Composites expert

[zoidberg]

Wing Mark, with courtesy, your emphatic assertions would seem to be based on a number of assumptions, which can and have been shown to be false. Conclusions such as yours are also shown to be false.

There is a principle in the construction and the 'use in anger' of the JSD that proponents of elastic energy-storing materials such as nylon rope quite fail - or refuse - to see. The JSD itself absorbs the energy imparted by a breaking sea-crest, progressively, by means of the deep inverted catenary the rode adopts in the water column. That's a function of the considerable weight on the end....

Don Jordan himself indicated that the 'stretch' and the recoil of nylon rope was undesirable. He used nylon rope in his proof of principle tests with the US Coastguard because that's what he had available, and he didn't have a budget for or access to anything better in 1980. Nylon rope is known to lose a substantial proportion of its dry strength when saturated. It also weakens much more, and more swiftly, during cyclic loading/unloading than all other commonly-available synthetic fibre ropes.

Long-distance sailors have been using JSDs for 40 years, worldwide. There is a significant body of published experience about how the devices work, and also how that user-knowledge and today's materials science can improve markedly on the early examples. It warrants study - and that's exactly what this correspondent had been doing for more than 3 years now. Studying it.....

The 'ripping off of a fairly substantial cleat' is exactly what I'm seeking to avoid, by in-depth understanding and wholly adequate reinforcement - not guesswork. I have checked my thinking with a number of reliable experts in rope technology, and I am wholly satisfied that the rodes I have acquired will be more than sufficient to the task. It is, after all, my soft little pink ass that I'm putting at risk, and I've been quite successful in keeping that from harm for rather more than 50 years.

I agree with you entirely that the stainless strap shown above with its 13 hex-head bolts is seriously ugly. An eyesore.....

 

[William_H]

OK to mount the pad eye as pictured you really want reinforcing of GRP that will ensure the GRP is not the first part to let go. Basically you fit a backing plate to spread the load out such that if the section of GRP were to be pulled out it will have a large perimeter to break. So if you started with a metal backing plate the size of the pad eye it could pull out a square of hull that size. If you increase the area of the metal backing plate you increase the area and circumference of the section of GRP to be pulled out. As said front first.
So much depends on the strength of the existing hull thickness. Assuming you have access to the inside of the hull I would suggest a big patch of additional GRP somewhat disproportionally foward of the pad eye. Even to the extent of extending well forward into the hull. Then use a backing plate to spread the very high pressure of the nuts.
How thick the GRP extra backing? Much depends on what satisfies you. The thickness of the hull at that point ie I would guess about 5 mm would be a good start for the thickness of the added pad. Depending on what cloth or mat you use will determine end thickness. There should be data available there. Perhaps it does not matter so much. You just keep adding layers.
Now I would suggest you consider carbon fibre cloth. More expensive but nice to use with epoxy and vastly stronger (stiffer) than glass. Do taper the pad so thinner at the outside and thicker nearer the pad eye. Not sure about end on (side ways) load but for pulling outward this gives a varying profile of thickness to give a gentle bend rather than sharp edge to bend against. If you go for a narrow very long forward backing (like a chain plate goes down) you might also consider embedding kevlar layers to strengthen the backing.
Sorry plenty of ideas on how to make it strong just no idea on how much is enough. ol'willtape

 

[Wing Mark]

Exactly how many yachts have been saved by towing drogues on dyneema?
This looks like elaborate plans for one particular disaster scenario.
Is the JSD the current 'must have' disaster prep?
When I worked on other people's boats 30 years ago, wasn't it big parachute sea anchors?
Which worked really well in the one scenario they were any good for, Just luggage when any of the 1000 more likely problems happen in reality.

 

[geem]

Exactly how many yachts have been saved by towing drogues on dyneema?
This looks like elaborate plans for one particular disaster scenario.
Is the JSD the current 'must have' disaster prep?
When I worked on other people's boats 30 years ago, wasn't it big parachute sea anchors?
Which worked really well in the one scenario they were any good for, Just luggage when any of the 1000 more likely problems happen in reality.

The problem its designed for is storm survival. What would your solution be?

 

[zoidberg]

Aye, right.

Aircraft wings are today largely 'bonded'. Composite panels are designed and built into probably all new aircraft this century. Would you have us return to rivets, to wire and doped canvas?

I carry a liferaft, lifejackets, and fire extinguishers. Those are selected to address just a few of the '1000 more likely problems'. It's my responsibility to identify and provide kit for those situations I deem likely, and/or where the outcomes are severe enough to warrant 'precise prior planning ( to ) prevent piss poor performance', to borrow a well-known military phrase. My JSD is but another of these 'preparations'. There's little point in doing half-a-job.

 

[Wing Mark]

The problem its designed for is storm survival. What would your solution be?

Lots of yachts have survived storms by not using dyneema-rode drogues.
How many have survived what storms using a dyneema rode drogue?

My strategy for storm survival is to avoid storms.
I don't think any of the yachting I'm likely to do is likely to be made safer by carrying a large complicated drogue. Particularly a dyneema one.
Be sure to let the lifeboat know you're trailing a load of dyneema, it's not great with propellors.

 

[Stemar]

I'm not going to criticise your decision; I think it depends on the kind of sailing you're planning. Going across oceans? Yes, I'd want a JSD. The odd trip across the Channel or the Irish Sea when I've got reliable forecasting? Not so much, I'd use the space for a couple of cans of diesel instead

 

[thinwater]

I'm looking for professional expertise in composites. Someone to tell me how many layers of what bi/tri/quadraxial glasscloth to bond in, for a specific reinforcement task.
Any pointers?

An engineer would assume that was a joke.

You are asking for expert advice, on an open ended question, on a forum. These are not simple calculations with a lot of variables. Expect to spend many hours with google and some more hours with textbooks.

There are MANY designs for JSD anchors that could work. Jordan;s original design was never optimized--it was a simple, generalized solution for the masses. He was a big believer in keeping things simple. But I don't think one has failed. You could even do it without metal. Just spread the load. But you have to do the math.

The straight, horizontal design assumes a pull in one dirrection, but that is NOT what drogues do in a storm. In a knock-down, the load will be dirrected downwards and the strain falls almost entirely on just 1-2 bolts. It works because it is suffiuciently conservative and something else will break first. It's an intriguing puzzle, because although it looks like a chain plate, it is NOT a chain plate (only one direction of pull).

 

[zoidberg]

But I don't think one has failed.

Thanks, Drew, but one did.

In the Southern Ocean.... to Suzie Goodall.

It was very widely reported..... and discussed worldwide..... and some of the 'questionable assumptions' that had been made repeatedly over several decades were re-examined here and there. Some of those 'folk myths' are still being peddled, even in this thread.

It works because it is sufficiently conservative

That's the approach I'm taking, as the numbers quoted in earlier posts should attest. Interestingly, I happen to have a pair of substantial polished s/s plates of approximately the shape in the above diagram. Even if I use them, the question of provision of sufficient reinforcement still arises. So also does the question of type, size, number and spacing of bolts. That in itself is a complex question which demanded quite deep reading ( another set of internet 'rabbitholes' - see #8 ), but I'm fortunate to have near at hand the UK Technical Rep for BUMAX Bolts, who has been kind enough to root out and provide 'batch testing' results for the bolts I acquired.

He advises that any two will do the described task with more than sufficient redundancy. The outstanding question is not whether I will ever need a JSD, nor what modern fibre/construction/diameter the rode should be, nor even how best to join the rode to the bridle. The outstanding question is how optimally should I provide the desired reinforcement.

We know well enough that the assumptions and calculations made for the design of big-budget 'Hugo Boss' were found wanting. We know well enough that the assumptions and calculations made for the design of big-budget 'Team Philips' were found wanting. There are other examples.

I'm gnawing and fretting at this question until I can say to myself that I explored every avenue available to me, and that the answer I found and implemented was 'sufficiently conservative'.

 

[geem]

Lots of yachts have survived storms by not using dyneema-rode drogues.
How many have survived what storms using a dyneema rode drogue?

My strategy for storm survival is to avoid storms.
I don't think any of the yachting I'm likely to do is likely to be made safer by carrying a large complicated drogue. Particularly a dyneema one.
Be sure to let the lifeboat know you're trailing a load of dyneema, it's not great with propellors.

I don't know of any sailor who plans to sail through life threatening storms. We generally plan to sail oceans at the correct time of year to avoid the worst weather. The problem is weather doesn't always do what it's supposed to do. Occasionally you get caught out.
You strategy to avoid storms works well when sat in your armchair. It less effective when in the middle of an ocean.
I don't think you have an understanding of how a JSD works. The stretch in the rode is irrelevant to the performance of the drogue. The drag effect is created by the mini parachutes. (165 of them on mine). The multiple mini parachutes always ensure the boat is recieving some drag effect thereby giving a constant pull. Unlike a large parachute deployed from the bow to stop you a JSD is deployed from the stern to slow you down and keep the stern to the seas.
If I was to use mine mid Atlantic, I don't think we would have much concern about the RNLI.
If you are a coastal sailor then a JSD is not for you

 

[fredrussell]

Someone earlier mentioned attaching the JSD to something that attaches to (or is a continuation of) the hull deck join. Would this not work? It’s a very strong part of boat I’d say.

 

[geem]

Someone earlier mentioned attaching the JSD to something that attaches to (or is a continuation of) the hull deck join. Would this not work? It’s a very strong part of boat I’d say.

Mine fixes to the aluminium toerail. s/s plates bolt through the holes in the toerail. There is then a huge shackle that fixes to the plates. The toerail is substantial and bolted through the deck with M8 bolts every 100mm.

 

[thinwater]

Thanks, Drew, but one did....

Incorrect, Zoidberg. The bridle failed, not the chain plates (or please post a link explaining this chain plate failure or ANY drogue chain plate failure--I could be wrong, but you will have to show us).

Goodall Drogue Failure
Goodall drogue failure II

 

[zoidberg]

Nowhere did I specify a chainplate failure, Drew. I pointed attention to your own vague and unspecific statement in #28 "But I don't think one has failed. "
One has. You've made a wrong assumption and gone charging off in the wrong direction.

I myself queried Susie, at her presentation during a Southampton Intl Boat Show a couple of years back - mounted by her co-sponsors Marlow Ropes - in the presence of their Paul Dyer and David Mossman, and she told me directly she could not be more specific about EXACTLY what part failed, for she'd been unable to examine the residual bits. Do remember it was night, a severe storm was raging, the boat had been knocked down and dismasted, and she was injured. She considers that the most likely point of failure, and everyone - including me - agrees it was probably the rode/bridle knotted attachment.

You show some pics of example 'flemish loops'. There are other pics in existence - I posted a couple on here in the immediate aftermath, and contributed them to the early discussions within AAC and another forum - showing Susie's actual JSD laid out on a pontoon and being rolled into its deployment bag by Susie herself..... with the double-figure-of-eight knots ( 'flemish loop'? ) clearly visible.

There were questions raised at the time, and in forums since, that not only was the 'flemish loop' arrangement with 'cow hitches' a wholly inadequate means, but also the specification of the rope-rode itself was likely inadequate for the LADEN weight of Susie's boat. I know from asking far and wide that more than a few owners and specifiers looked at Don Jordan's simple tables and entered them using the boat-builders' catalogue LIGHT SHIP or unladen weight. There is one huge difference, as John Harries' article explains....!

I point no fingers at Susie, nor at Angus Coleman, but I'm in full agreement with the article collated and published by John Harries in 'AAC'....

Mistakes were made in choosing which Ocean Brake series drogue was right for Susie’s boat and in using the figure eight knot in place of a splice.

It is valuable to read/digest that article in full, and also to recognise there are still people around advocating the use of 'flemish loops with cow/cinch hitches' for this application.

It has been my task, in building my own JSD, to challenge every assumption and seek satisfactory answers. I won't blindly and lazily accept the loud unsupported assertions of a few "because that's what others do" and "that looks good enough".

 

[thinwater]

Nowhere did I specify a chainplate failure, Drew. I pointed attention to your own vague and unspecific statement in #28 "But I don't think one has failed. "
One has. You've made a wrong assumption and gone charging off in the wrong direction....

Just chill. This is a chainplate reinforcement thread and you know that. Any response would be a pitch in the dirt. Just decide what you are going to do, or pay an engineer who has invested the time in learning the craft.

 

[Wing Mark]

....
I don't think you have an understanding of how a JSD works. The stretch in the rode is irrelevant to the performance of the drogue. The drag effect is created by the mini parachutes. (165 of them on mine). The multiple mini parachutes always ensure the boat is recieving some drag effect thereby giving a constant pull. Unlike a large parachute deployed from the bow to stop you a JSD is deployed from the stern to slow you .....

Presumably, if low stretch and high strength/weight was desirable, Mr Jordan would have specified polyester or some other rope with those characteristics in the first place?
I suspect he specified nylon for the exact same reasons it's so common in anchor rodes..

If the wave conditions are such that your tow line can go slack and then go tight, it will be subject to a serious jerking force.
Whatever you are towing, whether it's a drogue, a tender or another boat.

You can get waves which allow a tow to go slack and then suddenly tight without leaving Poole Harbour.
To say that no wave conditions which do this could possibly occur in an ocean storm seems like a pretty bold leap of faith.

Please give details of yachts which have weathered storms using a dyneema rode JSD.
BTW, the failure of the rode on Ms Goodall's JSD only suggests the forces can exceed whatever figure you concoct for its breaking strain.
It does notihing to even suggest the forces are limited to any other figure.

It does perhaps raise the question whether relying on a drogue and having it fail is a worse situation than not putting your trust in a drogue in the first place...
Letting the boat go when the forces on it are at a peak might not be the right idea.

 

[thinwater]

Presumably, if low stretch and high strength/weight was desirable, Mr Jordan would have specified polyester or some other rope with those characteristics in the first place?...

In fact, you need to read his comments more closely and some of his later work. He suggested lower stretch. Other than parachute sea anchors, all drogues are better deployed with polyester rodes (vs. nylon). The "give" comes from the cones ripping through the water, not the rode. Although the tail weight creates a catenary-like shape, the function is completely different from anchoring with chain (test one without a tail weight and you will see the real reason).

From the USCG report:
"Actually the model tests show that a highly elastic line is very undesirable because the boat may be capsized before the load builds up...."

"The series drogue,since some of the cones are near the boat where towline stretch is low, will build up load faster than a conventional cone or
chute at the end of the towline. A computer study shows that two seconds after wave strike, the series drogue will develop 40%
more load than an equivalent cone or chute...."

Later, Don commented that Polyester and Dyneema would have advantage, but I cannot find the link. It is well known.

Remember, that Don was retired when he wrote the report, and that the design and report was based ONLY on lab testing. He did not have the TIME or FUNDING to perfect the design. For example, the cone design has proven marginal and has been improved. He only looked at one design. He only looked at one rode, because of funding limitations. A great insite, but he did not consider the work finished.

 

[pandos]

Presumably, if low stretch and high strength/weight was desirable, Mr Jordan would have specified polyester or some other rope with those characteristics in the first place?
I suspect he specified nylon for the exact same reasons it's so common in anchor rodes..

If the wave conditions are such that your tow line can go slack and then go tight, it will be subject to a serious jerking force.
Whatever you are towing, whether it's a drogue, a tender or another boat.

You can get waves which allow a tow to go slack and then suddenly tight without leaving Poole Harbour.
To say that no wave conditions which do this could possibly occur in an ocean storm seems like a pretty bold leap of faith.

Please give details of yachts which have weathered storms using a dyneema rode JSD.
BTW, the failure of the rode on Ms Goodall's JSD only suggests the forces can exceed whatever figure you concoct for its breaking strain.
It does notihing to even suggest the forces are limited to any other figure.

It does perhaps raise the question whether relying on a drogue and having it fail is a worse situation than not putting your trust in a drogue in the first place...
Letting the boat go when the forces on it are at a peak might not be the right idea.

(Thinwater already said this...I was googling for the link?)
Jordan later commented that low stretch was optimal and for the reasons Zoidberg referred to earlier, although I understand that is the fact that the drogue is captured in the wave train far behind the one that is carrying the boat rather than cantennay in the water column which is the means of securing the boat and therefore any stretch as the boat surged down a wave is to be avoided.

Have a look here and the link in my post for loads of info.

3 strand polyester for a Jordan Series Drogue?

 

[thinwater]

3-strand line is generally a bad choice for any variable load that is not secureed against rotation at both ends. It will rotate under occsilating load and can hockle.

 

[pandos]

3-strand line is generally a bad choice for any variable load that is not secureed against rotation at both ends. It will rotate under occsilating load and can hockle.

That point is fairly well made in the thread I linked to..