Jordan Series Drogue experience

[Mycroft]

I went with an ACE Dyneema series drogue. The Dyneema increased the cost, but it greatly decreased both the bulk and weight of the thing. To help with deployment, I bought a deployment bag from Ocean Brake. My 38,000lb boat's canoe stern was a challenge. I had Port Townsend riggers fabricate chainplates with a welded perpindicular eye. They each use 8 x 3/8" bolts with heavy duty backing plates.

[NevisDog]

Originally Posted by NevisDog

...
- Sailrite US: 2.6 oz nylon cones, no reinforcing = $313 / 100 cone kit.
- Ace Sailmakers US: 6.5 oz dacron, stitched over hem = $700 / 100 cones.
- Ocean Brake UK: 4.2 oz nylon, taped edges = $834 / 100 cones, including rope!
- 'englishseadog' UK: 7.2 oz dacron, taped edges = $442 /100 cones.

Not sure yet but 'englishseadog' may be the eBay title for Neptune's Locker (at least both are in Weymouth, UK). All prices in USD.

It turns out that Ocean Brake, Neptune's Locker and 'englishseadog' are all one and the same company. They use only 7.2 oz dacron with fully taped edges; they haven't used 4.2 oz for past 'four or five years' (and they will now update their website!).

[NevisDog]

Originally Posted by NevisDog

... Fig 24C [in the drogue coastguard report] then shows a 300% increase in towline stiffness results in only a 20% increase in (maximum) drogue load (again based on a single drogue).

I would hate for the above statement to be misleading, so I investigated the comparative stretch ('stiffness') of nylon -v- Dyneema.
Pelican Rope.com gives some useful information, which I hope I am interpreting correctly:
Dyneema (SK75) has an elongation at break of 3.5% (wet or dry - it doessn't absorb water), while wet nylon breaks at 20-30% elongation.
Taking worst case, this represents a near 900% increase in 'towline stiffness', but of course the increased dynamic loads due to this increased stiffness will necessitate an even stronger rope, making the situation even worse.

Extrapolating the coastguard report results for this new material (new in as much as the report never envisaged), the apparently linear relationship between 'stiffness' (I interpret this as 'stretchiness') gives a 60% increase in maximum load if Dyneema is substituted at the same strength, but we should then use 60% stronger Dyneema. Will this increase 'stiffness' a further 600%, hence a further 40% increase in maximum load, requiring yet stronger Dyneema? Eventually leading to the point where it will simply rip the eyeplates from the hull?

After all, we are substituting something with far less stretch than steel cable. Has this been properly thought through by anyone?

[DumnMad]

3 strand nylon specs - 20% stretch at 50% breaking load.
300ft drogue at say 50% load at the ship attachment, 0% at the end = 30ft stretch at 25% average loading.
Boat can pick up a bit of speed in the 30ft surge it would take for the drogue to take up the full 50% load. Hence the extra wear on cones closest to the ship.
I have a greatly oversized poly rope drogue so little stretch, but if I was to have a Jordan drogue it would be Dyneema.

[DumnMad]

Don't forget that even under bare poles you will already be dragging the drogue through the water and there should be no slack in the rope.
When the wave hits you are pushed forward and the drogue load only increases in proportion to the boat speed, not in proportion to the wave load.
The boat's inertia comes into effect and the speed will increase slowly as the force of the wave applies the acceleration. Just like a heavy truck cannot pick up speed the same as an high powered car.
Since drogue drag resistance is proportional to its speed through the water, a featherweight race boat with much less inertia could have more attachment load than a 20t cruiser.

[CarinaPDX]

Originally Posted by DumnMad

3 strand nylon specs - 20% stretch at 50% breaking load.

For clarity, 3 strand should never be used for series drogues. The loads would cause twisting which could affect the drogues. The original design was for double-braided nylon. I had contacted Jordan and asked if 8-plait nylon could be substituted because the double-braid was not available in Europe at that time. I am forgetting exactly what he said, other than that it would have more stretch. I may have quoted that letter earlier in this thread; if not, I may try to find the letter.

Greg

[wsmurdoch]

While some might, with two degrees in engineering and 31 years professional experience, I would be loath to make a significant change to a dynamic mechanical design based on common sense reasoning or on long extrapolation of the data used in the original design. These things are frightfully complex. Before making any significant changes, I would wait for the completion of full size testing, small scale model testing, or extensive numerical computer modeling.

I built my Jordan series drogue following the published instructions only by adding hems to the front of the cones because it was easy to do and by relying on my boat's stern cleats because Pacific Seacraft assured me they met the stated strength requirement.

This is a place where Ace Sailmakers could step up and do the required work to update and improve the original design.

[NevisDog]

Originally Posted by wsmurdoch

...This is a place where Ace Sailmakers could step up and do the required work to update and improve the original design.

Especially since someone states above that they just purchased an "Ace Dyneema series drogue", one might expect Ace to have first determined the extra strength required in the rode and the extra load placed on attachment points. Jordan was quite clear - a rope with 300% less stretch creates a 20% increase in peak loading, and Dyneema is way, way beyond those parameters.

[estarzinger]

Originally Posted by wsmurdoch

relying on my boat's stern cleats because Pacific Seacraft assured me they met the stated strength requirement.

Really, your stern cleats (as installed) are rated to 9000 lbs (plus some safety factor)? How many/what size bolts used, and what are the backing plate dimensions?

Originally Posted by wsmurdoch

This is a place where Ace Sailmakers could step up and do the required work to update and improve the original design.

It is an enormously complicated piece of engineering to model the worse case breaking wave scenario. And Ace are a pretty small sail maker without that sort of skill or resource. Some good engineering university might be able to do this project, but turbulent water is quite difficult to model even with america's cup level (eg $m) resources.

Originally Posted by NevisDog

Especially since someone states above that they just purchased an "Ace Dyneema series drogue", one might expect Ace to have first determined the extra strength required in the rode and the extra load placed on attachment points. Jordan was quite clear - a rope with 300% less stretch creates a 20% increase in peak loading, and Dyneema is way, way beyond those parameters.

^^ basically no-one, including Jordan, knows what the loads are on these systems in the worst case type huge breaking seas. Jordan did do some calculations/estimates, but they are more of the 'back of the envelope' sort than real 'engineering'.

The loads on the system in 'bad storm' conditions is known. I and others have actually measured it. And the loads are relatively low and the typical dyneema rode will create no problem at all.

Thinwater here did some tests which suggested that the series system was not that sensitive to rode stretch or shock loads because the cones took up the extra load progressively.

I and several others users of dyneema rode series drogues use non-dyneema bridles. I did this primarily because dyneema was more slippery that I liked for winch/cleat attachment, but this also introduces significant shock absorption into the system if it is in fact useful.

As an actual user of such systems, I personally don't think the typical dyneema rode is going to create a problem.

[NevisDog]

Originally Posted by estarzinger

...Thinwater here did some tests which suggested that the series system was not that sensitive to rode stretch or shock loads because the cones took up the extra load progressively. ...

Thanks Estar, I forgot that all Jordan's/coastguard's stretchy/non-stretchy calcs in that report were done on single drogues, not series. I'm in process of buying the cones right now so thanks again for that reassurance; Dyneema certainly has some compelling advantages:
- zero water absorption (less weight on retrieval)
- lighter and less bulky
- fibre has 'low friction properties, which protect it from internal abrasion, (less heating?) resulting in long service lives in rope tensile and bending fatigue testing' - per PelicanRope website.

[thinwater]

Several thoughts.

1. Nearly all of the shock absorption cones from pulling the cones through the water and straightening the curve. There is also energy required to accelerate the water contained in the cones--this is often forgotten, even though it is the major factor with parachute drogue wave impact. Think of how heavy the ball of water contained in 24-foot chute is!
2. The nylon does not stretch as much as some have guessed, because the load varies along the length of the drogue. Yes, there is taper.

But the most important consideration, which will require some head scratching, is whether you WANT rode stretch. Jordan struggled with this, and in the end, relied on gut and empiricism. If stretch allows the boat to begin surfing, that is a bad thing, since the drogue now has to arrest the momentum too. Imagine trying to stabilize yourself in the surf by holding on to a rubber band, and then imagine a rigid railing. Neither will work. We need something in the middle, but we don't know if that is a nylon JSD, polyester JSD, or a Dyneema JSD. We don't even know the perfect number of cones, only experience and thumbnail estimates. We simply do not know, and I don't think statements of absolutes help the conversation. As Starzinger pointed out, this is really complex and the best answer, logically, may differ depending on the wave conditions in the specific storm and the characteristics of the boat.

And that is why these threads are interesting. Fun stuff, so long as we keep our minds open. Real experience comes very slowly, since folks like me will test in a light gale and at small scale, but not in scary weather.

Keep it up!

[thinwater]

I should add what I consider the most important lessons gained from testing:

• ALL singe drogues are unstable above 5 knots. The drogue pulls to the surface and will pull out of wave faces.
• A nylon rode increases the distance the drogue will recoil forward if it comes out. This is the BEST reason to use a non-stretch rode for single drogues.
• Low-medium force drogues do not experience impact forces in the sense that ground anchors or sea anchors do. They give, even the JSD. In order to create high loads, anything over 1000 pounds, I generally had to motor down wind and set a head sail. Really high loads required creating slack and getting a running start. Even then, 1500 pounds was a lot. For comparison, 1500 pounds is my working genoa sheet tension. Nothing special. That said, I accept Don's math for a possible worst case.

[DumnMad]

Originally Posted by thinwater

Several thoughts.

2. The nylon does not stretch as much as some have guessed, because the load varies along the length of the drogue. Yes, there is taper.

Keep it up!

30ft stretch in a 300ft nylon based drogue is calculated.

Only about 10% MBL which the averaged stretch from 20% at the boat to zero at the far end.
20% is the approximate stretch expected going from say 5% loading to the design load of 50% breaking load using the recognised FOS of 2.

[wsmurdoch]

Originally Posted by estarzinger

Really, your stern cleats (as installed) are rated to 9000 lbs (plus some safety factor)? How many/what size bolts used, and what are the backing plate dimensions?

The two stern cleats are 10 inch with four bolts each. The metal backing plates are larger than the spread of the feet of the cleat. The displacement of a PSC 34 is 13,500lb. The design load for that displacement per Figure 26 of the 5/87 CG report is 11,200lb. Per p.59 the required fitting strength is 70% of that or 7,840lb or 2,000lb/bolt. Now, not knowing the alloy, not knowing how to handle the off axis loading, and not knowing the strength of the FRP layup or the ajoining structure, I called the maker. They said it would be okay.

Originally Posted by estarzinger

It is an enormously complicated piece of engineering to model the worse case breaking wave scenario. And Ace are a pretty small sail maker without that sort of skill or resource.

I was invisioning doing something like Jordan did in his testing. Make up two drogues one with nylon rope and one UHMWPE, take them to the Columbia bar, and try them behind a USCG vessel in the surf with a 10,000lb load cell. (5/87 p.43) I'd bet the UHMWPE drogue would work fine and maybe be better, I just don't know it. It would be nice to have some data. I suggested Ace because they position themselves as the keeper of the Jordan Series Drogue.

Originally Posted by estarzinger

Jordan did do some calculations/estimates, but they are more of the 'back of the envelope' sort than real 'engineering'.

Years of work, two published USCG reports - 12/84 & 5/87, model testing in tanks and open water, computer simulations, full size testing of a towed 90 cone drogue, and full size instrumented testing on the Columbia River bar. Back of the envelope??? Not real engineering???

[estarzinger]

Originally Posted by wsmurdoch

Years of work, two published USCG reports - 12/84 & 5/87, model testing in tanks and open water, computer simulations, full size testing of a towed 90 cone drogue, and full size instrumented testing on the Columbia River bar. Back of the envelope??? Not real engineering???

Valuable work certainly. But also, yes, more 'back of envelope' than real engineering of the huge breaking wave scenario.

The two stern cleats are 10 inch with four bolts each. The metal backing plates are larger than the spread of the feet of the cleat. The displacement of a PSC 34 is 13,500lb. The design load for that displacement per Figure 26 of the 5/87 CG report is 11,200lb. Per p.59 the required fitting strength is 70% of that or 7,840lb or 2,000lb/bolt. Now, not knowing the alloy, not knowing how to handle the off axis loading, and not knowing the strength of the FRP layup or the ajoining structure, I called the maker. They said it would be okay.

Your boat will yaw in a storm with significant waves, so at some points all the load could be on one leg of the bridle/one cleat (I have seen that in actual practice, that is not 'desk theorizing') - so it is more prudent to size for entire expected load on one cleat/chain plate rather than to split the load.

There are a couple places where there are design loads stated, and they are not exactly consistent - but just fyi DESIGN LOADS and ATTACHMENTS it suggests 9000lbs (plus a safety factor) for your displacement. It does not really matter, because as thinwater and I have said, no-one really knows except the rough ballpark - 11k lbs would perhaps be an ok ballpark but with a pretty modest safety factor for the 'worst case'.

As to cleats . . . fyi - cleat test is useful reading - somewhat smaller cleats than yours. The strongest one, with 4 x 1/4" bolts went to 7000lbs. The advice for a 10-13k lbs loading is six 3/8 bolts (with a satisfactory deck layup). I believe Thinwater also did some cleat testing for PS but I dont have a link or copy handy.

I was invisioning doing something like Jordan did in his testing. Make up two drogues one with nylon rope and one UHMWPE, take them to the Columbia bar, and try them behind a USCG vessel in the surf with a 10,000lb load cell. (5/87 p.43) I'd bet the UHMWPE drogue would work fine and maybe be better, I just don't know it. It would be nice to have some data. I suggested Ace because they position themselves as the keeper of the Jordan Series Drogue.

The series cones will almost certainly take up progressively in that situation and spread/absorb shock loading. But in several regards that does not very closely simulate a storm with repeated 50' high x several 100' long breaking wave with undetermined depth of foam. Just for example . . . . The big wave may engage the entire series at once (because of the size of the moving water) which the bar waves will not, or there may be quite a bit of slack from snap back from prior big wave, or the foam may reduce the drag effect of the cones . . . .we just don't really know. I don't know if you have been in a severe storm with large ocean fetch? But the dynamics are pretty different than bar waves. It would be interesting testing - potentially dangerous - but would not really answer the question.

As I said above, if you like the benefits of a dyneema rode but think you want more elasticity you do have the option to add elasticity in the bridle. As Thinwater said we dont know if elasticity is good or bad in this particular application - there are reasons it could be good and reasons it could be bad and they may both be true in different wave conditions.

.............