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Old 31-01-2010, 21:50   #16
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Originally Posted by johnar View Post
The point here is to keep the boat pointed into the weather and not stop it on a dime, every time I think of any Sea anchor I think of the Jaws movie were the shark rips the stern right off the boat.
Quoting section 6.6 of the Coast Guard Report, quote "The foregoing recommendations and discussion apply to a drogue deployed from the stern rather than a sea anchor deployed from the bow"

I suppose the choice has to do with space.
-a series drogue requires a lot of sea room as you are moving downwind more than 75 miles a day. (3-15 knots, see Fig 16 in the report)
-using a 14 ft. chute in wind speeds of 65 to over 100 knots I slid downwind about 11 miles a day, a total of 45 miles in 4 days.

I never experienced the rode (towline) going slack as the report states is the norm. Perhaps this was due to a 20 ft length of chain where the line was attached to the chute to weight it down. The chute being at depth reduced the effects of wave motion that are present at the surface.
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Old 31-01-2010, 22:30   #17
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I used our eighteen foot diameter Para Anchor International parachute sea anchor in winds around fifty knots in a winter storm north of New Zealand. Our catamaran weighs about 20,000 pounds fully loaded. At that wind level and with that displacement, the eighteen foot diameter chute worked fine.
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Old 01-02-2010, 05:37   #18
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Originally Posted by mesquaukee View Post
-a series drogue requires a lot of sea room as you are moving downwind more than 75 miles a day. (3-15 knots, see Fig 16 in the report)
I can't see the section you are referring to?

Fig 16 looks to me like just a schematic drawing of a series drogue showing the rode and cones and weight.

Perhaps you mean Fig 15, which shows a graphic relationship between velocity (ft/sec) and drag (lbs), but this does not tell you what drift rate to expect, and the graph scale is a bit odd because not many 30' boats (which the graph is supposed to be about) will sail at +10kts under full sail, much less under bare poles with a series drogue out.

Our own experience is a drift rate under bare poles with a series drogue of in +50kts is about 1.5-2kts, and with an 18' para-anchor 1-1.5kts. The pardey's have a chart showing actual drift rates for 7 different actual para-anchor situations and they are 1.1kts, 1.2kts, 1.2kts,1.5kts, 2.0kts, 2.0kts, 4.0kts. So, I don't see the difference between para and series as being so large.

I am suspecting that if you only slid 11 nm/day you had a current against the wind.
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Old 01-02-2010, 13:49   #19
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I can't see the section you are referring to?
I am suspecting that if you only slid 11 nm/day you had a current against the wind.
Caught me, the current was in the range of 1/2 knot. I slid 17 nm a day.

I meant Fig 15. which I agree does not indicate the rate of drift to expect. On reading the section which describes the mechanics of the proposed optimum conditions of how a wave passes by the boat, the comparisons of the loading on the towline, the reports estimate of how much more the load would be on a towline using a large chute one can estimate the rate of drift is 2-3 times that of a chute, it all depends on the size of the chute.

To generate a slick which is the turbulence produced by the keel of a boat you must be at an angle to the wind and drift at a rate fast enough to generate a slick. Being at an angle to the waves causes you to be pushed back faster as the forward side of the wave is essentially moving at the same rate as the wave speed (as outlined in the report). Being at an angle also increases the wind load on the boat increasing drift rate.

The report states that the tension on the towline of a series drogue is relatively constant in practice. They also state that the towline of a chute goes slack with the passing of a wave, the boat yaws and could go beam on to the seas. I never experienced that, I was always head on to the wind and seas. Perhaps that is why I did not slide back as far.
The line never going slack probably was probably due to the passing wave not having as much of an area of the hull (bow on to the seas) to push against to accelerate the boat backward. The chute was deep in the water and being so was not as affected by the back and forth motion of the water as a wave passed through it. The only force would be the slope of the wave itself which the boat would attempt to slide down on. Being a lower force the boat would be more easily pulled up that slope. A lower force does not stretch the towline as much and then accelerate the boat forward when the wave passed causing the boat to overrun the line. The line going slack would cause the chute to partially collapse which to reinflate has to dragged back some distance. Overrunning the towline would cause the boat to turn side ways to the wind and the cycle would start over.
This cycle is exactly what the report states will cause excessive loads, chaff, break towlines, tear out cleats, damage rudders or possibly result in a rollover. That is why they recommend a series drogue off the stern provided that you have the room. The report mentions a chute would be better at keeping a boat in one position if space was an issue.
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Old 02-02-2010, 06:36   #20
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To generate a slick which is the turbulence produced by the keel of a boat you must be at an angle to the wind and drift at a rate fast enough to generate a slick.
So ...... is a slick basically aerated water?
And if so couldn't pressurized water through a nozzle system of sorts do this?
Of course I'm just talking theory, but is it that type of turbulization (not a word?) of the water that makes all the difference?

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Old 02-02-2010, 06:48   #21
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So ...... is a slick basically aerated water?
And if so couldn't pressurized water through a nozzle system of sorts do this?
Of course I'm just talking theory, but is it that type of turbulization (not a word?) of the water that makes all the difference?

Extemp.
No, its a bit more complex than aerated water. Google "Von Karman Vortex" and you can see the type of turbulence we are talking about.

But realize there is a lot of controversy about whether this 'slick' really helps much in a large breaking wave situation. There is no question that the slick happens (at least with a full keel boat sliding actively sideways) and not much question that it can affect small waves. But, I at least, don't believe it has much effect on the dangerous 'rogues' - large breaking waves.
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Old 02-02-2010, 06:56   #22
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Thanks,
I'll go do some reading.

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Old 02-02-2010, 07:51   #23
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I cannot see how an area of turbulence that is perhaps 40 feet wide and 6 feet deep would have much of an effect on a wave 20-40 feet high except to perhaps smooth out some ripples in it.
Imagine being sideways to that wave if it should decide to break.
Water moving at 15 or more feet per second faster than the water in the wave striking the entire side of the topsides of your boat while your keel is being held can only result in one thing.
Having water crashing onto the deck of the boat and streaming up and over the pilothouse while not being much fun is preferable.

I suppose that there would be a lot of aerated water generated being sideways to a breaking wave.
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Old 02-02-2010, 17:05   #24
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Thanks,
I'll go do some reading.

Extemp.
Speaking of which, if you haven't already pick up a copy of "The Drag Device Database" by Victor Shane. It provides dozens of case histories in which parachutes and drogues have been used by all manner of boats as well as some analysis of the data.

Concerning different size recommendations by different manufacturers, I called the folks who recommend the larger chute and asked why the discrepancy. Their version is that Fiorentino's, being more expensive, recommend a smaller size to remain competitive. Maybe so, maybe not but I would probably go up a size if chosing Fiorentino.

Practical Sailor did a comparison of these two manufacturers a couple years back and they both did well with the edge going to Fiorentino for slightly more robust construction.

Best of luck,
Mike
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Old 10-02-2010, 16:46   #25
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I'm shortly about to invest in one or the other of these two parachute type anchors and was just about to post when I spotted this thread.

Size apart, does anyone have a real-world experience that would lead you to one manufacturer versus the other ? I'm drawn to the Fiorentino one, but I'm not sure if thats just based on the relative snazziness of their website / marketing.

The para-tech is definatley less costy especially at Defender who have it on their Miami Boat Show sale, but like life rafts money isn't everything here.

Duncan
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Old 10-02-2010, 21:12   #26
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Speaking of which, if you haven't already pick up a copy of "The Drag Device Database" by Victor Shane. It provides dozens of case histories in which parachutes and drogues have been used by all manner of boats as well as some analysis of the data.
I just don't have the time to read ALL the things that I would like to. Someone tells me this is a "must read" and I would at least get to book to read at a later date. There is so much to learn in this world! Dammit!
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Concerning different size recommendations by different manufacturers, I called the folks who recommend the larger chute and asked why the discrepancy. Their version is that Fiorentino's, being more expensive, recommend a smaller size to remain competitive. Maybe so, maybe not but I would probably go up a size if chosing Fiorentino.
You know, the same thing crossed my mind while trying to may sense of it.
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Best of luck,
Mike
Thanks!
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Originally Posted by duncan_ellison View Post
Size apart, does anyone have a real-world experience that would lead you to one manufacturer versus the other ? I'm drawn to the Fiorentino one, but I'm not sure if thats just based on the relative snazziness of their website / marketing.
Let me know if you come up with anything.
I can tell you that built heavier generally does it for me.

Good luck to us all.
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