Jordan Series Drogue in Dyneema

[BigBeakie]

Oldbilbo,

I think that's fair, and well reasoned. And you're right to look for evidence based solutions. I try and do the same.

To my knowledge from reading of the testing done by Brion Toss and Evans Starzinger, the pioneers in marine application of Dyneema, the bend radius requirement for very high strength applications was lower than the wire rope industry standards, which from memory were around 5:1. I believe Evans got results showing somewhat greater than 1:1 yielded almost full breaking strength in a properly constructed full bury eye splice.
Also one of the other factors that was important, as discussed by SWL in her excellent information, was the throat angle "tearing" force on the eye splice when using thimbles. The narrower the angle, the better. Again, I believe this concern arose from empirical break testing by EStarzinger.

The guys over at the Youtube channel How NOT to Highline, do break testing of Dyneema for climbing/highlining applications. Very interesting channel if you haven't seen it. Perhaps they could be persuaded to break a JSD setup on their rig to test the thimble vs soft eye splice attachment?

[oldbilbo]

Wholly agreed. If we continue delving for reliable information and sharing it on platforms such as this, we'll move forward..... which is, I trust, what Don Jordan would have hoped for.

While I don't have much detail on 'throat angle' considerations, I was aware of the concept and tried to accommodate the issue in the way I've secured these tubular thimbles, using an interlaced whipping. The thimbles themselves are larger than they otherwise might be. That results in a Bend Ratio ( internal ) of 3.5:1 and a Throat Angle of 18 degrees. I have since found some smaller and smarter s/s thimbles, which would give a Bend Ratio of 2.5:1 and a Throat Angle of 20 degrees.

BYW, I have sleeved my eye-splice loops in tubular antichafe - just in case!

Perhaps someone might care to comment.

[Fi2010]

The pioneers of Dyneema testing, amongst other unique marine gear, are owed to the energy companies. They had to come up with lighter and stronger materials/methods for laying cable and oil pipes in our Oceans. The offshore work boats look like something from Star Trek. You should check it out sometime. It’s completely insane.

The best bridle setup is what most of the drag device companies have used for decades, except the JSD suppliers. A two rode bridle shackled to a single rode leading out to the drag device or in your case, a single rode with cones.

Our company founder started using this simple bridle back in 1947. We still build the fixed bridle setup for our customers. Happy to report a zero failure rate after 74 years in the business.

Our fixed bridles are commonly used by multihulls for para-anchor deployment as well. Same success rate. Any rigger should be able to put together this type of bridle. Brian Toss built several bridles for our customers in Washington State. Brian’s workmanship was completely amazing. Brian passed away too soon. We lost an incredible giving, honest, and wonderful human being.

[BigBeakie]

Pleased to see you respected the work of Brion. You could at least try and spell his name correctly[emoji849]

[oldbilbo]

Originally Posted by BigBeakie

Pleased to see you respected the work of Brion. You could at least try and spell his name correctly[emoji849]

From what I can find to read, he certainly make a favourable 'set of ripples on the water'.


Oh, and I understand Wm. Shakespeare signed his name in 26 accredited ways. There's hope for us all....

[oldbilbo]

Following on from parts of my post #195 and subsequent comments, I have queried several of the significant rope makers and users about 'D:d ratios'. So far, they are in close agreement, although should I have an 'outlier' response I shall delve deeper into that to determine if it is simply anomalous or whether there's good reason....

Here's what the Tech Testing people at English Braids replied, and Marlow Ropes agreed....

"Wil has clearly researched this device ( JSD ) and noted the potential issues with some of the available assembly techniques. I would not recommend any form of hitch, knot or choke; as these are all proven to weaken a rope. The bridle angle, as described, should be a maximum of 20 degrees, so as to maintain the strength.
To couple the legs to the main line; I prefer to use a tubular thimble with a gusset. Best go a size up; 12mm to ensure that the rope is well encased in the open section. Each of these may be secured by either a Brummel or Shoemaker long bury splice. A tubular sleeve can be fitted, but depending on size; the thimble may have to increase. A 12mm thimble has 27mm clearance, so there’s limited space for a bow shackle. These are also a bit low in WLL at a size to fit. A soft shackle has the capability to hold load, and these are quite often employed in towing bridle assemblies. Our 12mm item has an average break load of 12300kg, so would be adequate, based on Wil’s data. My only reservation would be the cyclic nature of the environment. The shackle is effectively secured with a ball knot and loop (monkey fist etc.). These tighten up under load and hold fast, but I have no data to confirm what happens if that load is repeatedly lost.

The final piece of the puzzle would be the stern attachment. The force on the line is divided between the two points, so it would be feasible to use a shackle here. Needless to say, that the anchor point must be of a strength to withstand the load."

I also asked John Franta of Colligo Marine, during his recent 'Live Event'.
( https://www.facebook.com/25917993036...41193019795193 )
His response ( from 23:07, at 25:00, and to 28:30 ) is illuminating and unequivocal - "I would never do a One-On-One on anything".

Based on the above, I'm going ahead with the use of a soft shackle joining rode to bridle-arms - each of the 3 parts with tubular s/s shackles of >5:1 D:d as shown above, ensuring an angle of <20 degrees. The soft shackle is of 11mm D12 Marlow Dyneema which has a published Min Breakload of 10700kg/23540lb. In a simple loop, I've used a conversion factor of x1.6, indicating a Min Breakload of 17120kg/37664lb. When doubled-over again in an Improved Soft Shackle, the overall gain is of the order of 230%

https://www.youtube.com/watch?v=K0eZz36PRYI

...which offers me 24610kg/54162lb. That's over 6 times the Max AUW of my boat and over 9 times Don Jordan's calculated Maximum Design Load.

I'll also have a double layer of antichafe tubing slipped on. Lots of 'belt and braces'.....

I've considered the expressed concern that the S/Shackle's noose might relax during cyclic unloadings and open uncommanded. The same notional possibility exists with steel bow shackles; that's why we use locknuts, drilled holes, R-pins and locking wire. On my OTT Soft Shackle I shall use a reusable nylon cable tie, wound 2-3 times around the throat of the noose and pulled secure. That will not budge without the use of tools.


Oh, and my soft shackles are made by an acknowledged industry pro, who does a rather better job than I could.



I have had no response from New England Ropes to the same query.

[Dockhead]

Originally Posted by oldbilbo

. . The thimbles themselves are larger than they otherwise might be. That results in a Bend Ratio ( internal ) of 3.5:1 and a Throat Angle of 18 degrees. I have since found some smaller and smarter s/s thimbles, which would give a Bend Ratio of 2.5:1 and a Throat Angle of 20 degrees.

BYW, I have sleeved my eye-splice loops in tubular antichafe - just in case!

.

Do you mind sharing your sources for tubular thimbles, and antichafe sleeves? I think many of us would be interested.

[Breaking Waves]

Originally Posted by Dockhead

Do you mind sharing your sources for tubular thimbles, and antichafe sleeves?

Dock (some thoughts until bilbo directly answers you),

The tubular thimbles are standard commercial rigging parts. Samson offers a range specifically for high-mod rope (generally they are used for wire rope). Whatever is your best commercial rigging distributor would certainly offer them (or the EU equiv).

There are, as usual, a range of quality/specifications on these thimbles, so you need to match specs with the rope you are using. Also, on some of them (some of those aimed at wire rope) it is worthwhile rounding off the edges just a bit (with like a Dremel) .

Both NER and Yale offer very nice tight weave dyneema chafe sleeves and Samson offers somewhat more industrial options.

The splices and thimbles bilbo is using are standard commercial proven applications/solutions - unlikely to be any problem with them (so long as the specs on the thimbles are correct and the splices well made). I would comment as an aside, that for splice strength, a very nice fine taper is the more critical factor than the 72x bury You can in fact go down to 45x-ish and not lose static strength, the extra length is really more about low load slipping which is not much of an issue if you sew and then proof test/set the splices. While it is not hard to lose 5% strength with a blunter than optimal taper. So if anyone here wants to 'boast' about how good your splices are, boast about your tapers and not your bury lengths

The only part of Bilbo's solution which is non-standard is the use of the soft shackle to join the three thimbles. Given the size of the soft shackle he is using and the fact he has a relatively small boat, I would be quite confident it will work for him. I personally doubt he will ever put even 2k kgs on this. But for a more stressed application, I think I would want to do a bit of testing of that application. There is a more obvious textile way to connect those three thimbles, but it would be 'permanent' and not allow you to separate them easily, and I would still want to test it. This thimble approach was not/would not be my personal choice of solution, but it is a reasonable option (with the 'needs testing' caveat for a more stressed application).

[Breaking Waves]

a couple of people asked me questions about the above - thought it worthwhile to post a short summary.

1. Why would you feel the need to 'test' the soft shackle as they are quite a proven solution?

Soft shackles are commonly used and tested in a two-point load situation. I have never seen one tested in a 3 point load situation. My best guess is that it will be fine. But it is striking how often we discover something a bit unexpected when we test dyneema in a new application. There are often a few known unknowns but it is the unknown unknowns that frequently produce surprises. So, in critical applications, it is almost always worthwhile to test.

In this particular case, in static testing - it would be worth confirming that 'hoop loading' does not cause a problem, that having one of the thimbles bare on either the loop or the noose does not cause a problem (it does not in 2 point loading, that is well known, but the strain angle will be different in 3 point loading), and personally, I am skeptical of the use of the wire tie to close the loop (I think it will either slip or break or if neither of those it could create a stress riser) so that is worth testing. In dynamic testing, one would want to know about wear/chafe from the thimbles, the behavior of the loop under cyclic loading (personally I don't think this is any sort of issue with a properly sized loop, we essentially see no accidental openings in 2 point loading applications) is worth looking at. And then in both static and dynamic cases - there is always the possibility of learning about some currently unknown unknowns. I guess it will be all ok, but on the other hand we might learn something new.

2. What is the 'more obvious textile way' (than the soft shackle) you refer to?

A multiple loop, with end-to-end bury, with a Dyneema chafe cover. Benz has talked about these in other threads. This is the highest strength (almost twice the strength of the soft shackle using the same amount of dyneema) most proven approach. It still is textile, and so is potentially vulnerable to some things, but eliminates the weaknesses of the loop/knot. However, it is permanent, I don't think that should be much of a problem unless you are planning to regularly remove your bridle legs from the rode (if for example, you might be planning to also use those logs for some other purpose).

3. You say this would not be your personal solution - what would be?

I like the solution Saltylass and Fixxty have shown. It is quite elegant - light, compact, no metal to clang around, strong, and well-proven. There is a small and well-defined weakness in that bridle connection (strop join), but that is very easy to compensate for with just one size bigger line at that point.

I have mentioned before if you want to do this in the most 'proven industrial' way, then using a delta plate is the solution. That unfortunately means a pretty large chunk of metal. If you want to spend a little money, you can get an engineer to FEA the delta plate and a machine shop to remove quite a bit of less stressed metal, and you can do it in Ti (I have personally done this for two high spec applications) or high tensile aluminum, all of which will make it elegant and lighter. This is perhaps the strongest and least vulnerable of any solution (which is why it is standard for heavy lifting) . . but it is still a decently sized chunk of metal. For most of our 'yachting applications,' I think the zero metal strop is probably preferred - easier to handle and certainly strong enough.

4. Care to comment on the quotes about knots and 1:1 bends?

The engineering is really quite well established and there really is zero controversy about this (among those who understand the engineering).

One needs to understand that there are two different cases here, and people sometimes get confused between them. Case one is a bend in a rope with two loaded/working ends - for example, a rope over a sheave. Case two is a bend inside a closed-loop (like a spliced loop).

In case one, the various bend ratio charts (like the HAMPIDJAN chart John F refers to) apply directly. They show that a 1:1 bend will weaken the rope locally by about 50%. That is clear and unambiguous. And we know from pull testing that knots will weaken Dyneema by 50-65% (depends on the knot and the particular flavor of Dyneema). That is also clear and unambiguous. Given that, the advice to avoid knots and 1:1 bends in a case one application is understandable because you are giving away a lot of strength. However, I will comment that the strength loss is well understood and if you have an application where you absolutely need a knot or a 1:1 then it is quite simple to adjust the rope strength to compensate - so it is just simply an engineering problem and not something evil.

In Case 2, a closed-loop (like a spliced loop), the local strength within the loop is 200% (roughly, a bit of complexity for a few percent about throat angle and hoop loading). That is well proven and understood (I will note that John F originally did NOT understand this until Evans and Brion explained it to him, and Evans then did 3 series of tests to show that it was true and that his three theoretical counter explanations did not in fact apply). So, in this case, if you have a 1:1 bend inside the loop, it is a 50% reduction of a local 200% strength, which gives you in the end 100% strength (it is a bit less than this, like 95% typically because of the marginal complexities). This has been proven and tested very extensively (if you are curious there is the old SA thread where Evans did multiple test runs to demonstrate it to John F.). So, in case 2 applications 1:1 bends are rather more acceptable (just upsize the rope by a few percent if you really need totally 100% spec strength) - generally, it is accepted that 1.5:1 bends are totally accepted here (there are industrial rope fittings that use 1.5:1 bends). This is true no matter someone's hand waving about Dyneema compressive strength or scaling or dynamic action. I personally would still rather avoid a 'knot' inside a loop, because almost always there is a solution to avoid that ugliness. A strop hitch however does not have the great weaknesses of a normal 'knot' - it is a bit worse than a straight 1:1 bend ratio (it is a strength loss of around 15%, depending on a number of factor), and most commercial riggers will recommend you just do a simple interlinked 1:1 splice to splice if you can, but the strop is quite acceptable and well understood and you can easily upside the rope to compensate for its loss if it is the best solution for the application (it does prevent some wear/chafe that directly interlinked splices may experience). So, in case 2 bend ratios higher that 1.5:1 don't, in fact, add much strength, and if the throat angle is high (which it has historically been in some thimbles which have been focused exclusively on pushing bend ratios up) then it can in the worse case in fact be weaker. I will comment that there is potential long-term value in thimbles reducing wear at the contact point, however, Dyneema is incredibly wear-resistant and this is not a huge issue for most of our yachting applications (it is a bigger issue in some commercial applications).

This is all pretty well-proven engineering and not controversial. But sometimes people get confused between case 1 and case 2 applications.

[oldbilbo]

I'm pleased and grateful to note some development of the matter under discussion - both qualitatively and, I would hope, quantitatively. It certainly helps me develop my working towards the best kit I can carry, for this role - like an aircraft ejector seat system - warrants no corner-cutting.

My JSD MUST NOT FAIL....

You'll allow, I trust, some observations and questions which occur to me. If acceptable, I'll insert them at appropriate points - highlighted.

Originally Posted by Breaking Waves

1. Why would you feel the need to 'test' the soft shackle as they are quite a proven solution?

....I have never seen one tested in a 3 point load situation. My best guess is that it will be fine. But it is striking how often we discover something a bit unexpected when we test dyneema in a new application. There are often a few known unknowns but it is the unknown unknowns that frequently produce surprises. So, in critical applications, it is almost always worthwhile to test.

I entirely agree.

In this particular case, in static testing - it would be worth confirming that 'hoop loading' does not cause a problem, that having one of the thimbles bear either the loop or the noose does not cause a problem (it does not in 2 point loading, that is well known, but the strain angle will be different in 3 point loading),

Surely Don Jordan AND John Franta et al accept that ~20 degrees is fine?

and personally, I am skeptical of the use of the wire tie to close the loop (I think it will either slip or break or if neither of those it could create a stress riser) so that is worth testing.

It IS worth testing the use of a nylon cable-tie, not to 'close the loop' but to help hold it closed during unloaded phases - and I shall, but it is presently the best/simplest solution to the objection that I know. 'Occam's Razor' still applies.

In dynamic testing, one would want to know about wear/chafe from the thimbles, the behavior of the loop under cyclic loading (personally I don't think this is any sort of issue with a properly sized loop, we essentially see no accidental openings in 2 point loading applications) is worth looking at.

I presume this relates to the 'soft shackle' as shown in pics below. And I agree. I'll post pics of the outcomes when I return from some operational testing. Should I not come back, you'll know there was a problem....

And then in both static and dynamic cases - there is always the possibility of learning about some currently unknown unknowns. I guess it will be all ok, but on the other hand we might learn something new.

2. What is the 'more obvious textile way' (than the soft shackle) you refer to?

A multiple loop, with end-to-end bury, with a Dyneema chafe cover. Benz has talked about these in other threads. This is the highest strength (almost twice the strength of the soft shackle using the same amount of dyneema) most proven approach. It still is textile, and so is potentially vulnerable to some things, but eliminates the weaknesses of the loop/knot. However, it is permanent, I don't think that should be much of a problem unless you are planning to regularly remove your bridle legs from the rode (if for example, you might be planning to also use those logs for some other purpose).

Yes. Agreed...


3. You say this would not be your personal solution - what would be?

I like the solution Saltylass and Fixxty have shown. It is quite elegant - light, compact, no metal to clang around, strong, and well-proven. There is a small and well-defined weakness in that bridle connection (strop join), but that is very easy to compensate for with just one size bigger line at that point.

I agree it is elegant - yet, as far as I can determine the recognised weakness is NOT well-defined. Is it 5%, 15% or 50%....? Show me the data. 'Form Follows Function'....
What's more, it appears to be BOTH bridle legs secured to the rode by a doubled-up cinch hitch.... which would also pull at an angle of ~20 degrees. Show me the numbers....

And how do you compensate by injecting 'just one size bigger line'. Surely that needs bigger line throughout, or a cascade of cinch hitches....?

I have mentioned before if you want to do this in the most 'proven industrial' way, then using a delta plate is the solution. That unfortunately means a pretty large chunk of metal. If you want to spend a little money, you can get an engineer to FEA the delta plate and a machine shop to remove quite a bit of less stressed metal, and you can do it in Ti (I have personally done this for two high spec applications) or high tensile aluminum, all of which will make it elegant and lighter. This is perhaps the strongest and least vulnerable of any solution (which is why it is standard for heavy lifting) . . but it is still a decently sized chunk of metal.


I looked at that tidy idea, which is manufactured for arboriculture purposes, but the cost when Safety Factors were considered ruled it out - for me, for now.

For most of our 'yachting applications,' I think the zero metal strop is probably preferred - easier to handle and certainly strong enough.

If this relates to the 'strop bend' or 'cinch hitch', it is certainly easier to handle. 'Strong enough' depends on the ACTUAL losses due to the tight bend/poor D:d ratio.

For me, this is a crucial part of the argument. Some here hold that 1:1 is OK, and 1.5:1 is a bit more OK. That, unless I'm missing something, strongly contradicted by the industry sources I've cited above.

Show me the data, convince me, and I'll gladly chuck my thimbles in the bin!


4. Care to comment on the quotes about knots and 1:1 bends?

The engineering is really quite well established and there really is zero controversy about this (among those who understand the engineering).

Among my sins, I earned my crust as a flight test engineer. I'm not afraid of big words.

One needs to understand that there are two different cases here, and people sometimes get confused between them. Case one is a bend in a rope with two loaded/working ends - for example, a rope over a sheave. Case two is a bend inside a closed-loop (like a spliced loop).

In case one, the various bend ratio charts (like the HAMPIDJAN chart John F refers to) apply directly. They show that a 1:1 bend will weaken the rope locally by about 50%. That is clear and unambiguous. And we know from pull testing that knots will weaken Dyneema by 50-65% (depends on the knot and the particular flavor of Dyneema). That is also clear and unambiguous. Given that, the advice to avoid knots and 1:1 bends in a case one application is understandable because you are giving away a lot of strength. However, I will comment that the strength loss is well understood and if you have an application where you absolutely need a knot or a 1:1 then it is quite simple to adjust the rope strength to compensate - so it is just simply an engineering problem and not something evil.

Wholly OK with that so far.

In Case 2, a closed-loop (like a spliced loop), the local strength within the loop is 200% (roughly, a bit of complexity for a few percent about throat angle and hoop loading).

It is my understanding, from multiple sources I've peered at, that 'tested strength' comes in at about 160%, but is rather variable depending on the quality and style of the splice. That's the figure I've accepted in my arithmetic, so perhaps I have 'more in hand'. Kindly show me otherwise....

That is well proven and understood (I will note that John F originally did NOT understand this until Evans and Brion explained it to him, and Evans then did 3 series of tests to show that it was true and that his three theoretical counter explanations did not in fact apply). So, in this case, if you have a 1:1 bend inside the loop, it is a 50% reduction of a local 200% strength, which gives you in the end 100% strength (it is a bit less than this, like 95% typically because of the marginal complexities). This has been proven and tested very extensively (if you are curious there is the old SA thread where Evans did multiple test runs to demonstrate it to John F.).

I'll hunt for this, then query my tech sources in English Braids and Marlow Ropes ( they're handy for me )

So, in case 2 applications 1:1 bends are rather more acceptable (just upsize the rope by a few percent if you really need totally 100% spec strength) - generally, it is accepted that 1.5:1 bends are totally accepted here (there are industrial rope fittings that use 1.5:1 bends).

Sorry, 'rather more acceptable' and 'totally accepted' is to me a non sequitur. Call it a Simple Logical Fallacy if you like.

This is true no matter someone's hand waving about Dyneema compressive strength or scaling or dynamic action. I personally would still rather avoid a 'knot' inside a loop, because almost always there is a solution to avoid that ugliness. A strop hitch however does not have the great weaknesses of a normal 'knot' - it is a bit worse than a straight 1:1 bend ratio (it is a strength loss of around 15%, depending on a number of factor), and most commercial riggers will recommend you just do a simple interlinked 1:1 splice to splice if you can, but the strop is quite acceptable and well understood and you can easily upside the rope to compensate for its loss if it is the best solution for the application (it does prevent some wear/chafe that directly interlinked splices may experience). So, in case 2 bend ratios higher that 1.5:1 don't, in fact, add much strength,

I don't buy the above. It is not a matter of ADDING strength, but avoiding REMOVING an unknown lot of it by injudicious choice of connections.

As for 'most commercial riggers', I've yet to meet one who 'understands the engineering' or is even interested in the mechanics of a JSD in action - and I've asked a good handful.

and if the throat angle is high (which it has historically been in some thimbles which have been focused exclusively on pushing bend ratios up) then it can in the worse case in fact be weaker. I will comment that there is potential long-term value The 'well in thimbles reducing wear at the contact point, however, Dyneema is incredibly wear-resistant and this is not a huge issue for most of our yachting applications (it is a bigger issue in some commercial applications).

This is all pretty well-proven engineering and not controversial.....

Our man Don Jordan, an aviation engineer, recommended an angle between bridle legs of ~20 degrees. I've found no controversy over that. Optimum throat angles where commercially-designed, tested and industry-accepted thimbles are used are well understood. That's perhaps an issue with Low Friction Rings, but not an issue for here and now.

As for potential wear on the spliced loop fitted through and around the tubular thimbles, a sleeve of readily-available antichafe tubing will deal with that. For the sake of a few pennies, I've fitted such to my spliced-loops-in-thimbles.

Here are a couple of pics of the arrangement I'm putting together ( so far ). I'm perfectly willing to change it for the better. Convince me!





Rode-to-bridle connection showing soft shackle - pro built.
Also showing 20 degree angulation, and some spare thimbles.







Close-up showing reusable cable-tie securing throat-loop.
Planned antichafe tubing over soft shackle not yet fitted.


I'm very aware of the trap of 'confirmation bias' and hope we manage to swerve around this very human self-deception. I'll use all the help I can get.

[Seaworthy Lass]

Hi Oldbilbo

Loss of strength when joining or bending UHMWPE depends dramatically on whether this is done using an eye splice portion where the load is halved between the two legs, or in a straight line section. Loss of strength can essentially be halved in an eye splice section without compromising overall system strength.

We had a lengthy discussion a couple of years ago here on CF regarding the best method of bridle connection.

Following contributions from many members, some highly experienced with testing UHMWPE, I opted to use a simple “modified strop bend” for want of a better name. It is essentially a stop bend that is modified to treat the two bridle eyes as one unit.

The reasons for using this were numerous and included the following:

- There are no metal components that could result in chafe.

- The structure is simple, which I tend to think helps contribute to less loss in strength.

- There is no movement that could result in chafe as the load is transferred from one bridle leg to the other.

- Unlike the most common method of girth hitching the bridle eyes to the eye of the leader, there is no throat created anywhere using this means of attachment so the eye length is not critical. The eye just needs to be big enough to fit the cones through if you want to dismantle the section.

- It can easily be loosened after load is applied.

I used 72 x bury for the eye splices, lock stitched using one strand of 8mm Acera. The lock stitching technique was Samson’s.

Using this technique I did not think chafe protection was needed at this junction, but the bridle eyes at the boat end are covered by UHMWPE chafe guard which will provide protection where they contact the boat at the panama leads and double bollards.

CAUTION: This has not been tested.

These images show side and top views of the bridle’s Y junction.
The angle of the bridle legs will end up being shallower than shown. I just threw them over convenient winches to take the photo:

[Seaworthy Lass]

Originally Posted by oldbilbo

My JSD MUST NOT FAIL....
……
Here are a couple of pics of the arrangement I'm putting together ( so far ). I'm perfectly willing to change it for the better. Convince me!
…..

This is just a personal opinion, but the edges of the thimble create potential for chafe. Adding an anti chafe sleeve will simply offer another layer of protection, it will not prevent chafe.

Despite being a huge fan of soft shackles, I would not use one in this application. The cable tie is not foolproof. If it ends up rubbing on the metal of the thimble it could easily snap. Although I have not experienced a soft shackle opening inadvertently, but others have, and I think with the possible constant loading and unloading there is potential for this, resulting in instant failure of the drogue. If you proceed with the thimbles, why not substitute a doubled over loop for the soft shackle?

SWL

[oldbilbo]

Hello, Seaworthy Lass, and thanks for your continued contribution.

I've followed your reasoning above, and the reasoning in many past contributions on/around this subject. There is perhaps little I would quibble with, except where I suspect the occasional non sequitur or unjustified assumption. My background makes me quite sensitive to snuffling those out.

My hesitation and the springboard for me looking past the bare 'modified strop bend' approach is simply that I can find NO data on the strength - or REDUCTION in strength - using that means of attaching rode to bridle legs.

Our friend Breaking Waves indicates he shares the view that testing is paramount, and that 'empirical data is king'. He also warns us against the surprises of 'unknown unknowns'. You properly note 'CAUTION: this has not been tested'. I would very much like to see the results of some pro testing of that configuration.

You also rightly point to the potential for unexpected abrasion over the edges of the thimbles I've used. I suspect there will little or none. You also are hesitant about the efficacy of a nylon cable-tie to anull any potential for the arrangement opening in service. I am rather more optimistic.

I think we may have brought into focus an area which could benefit us all by some testing. We might perhaps persuade Drew Frye at Practical Sailor to tackle this for us, if we could adequately define what it is we want to test. Alternatively, I might be able to persuade someone at English Braids or even Marlow Ropes to do this.

What thinks the congregation?


Oh, BTW, could you clarify what you mean by 'substitute a doubled over loop'...? I can't envisage what you have in mind....

[Breaking Waves]

Originally Posted by oldbilbo

Convince me!

Hmmmm . . . I'm not selling anything, I have no dog in this show, and your solution is adequate for your vessel. So, i am not trying to convince anyone of anything. I am interested in trying to educate, but there is only so much leading of the horse to water that I am willing to do.

Surely Don Jordan AND John Franta et al accept that ~20 degrees is fine?

You are confusing throat angle and hoop loading. You get both in a spliced loop and they interact. In that case, for a spliced loop I can't speak for Jordan or Franta* but most would agree that 20 degrees at the throat is ok and 12 degrees better if you can achieve it. ^ note: some of John's early thimbles seemed to focus 'too highly' on the bend ratio and as a result had pretty high throat angles, I believe he has been 'correcting' this over time.

But with a soft shackle, you don't have a throat or a throat angle. There is no feature that is tearing against itself as a high angle in a splice does. Instead, you just have potentially higher loading caused by simple vector mechanics. Do note that you pretty always want to avoid loading a conventional metal shackle at three points And do please note my comment about unknown unknowns - I have never seen a soft shackle tested for 3 point loading - it is possible we could be surprised. You have rather well oversized your soft shackle, so, as I said probably well ok. It is not hard to get a test conducted.


It IS worth testing the use of a nylon cable-tie, not to 'close the loop' but to help hold it closed during unloaded phases - and I shall, but it is presently the best/simplest solution to the objection that I know.

Heavy rubber o rings were the original solution when soft shackles were first developed and people were concerned about the shaking loose. I would think them a better solution that your wire ties - as I say I expect the wire ties to either slip or break or create a stress riser - none of which tightish rubber o rings will do.

as far as I can determine the recognized weakness is NOT well-defined. Is it 5%, 15% or 50%....? Show me the data.

I have conducted testing which is consistent with Samson's published 'rule of thumb': quote from Samson page 6: "Ropes can be attached with a cow-hitch connection. This allows ropes to be disconnected without having to re-splice. However, this is a less efficient method and results in strength loss of approximately 15% for ropes of similar size" The 15% depends on rope construction, so is a ballpark. (Note: There is also I believe cow hitch tests in the old SA thread. Also consistent with this).
I don't know how much 'proof' you demand - but you can again get a test done yourself if you want to see it with your own eyes.

And how do you compensate by injecting 'just one size bigger line'. Surely that needs bigger line throughout, or a cascade of cinch hitches....?

The simplest solution would be to upsize the bridle lines and the first leg of the rode (most Dyneema series drogues are composed of multiples legs of decreasing size.). You could also insert local pieces but that would be more work. I might note that I personally prefer to add chafe covers into the strop join because it increases the bend ratio on the loaded 'core'.

For me, this is a crucial part of the argument. Some here hold that 1:1 is OK, and 1.5:1 is a bit more OK. That, unless I'm missing something, strongly contradicted by the industry sources I've cited above. Show me the data, convince me, and I'll gladly chuck my thimbles in the bin!

Well you are in fact missing the main point, that we are talking about a bend inside a spliced/closed loop, so the local starting strength is 200%. This is well accepted. Just for example, listening to the vid, When you asked John about D/d, I do not believe you specified a closed-loop. In any case, Evans published a whole series of tests about closed-loop 1:1 bends on the SA thread - the data is all there in public.


It is my understanding, from multiple sources I've peered at, that 'tested strength' comes in at about 160%, but is rather variable depending on the quality and style of the splice.

I'm not sure what you are on about here. Are you talking about the strength of diamond knot soft shackles? If you are talking about the strength of a long bury splices end loop - the local strength inside the loop is clearly 200% because you have exactly two strands holding the load. There are various factors then reducing that strength (the bend and hoop loading), but 200% is where you are starting from.


Sorry, 'rather more acceptable' and 'totally accepted' is to me a non sequitur. Call it a Simple Logical Fallacy if you like.

ok, you are just being pissy here I think. 1:1 removes a small about of strength - if the system is still above spec after that removed strength then phrase it however you want but any engineer would accept that system design. However, if your spec is extremely close to the 100% line strength that strength reduction could possibly put the system under spec, in that case, 1.5:1 bend will put you back to 100%, and again I don't know how you want to phrase that be any engineer would accept that system design.

As for 'most commercial riggers', I've yet to meet one who 'understands the engineering' or is even interested in the mechanics of a JSD in action.

I was talking about the basic principles of these connections. We have a rope connection here, not that unusual a one, bridles are used all over heavy lifting and towing and other commercial applications. So, I was commenting that the engineering of those sorts of connections are pretty well understood and time tested. As I commented what is not well tested is the use of the soft shackle in 3 point load with thimbles in a dynamic application.

As for potential wear on the spliced loop fitted through and around the tubular thimbles, a sleeve of readily-available antichafe tubing will deal with that. For the sake of a few pennies, I've fitted such to my spliced-loops-in-thimbles.

actually that is not a area of great wear - that is exactly why you use a thimble in a commercial application there to avoid the wear at the peak of the splice. This is one of the value of thimbles over bare splice to splice loops. I would also cover the soft shackle in your application since that is what is going to see the wear.

I am puzzled by your attitude here. You are using the soft shackle in an untested way (which is probably fine but is untested) while yelling all over about the strop hitch (which has more commercial experience behind it than the soft shackle - again note samson specifically calls it out in many of their technical papers as a commercial way to join ropes). And I am honestly not sure what you are trying to accomplish at this point - you have built a perfectly fine solution for your vessel.

If you just want to understand this better: (1) think it would be helpful in your mind to separate some things: the spliced loop case from the two ends case, and throat angle from hoop loads, and bend ratio from long-term wear. and (2) go look at all the public testing Evans did - that is the greatest body of public work on this available. There is much more knowledge but most of it is not fully public and transparent like that is.

............

[wsmurdoch]

Originally Posted by oldbilbo

What thinks the congregation?

A couple of years ago I posted this after pulling a bit of spectra with my genoa winches. The knot I called a square knot is the way I saw riggers at work link slings together. We seem to now be calling it a strop hitch.

https://www.cruisersforum.com/forums...ml#post2883224

Although my Jordan drogue is is nylon, I have been following the UHWPE Jordan threads and keeping my eyes open.

The climber boys have been testing webbing strops linked together, and in that case the knot efficiency is not 100%. They show failures in the knot in both dynamic and in static testing. Now, webbing is not rope, but...

https://www.blackdiamondequipment.co...ings-together/

...gives some inkling of what might be needed for thorough testing.

Of course, we have the case 1 and case 2 examples.