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Old 03-06-2016, 02:46   #31
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Re: Para sea anchor advice

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Originally Posted by Exit door View Post
Kaptain Ken dude please don't be angry! If this is what is truly required I will pay the pennies! What I am trying to ascertain is what is the appropriate strength! If 40mm rode is appropriate then so be it.
I think I'd start with the attachment to the boat and the load that it will take and then choose a rode size. Whilst you want the rode to be able to take the load you also might consider the preferable failure mode. What's preferable, the rode breaking or it tearing a chunk out of your boat when the cleats fail.
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Old 03-06-2016, 03:42   #32
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Re: Para sea anchor advice

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Originally Posted by skipmac View Post
I don't think more and bigger cones would fundamentally change the way a drogue works, at least not as long as the cones are still small enough to be cones and not graduate to the size of a parachute.

The way a drogue works the string of cones sinks down into the water in a long catenary like an anchor chain but of course with the concave facing down instead of up. When a wave moves the boat forward the string of cones is pulled forward and upward and more and more of the cones fill.

To make a drogue work differently you would have to turn it into a totally different piece of equipment that will then no longer be a true drogue.





If I recall correctly Estarzinger deals with this issue by using dual parachute style sea anchors on very long lines.
The point is to design a different kind of anchor, not a drogue.
Fluid mechanics isn't my expertise, but I think drag is proportional to area.
So for a 20ft diameter parachute drag is something like Cd x Vsquared X pi x 400, so with 2ft diameter cones you would need 100 of them to have the same drag. To design so that there is always some of the string in the crest we could use twice as many or the same number at 3ft diameter.

The other factor is trying to get some of the string in the next crest, so it must be at least as long as the wave length, as a first approximation say 10 times the wave height, so you end up with a massive construction up to 300metres long.

My original question was does anyone know of any serious investigation of such an idea? I can't say that it would work, but equally I can't say that it wouldn't.
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Old 03-06-2016, 06:36   #33
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Re: Para sea anchor advice

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Originally Posted by Bluebeard View Post
The point is to design a different kind of anchor, not a drogue.
Fluid mechanics isn't my expertise, but I think drag is proportional to area.
So for a 20ft diameter parachute drag is something like Cd x Vsquared X pi x 400, so with 2ft diameter cones you would need 100 of them to have the same drag. To design so that there is always some of the string in the crest we could use twice as many or the same number at 3ft diameter.

The other factor is trying to get some of the string in the next crest, so it must be at least as long as the wave length, as a first approximation say 10 times the wave height, so you end up with a massive construction up to 300metres long.

My original question was does anyone know of any serious investigation of such an idea? I can't say that it would work, but equally I can't say that it wouldn't.
A far more interesting and practical idea is to use just a few smaller medium size elements. Starzinger has used 2 drogues in-line and I have tested this idea in light gale conditions. I think it is a real winner, as it eliminates the problem of a drogue pulling out of a wave face, is easier to retrieve than either a JSD or single larger drogue element, and gives more options. But I am talking about slowing the boat, not stopping it.

I will also suggest for those that have a drogue or chute and want to test it...
1. Unless you test it something will go wrong in storm conditions. It's like learning to anchor or to sail. The book cannot teach you the boat-specific stuff.
2. Test in light winds. The forces are nothing to mess with when it is strong.
3. Test in 25 knots. Light winds only teach how the parts fit together. 25 knots will begin to teach you how the lines are under tension. Open water.
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Old 03-06-2016, 07:42   #34
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Re: Para sea anchor advice

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Originally Posted by thinwater View Post
A far more interesting and practical idea is to use just a few smaller medium size elements. Starzinger has used 2 drogues in-line and I have tested this idea in light gale conditions. I think it is a real winner, as it eliminates the problem of a drogue pulling out of a wave face, is easier to retrieve than either a JSD or single larger drogue element, and gives more options. But I am talking about slowing the boat, not stopping it.
I agree with the above, but I think that the JSD has an undeserved reputation for difficulty in retrieval. I think this is due to the common wisdom that the drogue should be retrieved from the stern. On the contrary, it is really a simple matter to lead the drogue over the bow, using the engine(s) to take the strain off the drogue if necessary. When the strain is taken off the drogue it tends to sink straight down and is quickly and easily retrieved by hand over the anchor roller.
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Old 03-06-2016, 14:49   #35
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Re: Para sea anchor advice

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Originally Posted by Bluebeard View Post
The point is to design a different kind of anchor, not a drogue.
Fluid mechanics isn't my expertise, but I think drag is proportional to area.
So for a 20ft diameter parachute drag is something like Cd x Vsquared X pi x 400, so with 2ft diameter cones you would need 100 of them to have the same drag. To design so that there is always some of the string in the crest we could use twice as many or the same number at 3ft diameter.

The other factor is trying to get some of the string in the next crest, so it must be at least as long as the wave length, as a first approximation say 10 times the wave height, so you end up with a massive construction up to 300metres long.

My original question was does anyone know of any serious investigation of such an idea? I can't say that it would work, but equally I can't say that it wouldn't.
Don't know of any research on it, but since the purpose of the drogue is different, likely no one has tried it. My guess is you'd need such a long series to actually stop the boat's movement that it would be prohibitively cumbersome. I think the room needed to stow a para-anchor and a drogue might be less than the extra long drogue, but I am just guessing, never tried it.
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Old 03-06-2016, 15:06   #36
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Re: Para sea anchor advice

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I think I'd start with the attachment to the boat and the load that it will take and then choose a rode size. Whilst you want the rode to be able to take the load you also might consider the preferable failure mode. What's preferable, the rode breaking or it tearing a chunk out of your boat when the cleats fail.
No.

You fix the cleat. Obviously.
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Old 03-06-2016, 15:14   #37
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Re: Para sea anchor advice

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I agree with the above, but I think that the JSD has an undeserved reputation for difficulty in retrieval. I think this is due to the common wisdom that the drogue should be retrieved from the stern. On the contrary, it is really a simple matter to lead the drogue over the bow, using the engine(s) to take the strain off the drogue if necessary. When the strain is taken off the drogue it tends to sink straight down and is quickly and easily retrieved by hand over the anchor roller.
Please explain, step by step, how you do this. I think I'm not the only person interested. There are several steps that puzzle me.
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Old 03-06-2016, 16:20   #38
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Re: Para sea anchor advice

^^
Mike may have a clever technique that we did not think of . . but

I will comment that we tried over the bow and had two things we did not like:

(1) we liked to get underway again when the wind dropped to about 30kts. After a true storm the waves are still quite big, but also confused, at 30 kts. Neither of our boats was happy motoring into 3-5m confused waves. And (2) neither of us was happy being on the bow pulling the drogue in those conditions.

If you waited longer and the waves got much smaller then it would all be good . . . but of course it is also then no problem to pull it in by hand over the stern.

Given our general procedures and preferences we always found it just easiest to put it on a winch and crank it in over the stern. It was somewhat slow but very certain with no risk.

But there are a millions ways to do it and perhaps someone else found a better way that we never tried.
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Old 03-06-2016, 18:05   #39
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Re: Para sea anchor advice

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Please explain, step by step, how you do this. I think I'm not the only person interested. There are several steps that puzzle me.
I have only done this once, but I simply ran a line, attached with a rolling hitch, to the starboard bridle arm and around the outside of the boat, over the bow roller and to a winch. When it came time to retrieve the drogue I simply released the port bridle arm by first taking the strain with another line attached with a rolling hitch, then released the starboard arm in the same manner and allowed the boat to swing bow into the wind.

We initially used one of the primary winches, (Lewmar 48), which on my boat are located in the forward cockpit. I found, however, that the cones tended to bind in the winch and it was just easier to pull the drogue in by hand. We did not use the engines as they were not needed and my brother was able to pull the drogue quickly over the bow as I flaked it into it's bag.

Evans has had a lot more experience with these things than I do and brings up some good points. The conditions when we did this were relatively benign; 15 knots of wind with perhaps a 2 meter sea. Had the conditions been as Evans describes it certainly would have been more difficult. I wonder if, in addition to more settled conditions, we may have had an advantage in working from the more stable platform of a cat. Concerning working at the bow in rough seas, I should note that I rigged the 'trip line' prior to deploying the drogue (indeed, prior to leaving port) and we pulled it in from the safety of the cockpit, so we never actually had to go to the bow once conditions had deteriorated.
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Old 04-06-2016, 05:47   #40
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Re: Para sea anchor advice

^^ I guess where exactly your winches are located will affect the best retreval procedure. Ours were located right aft - very different from a "forward cockpit cat" configuration.
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Old 15-06-2016, 07:26   #41
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Re: Para sea anchor advice

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And your life (not to mention your boat) is what, chopped liver!!! Don't forget a small section (5' or so) of anchor chain just before the chute to keep it below the surface.

And a 5' or so beyond the chute with a float where it won't sink. It will sink; I know from experience. I deployed mine in the Gulf of Mexico back in the 80's when a Norther came in. I was single handing at the time and needed some rest after being becalmed amidst the oil rigs for two days. Anyway, after the blow was over I realized that I forgot to put the float on....It was 300 ft. down full of water.....took me an hour to pull it up...I did catch one squid in in though.
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