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Old 15-05-2019, 11:48   #451
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Re: Stealth mode - New Generation Ropes

A little off topic, but I thought I had sorted buying Acera Amundsen directly from Timms via Peter Bernat. After a number of emails back and forth, he’s just confirmed that they cannot sell me the relatively short lengths that I requested (for our JSD) as it is not cost effective for them (I requested 14mm x 60m, 12mm x 51m, 10mm x 35m and 8mm x 44m). Sigh.

Does anyone have a contact or reference to a store that will sell me Acera and ship to NZ? I really envy the Europe-based folks for their access to fishery suppliers and such that just don’t seem to have any online sales capabilities.
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Old 15-05-2019, 12:23   #452
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Re: Stealth mode - New Generation Ropes

have you tried a stocking chandlery, which sells by the m, and asked if they will ship to you?

like perhaps these guys https://www.seagearmarine.com/acera-...en-per-ft.html
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Old 15-05-2019, 13:02   #453
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Re: Stealth mode - New Generation Ropes

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One more knot, in case someone is interested in using only one piece of rope, with only one working end to be tied, spliced, whipped or stitched somewhere somehow.
FYI. This knot seems to be ABOK #1097.
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Old 15-05-2019, 20:09   #454
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Re: Stealth mode - New Generation Ropes

Regarding the connection between bridles and leader and between the rode segments, I’m not sure if this article has already been referenced but if not some interesting testing about connections between ropes https://www.wilhelmsen.com/marine-pr...-single-tails/.

It is about connecting stretchy rope to no stretch rope, but I‘m not sure whether the relative figures of the connection strengths are affected by that property.

Bottom line, cow hitch is slightly less strong (0.93) than eye to eye connection (0.95). Best connection is with a hard link (0.96). Given that we can easily upgrade the strength of the rope we use there appears to be no problem to use cow hitches. Note in the test connections photos that the tested cow hitch is ‘undressed’.

So the remaining issue, not tested in this example, is the loss of strength to bending and assymetrical loading at the bridle/leader connection. The proposal to only hitch the leader seems to solve that issue.
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Old 16-05-2019, 00:49   #455
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Re: Stealth mode - New Generation Ropes

@fxykty: odd as it may sound, you might try Fosters in Auckland, see if they can get what you need for your.

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Old 16-05-2019, 02:17   #456
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Re: Stealth mode - New Generation Ropes

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The sheet lead system which I made for my blade jib, when I first acquired that sail some 5 years ago, uses several low friction rings on each side, to create a purchase system for adjustment of the sheet lead as a substitute for a track.


For v1.0 of this system, I made the necessary strops using whipping to bind the legs of the strops together to retain the eye. The whipping kept coming apart, and I couldn't understand it -- at first I thought that I was not tying it correctly.



As usual I discussed the problem with my friends on here, and SWL jumped in and figured it out -- the throat tearing forces were pulling the whipping apart.


So eventually in the course of discussion we came up with a way to weave the whipping so that the legs are not pulled together, or not much, and all those strops which I re-made five years ago with the new weave are still going strong today, after 15,000 miles or whatever of ocean sailing.


But SWL got so fascinated with throat-tearing forces in spliced eyes that she invented her famous Bullseye strop, which is depicted in her avatar, which is a leap forward, which captures the ring without throat tearing at all. I'm waiting for her book on knots and splices and rope theory to come out -- I'll be first in line to buy it.
While I believe that people knew about everything about ropes and knots 100 years ago, and that ABOK collected much of this tradition for us to learn, we now have all kind of new ropes, rings and other techniques, and we are in some sense living a new golden age of innovation. New studies and new improved solutions are thus greatly needed and very welcome.
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Old 16-05-2019, 03:29   #457
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Re: Stealth mode - New Generation Ropes

Fxykty,

I'm sorry to have given you a bum steer on the Timms and Acera. I was not aware that Timms had decided to apply minimum order quantities to their products. That was not the situation when I last communicated with them.

It seems they are hard pressed to fulfill shipping orders, and I can confirm that they now apply a 300 meter MOQ on the ropes.

What a shame. 😡

Ok, now who do we buy from, and why are there no Timms distributors?

Maybe we can band together and put in a group order, then chop it up to the lengths we each need for JSD's, lazy jacks, halyards, etc.

Anyone interested?


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Old 16-05-2019, 03:41   #458
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Re: Stealth mode - New Generation Ropes

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While I believe that people knew about everything about ropes and knots 100 years ago, and that ABOK collected much of this tradition for us to learn, we now have all kind of new ropes, rings and other techniques, and we are in some sense living a new golden age of innovation. New studies and new improved solutions are thus greatly needed and very welcome.

I think that SWL knows better and can explain better than I can, but the possibilities of what you can do with a piece of rope are probably unlimited, or limited only by human imagination. Even without the new materials and rings and so forth.


There are more possible chess games than there are atoms in the known universe -- that's on just 64 squares with 32 pieces.
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Old 16-05-2019, 04:34   #459
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Re: Stealth mode - New Generation Ropes

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Originally Posted by fxykty View Post
A little off topic, but I thought I had sorted buying Acera Amundsen directly from Timms via Peter Bernat. After a number of emails back and forth, he’s just confirmed that they cannot sell me the relatively short lengths that I requested (for our JSD) as it is not cost effective for them (I requested 14mm x 60m, 12mm x 51m, 10mm x 35m and 8mm x 44m). Sigh.
Oh, that explains a lot!
I wish he let me know this three weeks ago when I first emailed him and I would have tried sourcing it elsewhere. He just left me hanging .

For anyone in Europe, Southern Ropes Stealth Super-12 is apparently available through some chandleries, but I don’t know how extensively.

SWL
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Old 16-05-2019, 05:02   #460
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Re: Stealth mode - New Generation Ropes

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Lots of great information in the posts. Thanks to everyone.

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Originally Posted by Seaworthy Lass View Post
Spliced eye loops if well constructed (long bury with the tail tapered gradually over the last 1/3) give close to line strength if the eye passes around an object greater than or equal to in diameter than the line diameter and if the throat angle of the eye is low.
That sounds like a good rule for this kind of work. Once you make that good long splice, you will have two lines that can share the load (and you can in principle even use 50% strength knots). Are you planning to use a heavier line for the bridle, or would two parallel lines (a loop) of the same rope do? Or are you using a heavier line just to make the diameter larger, to help the spliced loop of the primary drogue line?
I am going with eye splices at the ends of the bridles, rather than making them loops. I think there is little additional benefit making them loops of the same diameter given the loss of strength at the junction. I still plan to connect the bridle legs and the leader using the modified strop bend shown below.

I bought 12 mm Acera for the bridle, which has a MBS 25% higher than that suggested by Jordan. After all this discussion I was going to bump it up to 14 mm, but I am finding this hard to source. So for now I will just make it up in 12 mm with chafe protection.


Quote:
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I'd be interested in trying some whipping at the base of the eye (if the angle gets big). That should eliminate some of the forces tearing the loop apart. I'm not sure if the whipping should be made tight or not so much (to better avoid uneven loading of the fibres).
It doesn’t actually eliminate any of the forces, it will just shift them to the circumference of the throat. I don’t know how much better it is having the whipping cutting into the line, as opposed to the splice being forced apart internally. The load is apparently distributed over the first few turns of the whipping, but I don’t like the thought of that cutting into UHMWPE with the loads the bridle is subject to.

I would far prefer to simply make the eye long and therefore avoid this problem. In the scheme of things very little extra rope is needed for this.

SWL

Using the modified strop bend, eye length is actually not an issue (the legs within the eyesplice are not spread apart at all), which eliminates one source of error for anyone making up this drogue in UHMWPE:
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Unveiling Bullseye strops for low friction rings
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Old 16-05-2019, 05:40   #461
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Re: Stealth mode - New Generation Ropes

After ten days to think about it, the above solution that WSMurdoch proposed is simply looking better and better to me. I feel comfortable with it in this application. I need to stress though that it is untested. I have never seen a bridle connected this way.

SWL

PS Bill, I have tried pressing the “Thanks” button again on your last post, but the system won’t accept two lots of thanks on one post. Anyway, thanks for persisting with thinking about solutions. I knew if we put our thinking caps on, something good would come out of it .
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Old 16-05-2019, 06:08   #462
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Re: Stealth mode - New Generation Ropes

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Attachment 192094
breaking wave

Thanks!! Good answers.


As for the stitching, many people overlook the fact that climbing slings are loops, largely for the reasons you gave. Much easier to get full strength than with two eyes. The lifting sling folks know this too.
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Old 16-05-2019, 06:18   #463
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Re: Stealth mode - New Generation Ropes

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I have never seen a bridle connected this way.
I've seen it on multipart lifting bridles (with like 4 bridle arms to the different corners of a container) - where a string of 4 or more connections side by side is awkward in the loop. I've not seen it used with just two bridle arms but should be fine. Very simple and easy

However, I personally will put a very strong gasket in the connection. The reason is to keep the 'compression' off the permanent pieces of the drogue (the eyes of the rode and bridle arms) and on a simple easy to replace extremely strong piece.

Probably this is splitting hairs, and adding 'unnecessary' strength to a component which is not the weak link. But, it is a simple step which addresses a known engineering challenge in the system. I personally don't see any downside to adding the gasket.

Quote:
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As for the stitching, many people overlook the fact that climbing slings are loops, largely for the reasons you gave. Much easier to get full strength than with two eyes. The lifting sling folks know this too.
Do the climbers all use bar tacks on their slings - I think they usually do but don't know if anyone has tried anything else? Many of the high load lifting slings use alternate patterns, which I believe come from those old parachute webbing testing/research. I don't really know much about it, don't know how much stronger they are (if at all, and would probably want a computer controlled sewing machine (which I don't have access to) to make them (some are pretty elaborate) so I could get repeatability.

I really wish more of the commercial testing results were published. There is a ton of knowledge 'locked away'. It is a bit frustrating when trying to discuss/debate alternatives and makes self-education more difficult than it needs to be.
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Old 16-05-2019, 06:34   #464
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Re: Stealth mode - New Generation Ropes

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I've seen it on multipart lifting bridles (with like 4 bridle arms to the different corners of a container). Should be fine. Very simple and easy

However, I personally will put a very strong gasket in the connection. The reason is to keep the 'compression' off the permanent pieces of the drogue (the eys of the rode and bridle arms) and on a simple easy to replace extremely strong piece.

Probably this is splitting hairs, and adding 'unnecessary' strength to a component which is not the weak link. But, it is a simple step which addresses a known engineering challenge in the system. I personally don't see any downside to adding the gasket.
Thanks for the feedback. The simplicity is a big factor in the appeal of this solution. It is not a complex bend.

I was thinking of making the first section of the leader two sections, the first short and therefore replaceable with the bridle. It is sensible to make this short bit a loop.

I am in favour of replacing the bridle and this first bit of the leader after x hours of use, particularly while the use of UHMWPE for this drogue is largely untested. Chafe can be inspected for, but weakness due to compression and bending fatigue cannot.

I don’t know what waters we will find ourselves in, but in certain areas multiple uses of the drogue are needed each season. I may be a bit of an adrenaline junkie, but I do like to do things as safely as possible.

SWL
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Old 16-05-2019, 06:49   #465
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Re: Stealth mode - New Generation Ropes

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in certain areas multiple uses of the drogue are needed each season.
There are two use cases (to simplify).

The vast majority of the deployments you will only have like max 10% design load on the drogue. In that case (I believe), you will primarily have retrieval damage issues and cone wear to be concerned with, but also a possibility for chafe and cutting while it's out if the configuration/fairleads/etc have any unanticipated drawbacks. These should be essentially eliminated if you inspect and modify after early uses.

I personally liked to use a single element drogue in most of these situations rather than the series both because it is easier to recover but also to keep wear off the cones. But you do need to make a conservative assessment of the weather situation and use the series if there is any significant probability of the second sort of case ....

Very Very occasionally you will have an actual large breaking wave strike. This will impose loads closer to the design loads. This will cause a different sort of damage, which is harder to inspect because it is internal to the line. Replacement of the focused points/components after every single incident of true large/serious breaking wave strike would I think be prudent.

Edit: on reflection, that Samson article on tow lines suggests there can be compression damage even at quite low percent of ultimate loading. I’m going to dig into that a bit as I have not seen that elsewhere. But if so, it could create internal damage even in the 10% case. I’m a bit skeptical but this is definitely testable, worth exploring.
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