Jordan Series Drogue in Dyneema

[oldbilbo]

How does one ensure the dog bone doesn’t fall out when there is no tension?

I think a couple of nylon cable/'zip' ties would do that, easily and cheaply.

[Breaking Waves]

Originally Posted by fxykty

A being better and the loops not connected to each other.
Alternative B, the loops are still girth hitched together and still are compressing each other, but have wider turns.

A would (I believe) have 100% strength (if the bone was > 1.2x rope diameter). But I personally would want to do some testing and experimentation to make sure an off-axis pull with not pull it apart. There is a lot of potential load and the boat can skew around. So, IDK, I have never tested that solution for off axis loads - might be feasible or might not.

B would (I believe) be stronger than your current solution, while (probably) not 100% after long term compression loading. Is probably more stable than A under off axis loads.

For dogbones . . there is a C solution . . . take one bridle eye left to right thru the rode eye and put a dog bone thru it and the other bridle right to left thru the rode eye and also a dogbone thru it - no off axis issues and no compression issues, but still a 1:1 bend where the eyes go thru. and also double the amount of metal.

The 'standard' way to do this is with rigging or spreader plates. In this specific case, take some aluminum plate in thickness about 1.5x line diameter (of the load-bearing line diameter not including the protective cover diameter). Cut it into a triangle. Drill 3 holes near each corner, 1/4 round (route or file) all (holes edges and outside of plate) the edges. The highest strength way is direct eye splice to each hole, but that does not allow disassembly (which may or may not matter). You can put spliced eyes thru each hole and a dogbone on the other side to keep them from pulling thru - this does not have the off-axis concern of the above A/B solutions. Those are all 100% strength solutions. Alternatively, you can cow hitch thru each hole, which loses a little strength but is simple. You can also use shackles with direct eye splices to the spreader plate, which allows it to be disassembled (and 100% with the shackles properly sized) but then you are starting to have quite a bit of metal.

I personally would not have any problem with your baseline solution (the all textile cowhitch) because you can pretty easily 'oversize' the bridles and the first section of rode to cover the small strength loss.

But if trying to do it 'correctly' I personally would use a spreader plate with direct eye splices. I'm not sure why you would need to disassemble but if you do, you can always just cut an eye off and only lose a meter (or so) of line.

[oldbilbo]

'A spreader plate...'


Perhaps like this one, from an arborist's supplier? This particular item is 'rated' at 65Kn/6.5tons which would be insufficient per se.







Perhaps there's better mileage in Australian writer Jonathan Reeves' idea of screw-together Low Friction Rings in stainless, mounted in a plate....




....and here





He's developed the idea for an anchoring bridle, for his own catamaran. Certainly, the idea could be scaled, and provide better D/d ratios for bent rope fibres.

[Breaking Waves]

Originally Posted by oldbilbo

'A spreader plate...'


Perhaps like this one, from an arborist's supplier? This particular item is 'rated' at 65Kn/6.5tons which would be insufficient per se.

ofc you need sufficient strength.

I would believe Ti would give you the best weight for the necessary strength. But Aluminum is rather easier to get and work. SS would be somewhere between.

I'm surprised at the (low) rated strength of that one you posted I'd love to see a test to failure to better understand that number. However, I do know I can deform the aluminum in low friction rings with my 20 ton hydraulics . . . so perhaps we do need steel or Ti here for the ultimate loads. This would not be a hard job for a machine shop in SS - no need for the screw-together rings, just machine a solid plate.

I always have a bit of cognitive dissonance about drogue loads . . . because 99.9% of the time they are not all that high, even in (real actual) offshore storms. The highest I ever measured was 1600kgs . . . . but I also know Jordan calculated worst-case breaking wave loads of (around) 60% of displacement. I guess I personally don't mind if the spreader plate distorts (and later needs to be replaced) but does not fail at that ultimate once-in-a-lifetime load - but I can understand how others might want to spec that well within the working load.

[Breaking Waves]

If you do want something like 20-ton actual working load (with a safety factor) you need some significant metal (weight) ..... https://www.lift-it.com/gn-triangle-...plate-type-tr1

but fxykty's 12mm dyneema probably has a breaking strength around 15000kgs (?) . . . . at a 5:1 safety factor that would be a 3000kg working load (using human safety factors) . . . . so actually not a terrible match with your arborist plate.

[Methersgate]

I think the case for using Dyneema or equivalent becomes overwhelming as the boat gets bigger. My boat is 25.4 tonnes at full load. I bought a 180 metre reel of 22mm Marlow Doublebraid (“about right” for strength) a couple of years ago. I’ve since cut it up into lengths for this, that, and the other, but I had great difficulty manhandling that reel. I honestly doubt if I could get a drogue made with this stuff over the side in good order in blowing weather, and getting it back is not to be thought of. Dyneema is the only practical choice.

[oldbilbo]

Originally Posted by Methersgate

I think the case for using Dyneema or equivalent becomes overwhelming as the boat gets bigger..... Dyneema is the only practical choice.

I won't disagree.... However, one must take ALL the lessons from Barry Deakin's research research into Yacht and Ship Stability at the Wolfson Unit/in the 80s on board....


....that 'a breaking wave 60% ( trough to crest ) of the beam-on boat's length WILL capsize All boat models tried.'


For Methersgate's Nicholson 55, that's a 36' wave. Yes, those do occur - and certainly did in some of the lethal storms that caused Don Jordan to hunt for a solution, but there are far, far more around of the size that would threaten a 30' Jester-sized boat..... And there are many hundreds of sailboats around that size.


It troubles me that manyowner/skippers of relatively modest-sized boats imprudently dismiss the possibility of encountering a breaking wave of 'their' size..... who DO occur all round the shores of Britain. Ireland and France - and, no doubt, around the USA as well.


Even a rudimentary glance at a simple 'Risk Analysis' matrix will highlight that a likely 'high frequency of risk event' requires a response. "It won't happen to me" doesn't cut the mustard....

[Methersgate]

I agree with @oldbilbo.

[Breaking Waves]

Originally Posted by oldbilbo

'high frequency of risk event'

I'm curious what you think the frequency or probability of encountering a 60% beam breaking wave is for a skipper watching the weather?

The actual empirical frequency of yachts being capsized by breaking waves is reasonably low, and most of the incidents are in 'particular circumstances (like crossing a shallow bar) which could have been/should have been avoided by a prudent skipper and in which a drogue would probably not have been much use (the incident with Low Speed Chase at the Farallones being an example - https://cdn.ussailing.org/wp-content...port-FINAL.pdf).

Excluding bar entries, it is usually (empirically) racers (and 'rallies') who get involved in these incidents (Fastnet, Sydney, NZ to tonga rally). They often leave with forecasts which are not really very prudent and often don't seek shelter or 'detour' when prudent and often don't deploy speed-limiting storm tactics. Prudent sailors with weather knowledge can most often (yes, ofc not always) avoid these dire situations - that knowledge has become much better and much more easily available to a sailor at sea over the years.

Note: I am a supporter of people carrying drogues. I believe they have value. But I also believe a prudent skipper's likily frequency of encounters with breaking waves is quite low. We blue water sailed for 15 years, averaging offshore 10,000miles/year, in high latitudes, and saw very very few breaking waves which could have capsized us.

It is really a quite safe sport. Bicycling, which is my 'other' passion, is at least an order of magnitude more dangerous.

[oldbilbo]

In a broad sense, BW, I'd agree with most of your comment.... but each 'over-simplification' properly needs a more detailed examination. And this thread is not really the place for such a divergence.

The statistics on waves of Hs and Hmax are easily searched online. The more research is done, the more frequently troubling anomalies are found..... which change the 'comfortable' theoretic modelling done. Here's an 'anomaly' pic taken on a summer's day just a few miles off the North Cornish Coast.





My boat wouldn't cope with that. Lifeboat cox'ns around there are also fishermen, and they tell me of such 'surprising' waves.


I agree certainly about prudence.... and acquired knowledge, of e.g. weather, boat handling, fatigue effects, etc. but I wouldn't agree that sailing is inherently safe. It only becomes 'acceptably safe' IMHO through the exercise of the above, and the exercise of judgement sufficient for the task.

Others are free to be otherwise, to be 'risk-takers', but I see my role as 'risk mitigation'.... through knowhow. I survived a couple of decades of rock-climbing, then a couple of decades of operational military flying and half a century of sailing, due to identification of risks and effective management of them.


I identify there's some likelihood of me wanting to deploy a JSD at some point, so I want to hoist in all the knowhow others have learned the hard way. That 'prepping' done, I can better focus on the sailing, lookout, weather prognoses, and landfall planning.

[Breaking Waves]

Originally Posted by oldbilbo

In a broad sense, BW, I'd agree with most of your comment....
. . . . .
I identify there's some likelihood of me wanting to deploy a JSD at some point, so I want to hoist in all the know how others have learned the hard way. That 'prepping' done, I can better focus on the sailing, lookout, weather prognoses, and landfall planning.

Sure, agreed . . . . all that is perfectly sensible.

And as I said I am an active user and proponent of drogue use. However, my personal experience has been that the most frequent usage (by far) are NOT in the true 'huge breaking wave survival' situation . . . but to slow and stabilize the boat in extended storm-force situation (with waves with breaking crests but not 'breaking waves'), where you can get fatigued and the vane or autopilot might have trouble steering. This is 'prudent' usage rather than 'survival' usage . . . it reduces fatigue and possible equipment breakage. . . . which reduces the possibility of a 'cascade of events' causing an actual serious problem.

My point above . . . . was this (in my experience) much more frequent usage case has significantly different (order of magnitude lower) load requirements than the 'survival worst case once in a life time' situations. And if you design working load to this case you end up with a rather easier to handle device, which in a 'virtuous circle' means you will in fact probably use it more often.

We in fact had two drogue system - the frequently used one, and the survival one. The frequently used one I used a lot and fine-tuned and I think it was 'best practice'. The survival one we tested but I honestly was never totally confident it was 'best possible design' and experimented with variations which I believed were improvements . . . . but there was never really any way to accurately simulate/test actual survival breaking wave usage (the dynamics inside a true huge breaking wave are pretty extraordinary) - so it was a bit of a frustrating development process.

"The statistics on waves of Hs and Hmax are easily searched online. The more research is done, the more frequently troubling anomalies are found..... which change the 'comfortable' theoretic modelling done. Here's an 'anomaly' pic taken on a summer's day just a few miles off the North Cornish Coast."

Yea I've seen all that data . . . . which changes what science thinks the right output from models should be . . . . but does not change my personal assessment of probabilities (which was never based on numeric models). Large waves per say are not a problem. Wave shape is the problem and (I believe) that is not able to be quantified by satellite yet. One-off huge waves with bad shape are ofc very dangerous . . . but problematic for drogue usage - becaue they are one-off you might well not realize you need the drogue, and it is not clear to me that any of the drogue system will actually keep you from being overwhelmed if you encounter that 100' terrible shaped wave - take a look sometime at the length of white water in a large breaking wave and compare it to drogue length (hint most drogues will be all or mostly in the foam) - I guess it will kill a small yacht no matter. And that picture . . . . surely there is a 'special circumstance there - a counter-current or shallow bank or ship wave? And surely the forecast that day was such that a prudent skipper would have been in the pub?

[Breaking Waves]

so yea that photo - waves after Hurricane Epsilon in a coastal area with both shallowing waters and current. And apparently, they were responding to people who had been swept off a headland rather than off a boat. The local skippers were in fact all at the Pub

[Dockhead]

Originally Posted by Breaking Waves

If you do want something like 20-ton actual working load (with a safety factor) you need some significant metal (weight) ..... https://www.lift-it.com/gn-triangle-...plate-type-tr1

but fxykty's 12mm dyneema probably has a breaking strength around 15000kgs (?) . . . . at a 5:1 safety factor that would be a 3000kg working load (using human safety factors) . . . . so actually not a terrible match with your arborist plate.

The smallest of those lifting plates weighs 10kg


How about one of these?


https://www.lgrigging.com/products/grade-80-pear-link/





The 3/4" one weighs under a kilo, breaking load 28 tonnes.

[Breaking Waves]

Originally Posted by Dockhead

How about one of these?.

If I were fxykty, I would just keep what he has (perhaps uprate the bridle and leader if he has any concerns) - it is nice and simple and light.

But yea there are various links that could be used. Somewhere you could find some Ti ones that would be lighter than the steel (I know they exist because seen them on exotic parachutes). The plate approach 'should be' more deformation-resistant (than rings), and are the commercial 'go-to' when you want to be absolutely sure . . . and if you wanted to be weight concerned you could easily do machining to remove quite a bit of unnecessary weight (easy job for an engineer with a FEM package) - I have again seen that done. I think these were all custom jobs but with FEM and cad/cam is not all that difficult.

I actually like the basic design of the arbor plate that bilbo posted. If you put the rode loop around the outside and and the bridle loops tru two holes . . .even if it deforms a bit the join is still all captured and safe. You only need two holes for our application, and you could machine out some weight. I guess for our application it would be rather stronger than what they seem to be quoting there, as they seem to be using it as a friction device with rope moving thru the holes (which creates heat and wear and off load vector) - where as our application is a pretty nice static load vector with no movement.

The toggle options would be awesome in applications where the load was always on-axis . . but I just don't know how well they will do when the drogue is moving side to side . Might be good, but might not be, would need some testing to deterimne.

There are actually a ton of options and I think for a drogue you can over think this. The only ones I have seen break at this join used knots to create the join which is yea a bad idea.

I guess I am a bit to blame here by saying that fxykty's solution did create a strength loss and was not 'best practice' . . . but I will fully admit when I said that I had just completed a project where weight was in fact a major concern but we had access to custom engineered and machined Ti parts so I was not thinking much about off the shelf steel weight issues.

[oldbilbo]

where as our application is a pretty nice static load vector with no movement.

.....and well-cooled!


I'm certain Jon Neeves could readily come up with a late-prototype using his screw-in LFRs and some locking fluid. He's more than halfway there already with his existing bridle-plate designs....