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sabray · 04-12-2013, 20:16

Oops sorry it I might not be on the web page. I read his books. He lost the drogue on a trip way north. But he says this on his page. "It was only on my fourth voyage in Mingming, after close to 12,000 miles of ocean sailing, that I was forced to deploy the JSD. This was in a severe gale off south-west Iceland on July 26th 2009, while returning from the Arctic via the Denmark Strait. Mingming rode to the JSD for 12 hours in survival conditions, and for a further 5 hours under a more conventional sea anchor. The JSD was therefore tested to the limit, not on paper, nor in a university tank, nor in someone's theoretical imaginings, but in the real laboratory of life. My personal survival depended on the proper functioning of the device; it was, literally, a matter of life and death. I also had the opportunity, caused by a silly mistake on my part that lost me the JSD, to compare its performance against that of a large single drogue". If that helps. Also note he way ovetsized the line. Means it didn't stretch at load like lesser line.http://www.thesimplesailor.com/articles.html maybe this gets to the right page where I copied this.

Geoff54 · 04-12-2013, 20:25

Thanks!
I wonder what " a silly mistake on my part" was. I'll have to see if I can track this down - I much prefer to learn from a silly mistake made by someone else than from one of my own.

Stumble · 04-12-2013, 20:28

Recommended reading...

Sea Anchor Testing with Steve Dashew and Zack Smith

http://www.para-anchor.com/reports/dashew.smith.pdf

sabray · 04-12-2013, 20:32

Quote:

Originally Posted by Geoff54

Thanks! I wonder what " a silly mistake on my part" was. I'll have to see if I can track this down - I much prefer to learn from a silly mistake made by someone else than from one of my own.

I recall it chafed on a hard shackle but might have been at the attachment. Still clearly shock loading was not the issue.

toddedger · 05-12-2013, 05:56

Thanks Stumble, good info I hadn't run across before. It eliminated any doubt for me about using dyneema.

Here is a photo of my bridal ends made up for me by West Marine Rigging.

**estarzinger** · 05-12-2013, 06:04

Quote:

Originally Posted by Geoff54

This quote is very misleading.

Hmmm . . . I have actually spoken with the people who wrote that report (as part of my role on the US Sailing Safety at sea committee). Have you? They told me that they intended the text comments in the paragraph I quoted to apply to both the single drogue types -single element (like the 4' one) AND the JSD.

They said that if anything, a JSD might have lower shock loading than a single element drogue. And so the benefit from rode elasticity would be even less with a JSD.

However, the breaking wave dynamic they described in that text applies to both the single element drogue and the JSD (with same drag surface area) so long as the single element drogue does not 'surface'. They said that the dynamics of the two drogue types were quite similar (given they are sized for similar drag surface), more similar than they expected, except if/when the single element drogue skipped on the surface. I have used both types and that is my experience also.

Can you point to empirical evidence where a JSD has failed due to chafe. If so, I think it would be interesting to know the circumstances, how it was attached and how the chafe occurred.

I know of about a dozen cases. I would say half chafed on some sort of stern gear, like a windvane; and half where the rope came aboard (not using the outboard chainplate method).

You can certainly argue that none of the installations were perfectly or completely correctly done, and the chafe would not have occurred if they had been perfect. But unfortunately little is truly perfect in the real world, and it is nice to engineer solutions which are tolerant of the most likely imperfections.

I do not know of any that have broken due to shock loading. Probably some have, somewhere, but the cases I know clearly lean toward chafe. This is also true of para-anchor rodes, where the shock loads are much much higher than on drogues. The failure mode still heavily leans toward chafe.

All of this may well be correct but an example or two does not make it proven.

Sure, but this is a problem with all discussions of drag devices. They are not used much and the results not reported or collected very well. I would suggest by any statistical or industrial standard that nylon double braid rodes are also not 'proven'.

You might remember some surprise when it turned out that those rodes experienced significant internal heat build up, and broke way less than rated strength, when used as para-anchor rodes.

But the 'mechanics' of the tape attachment are pretty clear . . .and I would suggest there is zero reason to believe it will be less secure in brait or single braid.

Note: just to be very clear. I am not suggesting this is likily to be a problem with nylon DB drogue rodes. I would guess it is not because the cycle loading on drogues is way less than on para-anchors (which is sort of the point about elasticity). I am just suggesting that none of these systems are what any industrial engineer would consider adequately "proven".

All loops are spliced and stitched. BUT, this is not proven and is just my experimental method, as yours is your experimental method.

yes, sure, I agree, everything we are doing is 'experimental'.

However, I might point out that the system we are using has been 'tested' in similar ways that Jordan tested things. Just for instance, in the tests that Stubble posted links to, on Dashew's boat, I was on board and his rode and system is identical (for the boat displacement) to ours. We tested and measured loads (note: actually speed at constant engine rpm, but it can be converted to load) at various speeds just like the USCG . And there have also been lab breaking tests conducted. I am not going to post that data here because unfortunately Zach seems to consider it proprietary (I have argued that it was/is not, but thats not a discussion for here), and he has relatively little interest in the JSD (it's a competitor to his products).

I stand by my previous post - Nylon double braid, sized according to Don Jordan’s chart, is the original, tested and proven method.

But no, I do not agree with this. Jordan's method is surely the original, but I would suggest it is also 'experimental' and not 'proven' by any scientific or industrial QA meaning of the word. There is just not a lot of experience of data out there.

As an aside to anyone thinking about this, it’s a really good ides make sure you understand the properties of any material that you are experimenting with. For example, with Dyneema , “… like all high tech ropes, it does not easily tolerate severe curves. Knotting reduces its strength more than other types of rope”. Good thing to know if, for example, you were planning to attach a dymeena loop to a ring, with a cow hitch.

Yes, it certainly is useful to understand the properties of rope and rope work . . . like when you cow hitch a apliced loop to a ring you start off with double the line strength (because the spliced loop has two legs).

Look . . . you think nylon double braid is the right solution. That's fine.

Some others of us of us, who have also both 'tested' and actually 'used' our systems, think while Nylon DB it is perfectly adequate, it is perhaps just a bit more difficult to stow and more chafe prone (in the installation is not perfect) than other alternatives

All my posts here have been intended to suggest/explain the trade-offs so the OP can make his own decision.

Zanshin · 05-12-2013, 06:22

I haven't used my 132-cone self-built drogue in anger, but feel that the elasticity is important and that double-braid is going to be cheaper and easier to work with than a plaited line.

**estarzinger** · 05-12-2013, 06:49

Quote:

Originally Posted by Geoff54

You know nothing about me – please do not presume to know what I have or have not done.

By the way, I apologize if I offended you. I was simply trying to clearly explain my understanding of the facts. But on the internet "clear" often gets (miss) interpreted as offending.

Just FYI, I played a leading role in writing the ISAF recommendation on drogues and para-anchors (for offshore racers). As part of that, I spent quite a bit of time with the USCG, and other bodies that had conducted tests (like the Wolfson unit - they have published some good test, if you are interested in the subject).

**estarzinger** · 05-12-2013, 11:03

very slightly off topic . . . but completely relevant . . . .

My current boat really likes a drogue, and I have tried all sorts of different systems (different drogues and different rodes).

My favorite system today is a "2-element series". I use two single element drogues in series. I first put out a dead stock galerider, when I want a little extra steering control and a little speed reduction/smoothing. Then when I feel a need for a little more control and speed reduction, I have a delta drogue I modified so that it has a dyneema strop thru its center with thimbles. I attach the 'back end' of this drogue to the tail end of the rode that is out, and another rode to the front end and let it out. So, in the end, I have the galerider, and a rode and the delta drogue and a rode and then the boat. (BTW, I now use dyneema 'soft shackles' to connect the bits together)

This has many of the JSD advantages over the single element drogue, most particularly that the two elements will never skip at once. And it has many of the single element drogue advantages over the JSD, most particularly (a) it is easier to recover with no somewhat fragile cones to break, and (b) it does not require a dedicated rode (like the JSD does).

This hybrid has seemed to me to be the best possible system, including the advantages of both the single element and the JSD. But, I will say that while we have now used the hybrid in quite severe conditions, they have not been survival conditions. So, while I have gained significant confidence in it, is still 'untested' in the worst case.

Now, bringing it a little back to the thread topic. This hybrid does not require a dedicated rode, and you can use any line you have on board. I carry several spare nylon anchor rodes in multiple constructions (brait and double braid and 3 strand), and I carry several floating shore lines in both polypro (a four strand commercial fishing construction) and dyneema single braid, and I carry a bunch of sailing line in dacron and dyneema double braid. I guess I have not tried every possible combinations of these lines, but I have tried quite a few and I see/feel little difference in their effect. What I have settled on for this hybred is really more for convenience that particular fiber functionality. I have two nylon DB anchor rodes, which have thimbles spliced in, in tall mesh bags, stowed immediately available the Laz. I use those for the two rodes as they are simple the most convenient lines the way I have the boat stowed (note these are also the lines I would use for the para-anchor rode). Then I use two spare 75' dacron sheets to form the briddle. Again, on passage they are stowed to be immediately available. That works well, so, as I said several times above, nylon functionality is certainly acceptable, but I am here I am using rodes that have other primary purposes (anchor and para-anchor) and they HAVE (IMHO) to be nylon for those applications. If it were a dedicated rode, only for the drogue, I would use dyneema, as I have done for the JSD.

And just to continue a tangent . . . a bridle is very important, putting the pull centered behind the boat. If you try to run it with only a single rode off one corner, it will effect the boat steering negatively, especially when hit by a breaking wave, or going off the top of a steep one.

**estarzinger** · 06-12-2013, 13:44

By the way, there is a "clever" way to reduce both the size and expense of a JSD rode.

The key observation is that the load varries along the rode - very small at the tail end where it is only pulling a couple cones, and high near the boat where it is pulling the full set of cones.

So you can tailor the rode to the load by "tapering" it.

There are sophisticated ways to taper it, but the simplest it to divide it into 2 or 3 sections and use two or three different diameter lines, smaller toward the end.

We did this with our dyneema rode, using two equal sections - a smaller (1/2 strength) for the tail section and a larger (full strength) section closer to the boat. With single braid it is easy to do a very slick end to end splice to join the sections. For other constructions cow hitched eye splices would probably be the way to go.

To give due credit . . . I believe the guys at Ace sails pointed this out to me.

thinwater · 06-12-2013, 14:08

Quote:

Originally Posted by estarzinger

... My favorite system today is a "2-element series". I use two single element drogues in series....

While I've never had to use a drogue in survival conditions--I'm a coastal sailor and they aren't too hard to avoid--I did find my self in the wake of a huricane once in a bit more wind than I had hoped for. We were doing fine, running with just a little bit of jib, but my crew had rumbly tummies, so I thought I would experiment with the drogue to quiet the ride. It was blowing ~ 35 plus gusts with 10' waves, according to NOAA.

I have a single Seabrake. I deployed it with 15' of 3/8" chain, 150' of polyester double braid, and a very short bridle. Slowed us down nicely, bu the boat still yawed, as the waves and the wind were from somewhat different directions. Then, as per the plan, I let out ~ 75' of bridle, enough that a good portion was in the water, specifically when a wave would come up behind us. The long bridle gave us some breaking force closer to the boat (less tendency to surf) and some directional guidance (less yawing) as well. In someways like having a second drag element closer to the boat, a towed warp that cannot pull out of the wave because it is held down by the drogue further back.

So, I wonder if some experimentation with very long bridles makes sense.

The heating subject is interesting too. Because bridles tend to be one size smaller than the bridle, they are not subject to as much heating, thus in principle, long bridles are the safe place to absorb energy. In a real worst case storm, perhaps a smart plan would be to use a non-heating and non-fatiguing line such as Amsteel for the main rode, coupled with very long nylon bridle lines. The bridle lines could even be set up as spares, so that if one breaks it can be replaced mid-storm; I'll leave it to others to think through the possibilities.

As for what the Jordan report said for line type, if he did not specifically criticize non-stretch line and explain the problem, it might well be that he simply did not investigate that variable. He did a lot of work, but they did not investigate everything. We owe him much, but he would want us to try and move the ball forward.

DumnMad · 06-12-2013, 14:34

Interesting thread. Dyneema looks to be a clear winner.

Energy absorption will be by the vessel dragging of the SD through the water and increase gradually as the wave accelerates the boat forward. Nothing like the impact load of a moving vessel being stopped by an anchor fixed to the seabed. However it would still be nice to know that the fitting was stronger than the expected maximum load on the rode.

Stumble · 06-12-2013, 15:02

Quote:

Originally Posted by DumnMad

Interesting thread. Dyneema looks to be a clear winner.

Energy absorption will be by the vessel dragging of the SD through the water and increase gradually as the wave accelerates the boat forward. Nothing like the impact load of a moving vessel being stopped by an anchor fixed to the seabed. However it would still be nice to know that the fitting was stronger than the expected maximum load on the rode.

For a typical 40' cruiser in the 20,000lbs displacement range JSD has a max design load of 13,000lbs. Which would require...

3/4" nylon brait
5/8" double braided nylon
1/2" endurabraid (really 12mm)
5/16" amsteel blue

A fitting that strong would take some serious backing plates. Assuming a bridle splittingt the load in half that is still 6,500lbs per leg, or roughly triple what a normal winch would be rated at on a boat this size (just an example I know attaching to winches is a bad idea).

DumnMad · 06-12-2013, 16:32

The 13000 lbs (6t) is the breaking strength presumably with a high FOS for wear & tear. Assuming a bridle then actual loading might be lucky to get to 1ton each side. In 1 inch plywood; a couple of 1/2 inch bolts with a good backing plate.