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Old 01-12-2011, 12:28   #61
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Re: Series Drogue on a Production Boat ?

I think Don Jordan was designing for survival conditions where the boat was out of control (extreme weather, crew exhaustion, gear failure etc) and at serious risk of being knocked down by a breaking wave. The series drogue design is therefore the equivalent of a parachute in an aircraft. He concluded that to guarantee survival in virtually any conditions, you have to restrain the boat in the water somehow but with out breaking anything or jerking, and you had to keep it from turning beam on to breaking seas.

The idea is not to slow the boat down for steering purposes. The drogue allows the boat to move slowly because to try and stop it in the water would increase the forces involved unacceptably...which is why a parachute anchor off the bow is not advised in extreme conditions..it is too rigid. Jordan said that the way to use the series drogue was to deploy it, lash the wheel midships and go below and rest/sleep. There was nothing more that could be done that would improve survival chances. On deployment, things calm down dramatically, possibly because the drogue keeps the boat 'sheltered' in the troughs more than would otherwise be the case? You would not want to move fast under these circumstances unless you had miles of sea room and no lee shores in range!.

I've not heard of any cases of serious pooping by being restrained from the stern by a series drogue. It would be good to hear from anyone who has.

If you want to slow down in non survival conditions, then warps or galerider type single drogues are fine. The idea of having two series drogues is OK but you'd never be able to switch from the 'small one' to the big one without cutting away the small one as you'd not be able to retrieve it in severe conditions and you could not have both out as they'd tangle up. Adjusting the length of a series drogue depending on the conditions sounds feasible but difficult to implement due to the huge forces involved. As mentioned, loss of fingers etc....!
The comment above about the bridle snagging davitts is worth taking seriously!
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Old 01-12-2011, 14:47   #62
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Re: Series Drogue on a Production Boat ?

Why not just do like Evans does... link a few Delta drogues together? It would be much easier to pull in, stores in sections, easier to make, and still keep at least one of the drogues in the wave. I could see using three smaller 36" drogues spaced 50' apart on a long lead.

I have seabrake for my boat, and it did a great job when I tested it out in 15kts, but thankfully haven't been in anything that really needs it deployed.
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Old 01-12-2011, 15:55   #63
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Re: Attaching a series drogue...

Quote:
Originally Posted by Boracay View Post

It would be interesting to ask the designers of some modern production boats if any attachment point that could actually be installed would be able to take that sort of load.
The breaking strength of cleats are in Hunter manuals, not sure of other builders.

This is for a Hunter 33:
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Old 02-12-2011, 10:34   #64
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Re: Series Drogue on a Production Boat ?

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Originally Posted by Bash View Post
That goes for any drogue. You won't understand that your davits are in the way until you've launched the drogue. Best to make such discoveries before you really need the drogue to work.
I took off the davits for other reasons. But as the metal pads they were bolted to now carry a deck crane and a wind gen pole, the same argument holds...if your bollards or cleats are in conflict, you have to rethink the bridle size, or if push comes to shove, make the gear hanging off the stern of the "quick-release" type.

Or you'll have to install dedicated (and massively backed) cleats or bollards for the drogue, which could double as towline attachments in calmer weather. Maybe that's the best solution.
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Old 02-12-2011, 10:42   #65
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Re: Attaching a series drogue...

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The breaking strength of cleats are in Hunter manuals, not sure of other builders.

This is for a Hunter 33:
One of the prime reasons I have a sort of sneering reaction to boat show salesfolk claims of "Lloyd's Ocean Class A" certification is that many modern production boats feature glassed in pads with cleats screwed into them, as opposed to through-bolted with load-spreading and preferably metal backing plates extending as far as is practical.

A lot of "offshore-capable" models also sport 24 inch lifelines, but I won't get on a rant.

After even minor gales on Lake Ontario, it's not wildly uncommon to see a cleat torn out of a deck on a modern production boat, and while this could be attributed to bad dockline management or other operator error, I am not persuaded that it isn't simply a "Rocna tactic" to spend and do less in the cleat department in order to save a few bucks and to keep water out of the boat by not putting holes in the deck in the first place. I understand that, but I can't justify it. A dry boat with weakly mounted cleats will bite you some day.
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Old 02-12-2011, 11:17   #66
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Re: Attaching a series drogue...

Quote:
Originally Posted by S/V Alchemy View Post
One of the prime reasons I have a sort of sneering reaction to boat show salesfolk claims of "Lloyd's Ocean Class A" certification is that many modern production boats feature glassed in pads with cleats screwed into them, as opposed to through-bolted with load-spreading and preferably metal backing plates extending as far as is practical.
I was quite impressed with the cleats on my tupperware boat, although not the most massive of scantlings, the cleats are through bolted with large "fender" washers backing.
I've just fabricated two backing plates made from 6mm stainless plate(ex vanes from a very large hydraulic motor), which I will use under the aft cleats as extra security.
If I go for a JSD in future, I'll be bolting on dedicated securing points which will overhang the transom slightly, again, using the hydraulic motor vanes.
Good point made by Bash about davits etc, I've made sure that the ones I'm fitting will not foul anything, well, not unless the boat ends up at 90* to the drogue, if that happens, I probably wont be in a position to care anymore
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Old 03-12-2011, 07:51   #67
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Re: Series Drogue on a Production Boat ?

A prudent move. While the fender washers are fairly standard practice, on deck-mounted standing or cheek blocks, or cleats for that matter, sideways pulls can deform the fenders, causing them to "dish" or go a bit concave. I replaced most of mine with (in my case) 1/4" aluminum plate, circular for under the winches the cheek blocks and rectangular elsewhere. After tearing up a genoa track in a gust, I did the same "rebacking" in that area, as well. The key, if the deck is cored, is to isolate the core with an epoxy donut in each bolted hole. A careful bevelling will allow sealant/bedding material to truly keep the water out, as will applying a small amount of bedding on the bolts themselves and on the perimeter of the backing plate. Bolt just beyond finger tight at first and then go for a dogging down 24-48 hours later for best results.

I can't recall precisely where I saw this, but I believe it was in a Hal Roth book where he describes setting up special cleats for a drogue or warp, and he did something very much as you describe for the transom: fairly massive load-spreading stainless plates backing dedicated cleats or hard points (they might have been large padeyes) that seemed like overkill until he actually put them to the test!
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Old 03-12-2011, 14:50   #68
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Re: Series Drogue on a Production Boat ?

I can't find it anywhere. But I am sure somebody knows.

What is the rule for the length of the line for a drogue (from the stern)

Not the load or diameter just the length

Thanks
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Old 03-12-2011, 16:20   #69
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Re: Series Drogue on a Production Boat ?

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Originally Posted by SvLetitgo View Post

What is the rule for the length of the line for a drogue (from the stern)
There's no hard and fast rule, but 300' is a good general purpose length.

'have the drogue two waves back" is one thought, which obviously depends on the wave length.

For a series drogue one rule is: bridle = 2.5 x beam + 75' leader + 20" per cone (number of cones depends on boat displacement). More discussion here. Generally these come out to 300' or a bit less.

For a single element drogue most people just use what ever they have for stern/spare anchor rode, which is usually around 300'.
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Old 04-12-2011, 10:59   #70
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Re: Series Drogue on a Production Boat ?

I've heard some variation, too, over the utility of putting any kind of chain or other weight on a JSD at the far end. My sense is that it's considered unnecessary as the design itself should keep it from "skipping" out of the water for any more than a short portion of its length.
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Old 04-12-2011, 11:04   #71
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Re: Series Drogue on a Production Boat ?

Tank you so much for your answer Evans.

Would Polypropylene be a problem or it would work as well. As this is what most of us have for Stern line.

We are talking single drogue with a bit of chain to weight it down.
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Old 04-12-2011, 11:42   #72
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Re: Series Drogue on a Production Boat ?

Quote:
Originally Posted by S/V Alchemy View Post
I've heard some variation, too, over the utility of putting any kind of chain or other weight on a JSD at the far end. My sense is that it's considered unnecessary as the design itself should keep it from "skipping" out of the water for any more than a short portion of its length.
I've never used a JSD, but I went through all of the reports, etc. on the Coast Guard tests, tank tests, and Jordan's original write-ups on it. All easily available on the interweb and very informative.

My understanding is that the weight on the end has nothing to do with skipping out the back of waves. It's there to prevent shock loading of the transom. As the boat goes up the wave, the force on the JSD is reduced and the weight sinks the JSD to a vertical position. When the boat crests the wave and tries to surfing down the other side, the JSD becomes horizontal gradually, and this reduces the shock on the system, letting it survive a long storm.

It's actually an amazingly simple way to reduce the shock loads. I can't think of any reason not to use the JSD as the designer had intended. He tested the heck out of it. When I make mine, it'll certainly have the weight on it.
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Old 04-12-2011, 12:42   #73
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Re: Series Drogue on a Production Boat ?

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Originally Posted by estarzinger View Post
For a single element drogue most people just use what ever they have for stern/spare anchor rode, which is usually around 300'.
Polypro, of course, is a bad idea. The physical properties are not there and it floats (you want the drogue buried).

However, for the JSD, the makers actually allow high-modulous fibers, as they save weight and do not effect the onset of drag in an important way. Since the cones are spread over a long line, the impact absorption is inherent.

The makers of the Seabrake drogue suggest polyester rope, as nylon stretches too much and delays the build up of drag too long.
http://www.seabrake.com/pdfFiles/Sea...uctionCard.pdf

Nylon is required for parachutes in order to steady the load.

Towed warps are always "whatever you've got", and like the JSD, the material (other than polypro) will make little practical difference. Wieght and spread are what matter.

I did some testing, to see how the devises relate:
Sail Delmarva: Drogue and Parachute Sea Anchor Testing: A Summary for Small to Medium Cruising Catamarans
Not storm testing--I'm a coastal sailor and avoid big storms. I did use a chute in a very nasty squall once on a 1200-pound 27-foot cat, though, and that expereince (not unpleasant) gave me a few ideas.
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Old 04-12-2011, 16:53   #74
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Re: Series Drogue on a Production Boat ?

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Originally Posted by SvLetitgo View Post
Would Polypropylene be a problem or it would work as well. As this is what most of us have for Stern line.

We are talking single drogue with a bit of chain to weight it down.
The Deshews and we have used spectra for our series drogue rodes, to greatly reduce the weight and bulk. Spectra floats but does not seem to hurt the series drogue performance.

I have always used nylon (double braid) for our single element drogues (and our experimental 'few element series'), so can't comment directly/first hand on how polypro would work. My guess is with a bit of chain to sink the drogue it would work ok. If the floating caused any real problem you could add or tie a short section of chain to the middle of the rode to sink it.

You could take it out and tow it and see if the drogue sinks or tends to surface/skips on the surface, but this only gives you a 'better guess' because the performance/behavior of drogues can be quite different in big steep waves than in flattish water.

The quality of polypro rope varies quite a bit - there's some really shitty stuff and some quite good stuff and the price different between this is not that great. We found some terrific polypro in a commercial fishing chandlery in Cork (Ireland) and bought our shore lines for Chile.
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Old 04-12-2011, 18:34   #75
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Quote:
Originally Posted by w1651

According to Hal Roths book Cruising around the world. You must have a line connected to two points at the stern(which also means a good connection point to the boat). You also must make this line 16 to 18 times as long as your stern is wide. So if your stern is 5 ft wide then the line should be 90 ft long attached to the stern at each end, and the drogue attaches to that line at the center.

Here is the coast guards report on the Jordan series drogue

http://www.jordanseriesdrogue.com/pd...uardreport.pdf
Many thanks for that link. It is a great read and lots of nuggets in there. It certainly got me thinking about changing my paradigms. Most significantly is the "sea anchor" (bow to) and "drogue" stern to.

One nit and one question for those that have taken the time to read the report.

The Grimalkin ended up not sinking - OK that's a nit...

In the report, probably in the summaries and conclusions there is a statement that the series drogue is the better system, stern mounted is the better system for fin keel boats!!!

I am now thinking for a "full keel" boat that is hit from behind at any significant angle, would the turning moment of the passing wave on a full keel vs. fin keel have a significant impact on the longitudinal stability of the boat?

PS - It was really interesting to see this circa 1986 report with basic computer code provided in the apendicies for describing wave plots. Too funny...
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