Drogue Failures

[Dockhead]

Originally Posted by oldbilbo

No vehemence. It is simple refutation of largely unsupported opinion based on assumed 'non sequiturs'. Show me the links to the data. I'll draw my own conclusions. If they differ from yours, that's showbiz.


And perhaps what is not understood is that emotion in social media posts - such as vehemence - does not communicate well, if at all, from a keyboard. That is imagined, then erroneously projected into the text. Some might call the application of scepticism in the absence of acceptable data to be an example of 'peer review'......

Nothing was refuted; just a bunch of invective. And rudeness communicates very well indeed via keyboards.

Originally Posted by oldbilbo

That is a supposition, a jump too far, a 'non sequitur'. It does not necessarily follow. Show me the experimental data.

Not a non-sequitur to anyone who knows the one most basic fact about the strength of cordage -- namely that cordage loses strength when bent, as a function of the radius of the bend.



The logic is very simple --



1. Any loop of single braid dyneema will have full strength of the cordage at a bend radius of somewhat more than 1:1. Link to information about that was supplied. [It can actually be somewhat more complicated than that -- the strength will be reduced as a function of the sharpest part of non-ideally round bend.]



2. Joined eyes lead the loops around two legs of the other cordage, improving the bend radius, providing something like 1:2 for two eyes in equal size cordage, which even allowing for imperfect roundness of the bend, should make the loop comfortably stronger than the cordage.


3. Joined eyes between cordage of different sizes will be even stronger, as a function of the strength of the smaller cordage, because the bend radius will be even better around the two legs of larger cordage.





There is a ton of information about this in the internet, so you can do your own research, and if you find a flaw in what I have presented here, I will be very grateful to hear about it, especially if you present it in a factual, polite, and respectful manner.


Here is just one example of a test of splices and loops in single braid dyneema:

https://www.youtube.com/watch?v=z5_L...ature=youtu.be

These are short splices and 1:1 loops, so much worse than the way you would put together a JSD with joined eyes. Nevertheless, the splices and loops are stronger than the cordage, which is consistent with my experience.

Originally Posted by oldbilbo

. . . How much do we take on blind trust, and how much do we take on inspection?

Parachutists pack their own chutes. When I go up the mast, or hang on a drogue in a storm, I only do it on ropes I spliced myself.

[Dockhead]

Originally Posted by oldbilbo

Here's something else which popped up on a Pinterest page....




I like the creativity....

http://www.cruisersforum.com/forums/...gs-169764.html

[conachair]

Here is just one example of a test of splices and loops in single braid dyneema:

And more here >


https://web.archive.org/web/20160318...s.com/load.htm

[Dockhead]

Originally Posted by Paul L

Dockhead
I'm not clear what your loop attachment is for the multiple sections of the drogue. Are these large loops where you pass the other tail and all the cones through the loop? How is this different than a cow hitch?

That's a very good question. The Sampson Ropes manual actually refers to these joined eyes as a "cow hitch". But I really wouldn't call it that -- a cow hitch bends the cordage differently:





That's a cow hitch, and you can see how it's different. Source: https://sailrite.wordpress.com/tag/j...series-drogue/


Directions here:







From: https://www.sailrite.com/PDF/Drogue-Instructions.pdf


But I don't like this construction, even if it is surely strong enough. It's just inelegant and no trouble at all to double those bend radii.





And yes -- for joined eyes, you make long loops -- longer loops are better for strength anyway, because of the throat angle -- and just pass the whole tail together with the cones through the loop in the other section. Actually you have to pass BOTH ends of BOTH sections, through each other, to do joined eyes. This is not a big deal. I'm sorry I'm not on my boat, or I would show you my drogue.

[oldbilbo]

There's an intriguing discussion somewhere else within these pages, that I cannot find at the moment, around uses and nomenclature for the 'dyneema strop with a low friction ring'. Perhaps someone might 'move' this there, if thought appropriate.


The contributor 'Seaworthy Lass' sought suggestions for a name reflecting her invention of a new form of strop. Might I offer 'Lattice Strop'....?


Also, there was discussion of the weakness of a cow hitch securing such a strop to a deck eye, due to 'compression of the fibres'. I'm not clear where exactly the relevant fibres are compressed to disadvantage, but might it be worth considering the use of a Prusik Knot Instead of the Cow Hitch?



Prusik by oldbilbo, on Flickr

[thinwater]

Originally Posted by deluxe68

Did Galerider go out of business? I was planning on buying one this year, now I am looking into the Fiorentino Shark. Any unbiased reviews on this brand?

No, Landfall Navigation has another manufacture set up. No changes in construction.

[thinwater]

Morgan's Cloud / AAC just reported on the probable cause of Goodall's drogue failure.


Sorry, no spoilers. It is behind his paywall.


https://www.morganscloud.com/

[Fi2010]

Originally Posted by thinwater

The loss of Suzie Goodall's boat in the Golden Globe Race due, in part, to drogue failure, has generated a few threads. Some time ago a fella ran a data base (I'll leave the name out) based on real world experiences, but it has become a bit dated.

I'm not going to theorize about Goodall's failure yet. I'm hoping more information will arise, though perhaps it sunk with the boat and Goodall surely had her hands full.

What actual failures do we know of? I've been really brief, and I know that, so don't nit pick. Just add usable info. Some will say they are useless, which they probably are for bigger boats. This is NOT one size fits all.

• Chafe. Probably the most common. Can happen anywhere; attachment points, over the rail, steering gear (numerous cases), thimbles, etc. Easy to under estimate, since we don't get much practice rigging gear under such strain. Seems to be more of a problem with sea anchors and JSDs (more stress).
• JSD cone fraying and failure. During long, extreme storms, or multiple storms, light weight cones can disintegrate. However, the failures are gradual and I don't recall any leading to actual trouble.
• Gale Rider cable ring failure. Several cases. Only a minor effect on performance.
• Sea anchor rode overload. Whether heating or simply overloaded, I think these are sometimes under-speced (they should logically be larger than anchor rodes, but often are not).
• Sea anchor, ride problems. Not all boats can ride to a sea anchor, and sizing/rigging can be tricky.
• Single element drogues snapping forward due to steep waves and nylon rode recoil.
• Too much rode stretch. While required with chutes, it can allow the boat to go backwards. With drogues, it sometimes allowed a little surfing to start. Should JSD and single element rodes by reduced stretch?

Fire away!

The Drag Device Database by Victor Shane has many useful testimonials about drag devices. The mishaps you list are in the book. Although, most of the DDDB is about the successful use of these safety devices.

Our testing demonstrates shock loading is likely the primary cause for chafe and rode breakage. However, if there’s a design issue or if cheap parts are used to build a device, then equipment can fail.

As simple as it is, the big secret is to maintain “Constant Rode Tension” with your storm drogue or para-anchor. “Constant Rode Tension” can be achieved with rode adjustment, proper weight placement, or by decreasing or increasing vessel speed via motor or sail. This technique works whether or not you choose a head to wind, hove-to, or forereach position. Follow the published “Constant Rode Tension” formula and you should see improved results using any brand of drag device. The formula is available on the internet.

The test video in post #11 by Kolchac demonstrates how weight attachment, one simple solution, improved the performance of the storm drogues. It’s important to mention that many manufacturers do not recommend weight attachment to their storm drogue. There’s no explanation as to why. We disagree; weight placement should be used in most situations.

Your statement regarding rode specs for the parachute sea anchor is inaccurate. Specific rode diameters for parachute sea anchors have been used in California, since the late 1940s with an excellent track record of success.

Do you know the difference between 5/8” and 1” nylon rode if shock loading is involved? Only a few hours longer before the 1” rode breaks. And Dyneema? It usually increases shock loading if not properly weighted.

Your statement regarding “not all boats can ride to a sea anchor” is also inaccurate. The trick again is to remove the slack rode. Parachute sea anchor deployment tests from the U.S. Navy’s unmanned Sea Hunter confirm not only the importance of Rode Tension, but how it impacts sea anchor sizing. The Navy test reaffirms NASA’s original testing of a low-stretch sea anchor system for floating space capsules. Boat design can factor into whether or not a boat will ride better head to wind or in a hove-to position.

Snapping drogues we believe can be better controlled if you add the proper amount of weight and rode length. It all boils down to limiting slack rode as much as possible. The information mentioned in this post is published in more detail on the internet.

[Fi2010]

Originally Posted by thinwater

No, Landfall Navigation has another manufacture set up. No changes in construction.

Fiorentino is the last manufacturer that builds their own equipment, including the Shark. There's only some minor changes to Landfall's drogue.

[Fi2010]

Originally Posted by thinwater

Morgan's Cloud / AAC just reported on the probable cause of Goodall's drogue failure.


Sorry, no spoilers. It is behind his paywall.


https://www.morganscloud.com/

Looks like construction is going to be what Morgan's Cloud focuses on as the central issue. Seems to be the main theme of protecting the JSD. Ironically, if the JSD promoters would stick with Don Jordon's weight recommendation for the JSD, we'd likely see less failures of the JSD. It's all written in Jordon's report.

[Dockhead]

Originally Posted by Fi2010

Looks like construction is going to be what Morgan's Cloud focuses on as the central issue. Seems to be the main theme of protecting the JSD. Ironically, if the JSD promoters would stick with Don Jordon's weight recommendation for the JSD, we'd likely see less failures of the JSD. It's all written in Jordon's report.

Why so coy?


Different reports say that:


1. The drogue was undersized, and her boat was likely overweight
2. The failure occurred where the bridles attached to the drogue
3. The rope used was nylon

4. The bridle attachment was not by a splice, but by cow hitches to a Flemish loop, like this:





which significantly reduces strength of the rope, for both the bridle legs (the cow hitches with tight bends around the other rope) and the drogue end (the Flemish loop).





I have said it before: I would not use nylon for a drogue, ever, nor would I ever use knots. How many broken nylon ropes have I seen, from cyclical loads, including on my own boat. For a drogue, you don't need the stretch, and you sure as hell need resistance to chafe. This story makes me that much gladder, that I used UHMWPE single braid, spliced only, and the rope one size bigger than Jordan's spec, mostly 14mm, average breaking load 12 tonnes, to make my own drogue.

[Dockhead]

Originally Posted by Fi2010

. . .
Snapping drogues we believe can be better controlled if you add the proper amount of weight and rode length. It all boils down to limiting slack rode as much as possible. . . .

I think elasticity of the rode also has a lot to do with it.

[conachair]

Originally Posted by Fi2010

Ironically, if the JSD promoters would stick with Don Jordon's weight recommendation for the JSD, we'd likely see less failures of the JSD.

What failures are these? Suzie's does seem to be very likely small for the baot weight and had a knot fail (which had been already changed to a splice by the manufacturer) .
Are there documented failures not due to chafe?

[conachair]

Originally Posted by Dockhead

I think elasticity of the rode also has a lot to do with it.

How would that work?

AFAICS It's completely different to anchoring where the boat is moving and a snubber slows the boat down over a longer distance, with drogues there's a huge wall of water trying to move the boat, elasticity won't slow the wave down, if you want to slow the boat down then a few metres of stretch won't make any different to the force needed to keep the boat slowed down as the monster passes below you. May even make it worse by letting the boat speed up a little before the full force of the drogue takes hold.
Guessing a lot, but I would guess Don would have went for dyneema if it were available as a practical alternative back then.

[mikereed100]

We made a JSD using the Sailrite kit for the cones, attaching them to nylon rodes. The cones were 2oz ripstop and, after only a few hours deployed in F9 conditions, were shredded beyond use. The trailing edges were frayed nearly as much as the leading edges. The cones at the front of the drogue were affected more so than those at the rear. Sailrite no longer offers cone kits, which is probably a good thing. We made a new JSD, using 4oz polyester and hemming the leading edge. We re-used the nylon rode, as it is still in good condition. If I were to do it again, I would probably go with an even heavier weight cloth for the cones and would spring for UHMWPE rode. A 360' drogue with cones is a beast to move around the deck and store, and even heavier when wet. If starting from scratch, using UHMWPE is almost a no-brainer as the cost vs nylon, when matched for breaking strength, is roughly equivalent.

A quick comment on attaching the drogue to the boat. A friend recently deployed his JSD, attaching the bridle arms to welded stern cleats using the standard round turn and cleat hitch. The drogue ran out smoothly, but he then watched helplessly as the new nylon line slipped right off the cleats, one after the other, and his new drogue disappeared under the waves. A good reminder to use eye splices, or better yet, eyes shackled to chainplates that eliminate any chance of chafe.