I may try both, as I can load 3 mm up decently.

I could be way off base with this, but Jedi’s “cow hitch the leader” idea looks right enough that it is worth the trouble.

Originally Posted by thinwater

Yes, a short eye is dumb. I would think that was obvious... but so is a figure 8. So that makes it a story worth telling!

I miss lots in other areas that is obvious to others. What is instinctive to one person, may take ages to sink in for someone else. Maybe to some people a short eye looks neat and snug. Maybe they think an eye that looks a bit like an eye going around a thimble is ideal. Hopefully no one has made up the very short eye I showed, but there may be ones sitting in lockers that are short enough to cause problems with tearing forces at extreme loads.

There are no detailed instructions anywhere on how best to put together the drogue using UHMWPE. Not even much discussion. Most of the articles involve the use of polyester. Up until very recently there was even debate about whether a low stretch rope was actually suitable in this application.

Before we headed off to Scotland a year ago, I downloaded every article I could find, plus links to all the CF discussions and I was still left floundering with what to do. I even felt clueless about how best to weave in the cones and how to secure the webbing. The recommended figure 8 just didn’t sit well and was very hard to tighten down in the precise spot I wanted the stopper (it needed to be precise for the cone to sit straight). I couldn’t tie a precise double overhand at all, as the webbing is black and there I had no easy way of marking it short of stitching some thread through, and I didn’t fancy stitching a thousand+ bits of webbing. I settled for two lots of overhands, which seemed super snug, but who knows. At least the loads on each individual cone are low so decisions are less critical here.

Some general recommendations are needed for basic things such as tail bury length, weaving Brummel locks or stitching, cow hitching or looping the eyes through each other, pattern of weaving the cone tape (one or two passes, 90° bends or more oblique), how loose to leave the cones (to allow full opening or a bit more or a lot more), what stopper knot to use, etc etc. Even some reassurance that it doesn’t matter a scrap which alternative you use (which I doubt is the case) would be helpful. There is just very little guidance available for UHMWPE, either from the experts or the manufacturers of the rope or the manufacturers of the drogue.

The Shark manufacturer said they used thimbles with no exact indication of thimble or shackle size etc, then disappeared from the conversation just when they were needed :

Originally Posted by Fi2010

Using two rodes with thimbles connected to the JSD or speed-limiting drogue rode via shackle works best. We realize the JSD suppliers haven't recommended this setup

I am sticking my neck out on a block saying I think this is wrong, but that is my opinion.

The bridle junction is the point that sees the highest loads, and they are flipping from one leg to another. Techniques that are perfectly reasonable under low loads may fail here. This is one spot I think we really need to get it right. As a starting point, simply a calculation of throat angles and resulting tearing forces for different proportions of line diameter to eye length would be a useful guide if the two bridle legs are being cow hitched on.

A simple statement of “make the leader eye length a minimum of x times the bridle line diameter if cow hitching the bridle eyes onto the leader eye” would be a helpful starting point.
This seems to generally the current method used for attaching the bridle by cruisers making one themselves using UHMWPE.

SWL

[fxykty]

Originally Posted by Seaworthy Lass

Using 2 second splicing :



There is no need for three cow hitches.

Jedi, just retain the first cow hitch you mentioned - the one on the end of the leader.



It’s quite a simple solution I think. Make the eyes of the bridle legs extra long so there are no throat issues.



SWL

Wow, this is awesome! Thanks so much!! This thread shows how this forum can be amazing.

The next question that I think you may have answered is how to thread and secure the cone webbing. The Ocean Brake instructions are for double braided polyester line, so the poke through and figure 8 knot for each webbing may not be best (but maybe at least adequate?) for use with single braid UHMWPE line?

When you mention tying two overhand knots, is that one after the first poke through, then another poke through and the second?

[oldbilbo]

Originally Posted by thinwater

Have you tested this under some load? My thought is the reverse, that one hitch allows more movement. But testing would convince me. If not, I think I will take this on.

Yes, a short eye is dumb. I would think that was obvious... but so is a figure 8. So that makes it a story worth telling!

You may care, if setting up a pull-test rig, to look at using a 'Prusik' hitch as alternative to a 'Cow' hitch.... i.e. one more round turn.... to see if that has discernible benefit. I suspect it may well do so.

[Seaworthy Lass]

Originally Posted by fxykty

Wow, this is awesome! Thanks so much!! This thread shows how this forum can be amazing.

The next question that I think you may have answered is how to thread and secure the cone webbing. The Ocean Brake instructions are for double braided polyester line, so the poke through and figure 8 knot for each webbing may not be best (but maybe at least adequate?) for use with single braid UHMWPE line?

When you mention tying two overhand knots, is that one after the first poke through, then another poke through and the second?

Fxy, don’t get too excited, all this is speculative on my part and I do not have any expertise here, just enthusiasm. It would be very good if Thinwater could test this bridle arrangement. I have no load testing equipment. In addition, load testing does not duplicate the the condition the bridle is subject to as the boat yaws around. I think there are a lot of unknowns. There is still much to learn about UHMWPE.

It would be good to have a few others chime in regarding how to secure the cones. I just winged it and I would hate to give wrong advice. The knot I used was an overhand with a second overhand tied over the top to give it bulk, tied after the second pass through of the webbing. I did pay particular attention to making sure the staggered legs of the webbing were the right length to allow the cone to open evenly centred exactly on the line. Hence the need for the position of the stopper knot to be precise. This was time consuming. I am only partly through.

SWL