Stealth mode - New Generation Ropes

[Dockhead]

Originally Posted by Seaworthy Lass

Hi guys
Sorry for the delay replying. I have been offline most of the day.

The angle I am talking about is not the angle the bridle makes with the leader.

It is not just a case of looping the three legs together. The same problem would exist. It is an issue with the throat angle of the eye of the leader.

Below is a diagram of what I think will occur when the load is distributed equally between the legs of the bridle. The eye of the leader will form an equilateral triangle. It matters not if the eyes of the legs of the bridle are cow hitched or spliced on. There will be a tearing force at the throat of the eye of the leader. Unlike the usual tearing forces at this point when load is applied to the peak of the loop, it does not matter how big the eye of the loop is (the 60° geometry will always exist).

With a 60° throat the tearing force is 29% of the total load. I think this will fairly easily rip the base of the throat of the leader apart and the entire drogue will be lost.

SWL

PS If someone could please check the formula it would be good. My trig skills are OK, but physics is not my forte .

Another comment to this --


The angles will be quite different, with 2.5:1 -- the throat angle will be 22.5 degrees, not 60 degrees.



What you show is an equilateral triangle, which you will get if the bridle legs are the same length as the distance between the cleats, which is surely way too short.

[thinwater]

Throat Angle:


I'm guessing on this, but from everything I understand, in the worst case you are mostly likely to see the peak load at an angle to one side. As the boat accelerates down the wave, the bow will root in and it will turn. Thus, the load is on one leg and there is no spreading force.


One reason this is the worst case is that the wave is striking the boat, to some extent, from the side. There is more exposed area. I doubt a worst case strike is ever from exactly astern.


If you want to fight the spreading force on a slice, a heavy seizing can be speced to carry it. I've tested this approach. It works. Every eye on a thimble faces this, though somewhat less.



Just guessing.

[Dockhead]

Originally Posted by Fi2010

. . . You feel strongly about your product. So do we.. .

"My product"? I'm not selling anything, and have no interest, financial or otherwise, in any drag devices, or any other marine product. I'm not even a journalist. I'm just a cruiser, like most of the rest of us on here, interesting in expanding my knowledge and finding flaws in my thinking or practice, and sharing whatever I know which could be useful to others. Don't compare yourself to me -- we come at this from totally different perspectives.



If you have concrete, useful information about bridle lengths, or real life problems in specific concrete cases about any kind of drag device, or if you have specific disagreements with anything anyone else has said, this is interesting and useful.


However, vague references to problems in competing systems made by a vendor interesting in selling a product, without any engineering arguments or even real life anecdotes, comes off as salesmanship by slagging off the competition.



This is really not the place for that. We have a bad history of anchor manufacturers and refrigeration companies (to name two) coming on here and trying to sell their products and tear down their competition by pretending to participate in discussions on the same level as the rest of us while pursuing very different goals. The problem is that the motivation is different, from the rest of us. It's great to have people on here who have actual professional experience, unlike most of the rest of us -- potentially there is a lot of value in that. That's why we, in theory, welcome vendors to participate in our discussions. But the commercial claws need to pulled right in, and taped over with duct tape.



Otherwise, you will get an opposite result, from what you intend. The membership here is very sensitive to this kind of behavior. I think the original Rocna company was actually ruined as a result of backlash from this kind of salesmanship by Craig Smith, the son of the founder, on this forum -- a case worth studying.

[Seaworthy Lass]

Originally Posted by Dockhead

"My product"? I'm not selling anything, and have no interest, financial or otherwise, in any drag devices, or any other marine product. I'm not even a journalist. I'm just a cruiser, like most of the rest of us on here, interesting in expanding my knowledge and finding flaws in my thinking or practice, and sharing whatever I know which could be useful to others. Don't compare yourself to me -- we come at this from totally different perspectives.



If you have concrete, useful information about bridle lengths, or real life problems in specific concrete cases about any kind of drag device, or if you have specific disagreements with anything anyone else has said, this is interesting and useful.


However, vague references to problems in competing systems made by a vendor interesting in selling a product, without any engineering arguments or even real life anecdotes, comes off as salesmanship by slagging off the competition.



This is really not the place for that. We have a bad history of anchor manufacturers and refrigeration companies (to name two) coming on here and trying to sell their products and tear down their competition by pretending to participate in discussions on the same level as the rest of us while pursuing very different goals. The problem is that the motivation is different, from the rest of us. It's great to have people on here who have actual professional experience, unlike most of the rest of us -- potentially there is a lot of value in that. That's why we, in theory, welcome vendors to participate in our discussions. But the commercial claws need to pulled right in, and taped over with duct tape.



Otherwise, you will get an opposite result, from what you intend. The membership here is very sensitive to this kind of behavior. I think the original Rocna company was actually ruined as a result of backlash from this kind of salesmanship by Craig Smith, the son of the founder, on this forum -- a case worth studying.

To put it simply .
The marketing of the Shark drogue has been extremely offputting. Diametrically opposed to the desired effect. I have been highly put off purchasing one, not encouraged.

SWL

[Fi2010]

Your posts demonstrate you favor the JSD. That’s great! It all boils down to personal preference as we’ve posted numerous times. We sell the JSD as well as other competing equipment so the subject is rather mute.

We’ve been supplying some great technical advice for sailors to consider regardless of what drag device they choose to use. We believe the information can improve performance. However, if you omit pertinent details about any drag device, claim unsubstantiated bias, or post misleading statements about our company or associates we'll set the record straight.

[conachair]

Originally Posted by Seaworthy Lass

To put it simply .
The marketing of the Shark drogue has been extremely offputting. Diametrically opposed to the desired effect. I have been highly put off purchasing one, not encouraged.

SWL

And another.

[Breaking Waves]

Originally Posted by Seaworthy Lass

>>The angle I am talking about is not the angle the bridle makes with the >>leader. It is an issue with the throat angle of the eye of the leader.

Yes, I, in fact, do actually understand exactly what you are talking about - which is why I quoted the benchmarks for spliced throat angle to start off my post.

>>Below is a diagram of what I think will occur when the load is distributed >>equally between the legs of the bridle.

So, no, that is in fact not what will happen. You seem to like pictures, so I took 3 with three different 'bridle lengths'. You can do your own experimentation. There is of course physics to explain and predict and calculate this. (the blue line is the rode drogue with loop, the while lines are the bridle arms)

Short bridle:


Medium bridle:


Long Bridle:




As to all the various discussion about 'shock loading'; my experience and the basic theory behind the series is that it takes loading progressively. It is the least shock loading drag device you can use. I believe F's concerns about shock loading apply to para anchors and other big single elements but are really generally not at all a real world issue with the series.

Thinwater's 'yaw shock loading' is interesting - you yaw no matter what (again within the reasonable range) bridle length you use, and I can't say I felt any difference in the individual arm pulse loading. And if I do some math taking a boat with 10' transom and a short bridle with 45-degree angle compared to same boat with a long bridle and a 10 degree angle . . . and then I yaw the boat 30 degrees both bridles 'loose arm' develop around 4' of slack which would be the 'opportunity for shock loading' and in fact if the shorter bridle corrects the yaw more quickly (as is argued) then the shorter bridle might create more shock loading (because more acceleration). Yea, its more complex that that, and I we could make other arguments (like the shorter bridle might yaw to a smaller angle). But I don't find a convincing case either in my own experience or in the math that there is going to be a huge change in shock loading

As to the 'longer bridle creates less steering impulse'; it is, of course, true but in my experience (I have used series in storm force with 'regular and 'long' bridles) assuming you keep the bridle within 'reasonable, close to standard' parameters, the effect with a jsd is not (at least by me) all that noticeable/significant. I personally prefer a longer bridle because I have seen a good length of the rode (and its cones) bridge to a steep wave behind and lift out of the water. I don't see much point in having cones lifting out of the water, and the longer bridle helps minimizes that effect.

-----------

[BigBeakie]

SWL,

"I have spent the day visiting a couple of fishing chandleries in the Netherlands. Gear is available that is not seen in yachting chandleries. Stainless steel or steel Crosby loop options do not look good."

Could you expand on why the closed & gussetted stainless thimble & shackle is not the way to go? Weight, crevice corrosion, shackle not moused ??

What problems do you see in this approach for the (A) bridle to ship attachment, and (B) the bridle legs to JSD leader attachment?

[fxykty]

Oh boy, I’m getting very confused about putting together our JSD drogue. I guess I’ll just order the lengths I need and keep connecting options open. I’ve emailed Peter at Timms and he’s been very responsive, so thanks for the contact.

• Connecting the leader, middle and tail segments together seems relatively clear - choice seems to be either long splices or cow hitched spliced eyes. With the cow hitch option, I suppose it’s the smaller diameter eye that gets dressed into the cow hitch? Comments on either option?

• Connecting bridle ends to boat and tail to chain (or other weight) - choice seems to be either soft eyes cow hitched to their respective mounting structure, or eyes with hard thimbles and shackled traditionally. Which option to choose seems to be up to whether you want to avoid metal in the rode or not.

• The big problem seems to be connecting the bridle legs to the leader. Ignoring the length of each bridle leg (for now, sticking with the 2.5 x chain plate beam formula, which for our cat works out to 17.5m each), the first decision is whether one line for the bridle with a spliced eye in the middle of the bridle line or two bridle lines? Comments either way?

• The second decision is how to connect the two bridle legs to the leader. This isn’t as confusing if the bridle is a single line with a eye in the middle, as that seems to a simple cow hitch with the leader’s eye. But with two bridle lines, hmmm. The relatively long 2.5 x beam bridles seem to keep the angle between them relatively small, but I guess there will still be some movement. As an additional loop in the same diameter will need to be quite long, the options seem to be a SS ring (and everything cow hitching to that - hmmm, can’t do that if cow hitching the boat ends of the bridles to their mounting points) or a multiple strand loop using thinner line - how would that be done?

Awaiting further revelations from the wise ones on this thread.

Thanks so much for your contributions.

[andrzej0nl1ne]

As a concept, would this approach work? The eye is aluminum from colligo marine, used with their dux based standing rigging. The schacle is demonstrative as are the 2 bridle eyes.

[Seaworthy Lass]

Originally Posted by Dockhead

Another comment to this --

The angles will be quite different, with 2.5:1 -- the throat angle will be 22.5 degrees, not 60 degrees.

What you show is an equilateral triangle, which you will get if the bridle legs are the same length as the distance between the cleats, which is surely way too short.

Yes, you are right. I had a senior’s moment and forgot the bridle was 2.5 x the distance between the connection points. I was for some reason focussed on equal legs.

Won’t that make the angle 23° though?

So the tearing force at the throat would be roughly (50 x tan 23/2 °)% = 10% of the total load.

Not as dramatic, but still a lot pulling apart the splice.

Originally Posted by Breaking Waves

Yes, I, in fact, do actually understand exactly what you are talking about - which is why I quoted the benchmarks for spliced throat angle to start off my post.

So, no, that is in fact not what will happen. You seem to like pictures, so I took 3 with three different 'bridle lengths'. You can do your own experimentation. There is of course physics to explain and predict and calculate this. (the blue line is the rode drogue with loop, the while lines are the bridle arms)

Thanks. I do like pictures .

The penny dropped when Dockhead reminded me the bridle length was 2.5 x the distance between the connection points.

SWL

[Breaking Waves]

Originally Posted by fxykty

Awaiting further revelations from the wise ones on this thread.

Definitely not wise. I probably would not have spent so much of my time at sea if I was.

But I do like to follow the combination of empirical evidence and plus engineering.

In the case of the bridle rode attachment #1 I am not aware of any cases of failure there except when a knot was improperly used. We do NOT have an empirical problem here to solve. #2 SWL raised a valid engineering concern about throat angle, however either sufficiently long/low angle bridle arms (eg including the standard Jorden design recommendations) and/or SWL's super strong loop connector will eliminate this concern while keeping all the benefits of a full textile solution.

I have previously simply used the recommended cow hitched loops, which have worked fine. However, I happen to quite like SWL's super strong loop suggestion. It is easy to make and improves that link in the system and I see zero downsides to it. Done correctly that loop link will never ever be a weak point. That is a nice thing to be able to say with a system which is designed to take huge peak loads and can save your life.

Originally Posted by Seaworthy Lass

Won’t that make the angle 23° though?

SWL

Actually not, actually rather smaller than that. In the calculation, I used some posts above (which DH is referencing) I used a severe short cut formula which produces 'not more than' results. It was enough to show that the typical bridle lengths certainly meet the normal throat angle benchmarks. But actually, if you properly calculate the angle it will turn out to be quite a bit smaller than this. If you have a CAD program and or can measure angles some way you can see this quite clearly in the picture sequence. Actually, if you just look at the 3rd photo you will see there is essentially zero throat angle, much less than the short cut calculation suggests. This is a result of the fact that the bridle arms together share the load, so each are 1/2 the load on the road (not exactly because of the angle, but definitely way less than the main rode load with reasonable bridle lengths) which means they are pinched together by the pull from the main rode. There is a more complex formula to calculate the angles correctly/exactly, but the one I used is typically used because it is easy and has a built-in safety factor.

That all said, I like your loop idea, and I can't see any drawbacks to it so long as it is made properly hugely strong, so I would use that 'the next time'.

[Seaworthy Lass]

Originally Posted by BigBeakie

SWL,

"I have spent the day visiting a couple of fishing chandleries in the Netherlands. Gear is available that is not seen in yachting chandleries. Stainless steel or steel Crosby loop options do not look good."

Could you expand on why the closed & gussetted stainless thimble & shackle is not the way to go? Weight, crevice corrosion, shackle not moused ??

What problems do you see in this approach for the (A) bridle to ship attachment, and (B) the bridle legs to JSD leader attachment?

I have attached the photo of the Crosby ring I found. This was 7/8” and the smallest I found. It seemed to weigh a ton. The bridle and leader are just lightweight Acera. When the load was temporarily off the drogue, rightly or wrongly I could just imagine the ring briefly causing the bridle to drop and possibly tangle with the rudder.

Big Crosby shackles were also available (up to 17 ton working load) but the geometry of those didn’t look right for a three point connection.

I found smaller SS rings, but the quality of weld is unknown. I would not be happy relying on those, I would far prefer a soft loop.

SWL

[thinwater]

Originally Posted by Seaworthy Lass

I have attached the photo of the Crosby ring I found. This was 7/8” and the smallest I found. It seemed to weigh a ton. The bridle and leader are just lightweight Acera. When the load was temporarily off the drogue, rightly or wrongly I could just imagine the ring briefly causing the bridle to drop and possibly tangle with the rudder.

Big Crosby shackles were also available (up to 17 ton working load) but the geometry of those didn’t look right for a three point connection.

I found smaller SS rings, but the quality of weld is unknown. I would not be happy relying on those, I would far prefer a soft loop.

SWL

So splice a grommet in Dyneema? Not difficult.


But I think a simpler solution is a bridle angle <90 degrees and a strong throat seizing. The throat angle on the splice is no greater than a thimble.

[Seaworthy Lass]

Originally Posted by thinwater

.....
But I think a simpler solution is a bridle angle <90 degrees and a strong throat seizing. The throat angle on the splice is no greater than a thimble.

As Breaking Waves has pointed out, calculations for determining the exact throat angle are complicated and will be less than the simple calculation giving 23°, but I don’t have a good feel for how much less. I still think the angle may pose a problem regarding the tearing force at the throat.

Samson (who I have found publish excellent advice on all things related to ropes, including the best splicing instructions I have ever found online) recommend a throat proportion of 3:1 and preferably 5:1, as written in the diagram below from their pdf.

This means Samson are recommending the throat angle is preferably less than 13°.

By the way, I have never seen thimbles with a 5:1 ratio. I would be wary of thimbles in this application as well, even if there is no risk of chafe.

SWL