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Old 02-06-2016, 14:00   #16
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Re: Para sea anchor advice

Victor Shane's website has some charts and he talks about sizing and forces at work. By the way, A64 you are right, chafing is something that has to be considered! The line has to go through something it is not chafing on nor will jump out of. I have not used one yet either, but I was on a large yacht that had to be towed by a freighter. We started off with nylon going through the hawse hole. That lasted maybe an hour. Then we went to steel cable. That started sawing through the hawse hole. Then we went to chain. That got jammed in the hawse hole and we ended up being towed by the strength of the hawse hole. Not good, but it didn't break. Over a million bucks for that boat but it was not set up to be towed or to take that kind of stress in line in the bow.
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Old 02-06-2016, 15:35   #17
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Re: Para sea anchor advice

I've just purchased a 16' Fiorentino para-anchor for my 45' cat which weighs in at around 20,000lb. I sought advice from the company who have spent years conducting tests for appropriate equipment. I wanted it chiefly for survival-type conditions. They recommended 5/8" rode at 10' per foot of boat length. I thought this was on the small side so I queried it. This is their response...

"The 5/8 in.rode that we use is exceptionally strong. We don't use 3/4
in. rode until we are deploying a 24 ft. parachute. You will be
surprised how well made the equipment is when you see it.... "

"450' Deployment Rode (5/8"): $1.32 per foot, plus stainless
thimbles. Commercial double braided Dacron/Nylon mix. Factory
shrunk wrap to thimble".

The rode is rated at 16,000lb breaking strength. It is just as important not to oversize the rode as this looses its elasticity and causes excessive shock loads on your hardware. I made up a bridle consisting of two 17,000lb 5/8 nylon. They recommended 45' of bridle.
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Old 02-06-2016, 15:47   #18
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Re: Para sea anchor advice

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Originally Posted by estarzinger View Post
very roughly - the rode needs to have strength equal to 60-75% of your displacement. That is to deal with loads imposed by breaking wave situations. In a 'regular' storm (eg not big breaking waves) the loads are actually pretty low - on the order of 15% of displacement.

There is a significant debate about rode material - nylon has the elasticity, BUT it generates heat while it is stretching and that weakens it - testing indicates it weakens significantly in severe cycling. And it is more vulnerable to chafe when cycling. The most knowledgeable people I know now recommend dacron for this application.
For a drogue I get polyester and agree. But for a parachute? The problem with parachutes is that they require steady pressure to keep from inverting; in effect you are towing several times your displacement in water and it does not stop on a dime. I would think going up a size on nylon would be a safer bet, to 100% disp. I think this is one of those cases of something failing because it is under strength, challenge being that the SWL of nylon is far below BS, at least 10x.
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Old 02-06-2016, 16:22   #19
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Re: Para sea anchor advice

I have an 18' para- tech if it's worth anything, they recommend nylon rode at 10 to 15 times boat length.
I believe I have 600' of 3/4 Nylon rode and 30' 5/16 chain and a monstrous SS swivel.
http://www.seaanchor.com/seaanchor.htm#rigging


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Old 02-06-2016, 17:14   #20
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Re: Para sea anchor advice

Re chafe: would a para anchor not be a good place to use a short Dyneema leader, going from cleat (or other strong attachment point) through whatever fairlead is used, and then being shackled to the main nylon or dacron rode to the chute? Seems ideal, with enormous strength, very little stretch (and hence little chafing action) and extremely good chafe resistence.

Jim
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Old 02-06-2016, 17:27   #21
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Re: Para sea anchor advice

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Skipmac,

series drogues as currently peddled as designed to function as you describe, but if you put enough surface into the water, ie more and bigger cones, then it will have the same effect as a para-anchor. I don't know how big that would have to be but there is no practical reason why not.
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.



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The potential benefit is that the drogue could be long enough to always have a significant portion in the next crest and hence keep the rode taught.
If I recall correctly Estarzinger deals with this issue by using dual parachute style sea anchors on very long lines.
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Old 02-06-2016, 18:57   #22
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Re: Para sea anchor advice

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For a drogue I get polyester and agree. But for a parachute?.
What I can say is that dashew and Yale ropes examined a number of para anchor rode failures and concluded that Dacron was preferred. In 600' length (which was recommended for breaking wave survival conditions) it still has enough stretch/elasticity and is pretty much immune to the cycling heat failure mode.

The loading is more extremely high progressive cycling, and less sudden shocks (as in ground anchoring). So the nylon elasticity provides less benefit than you might expect in this very particular situation.
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Old 02-06-2016, 18:59   #23
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Re: Para sea anchor advice

Quote:
Originally Posted by Jim Cate View Post
Re chafe: would a para anchor not be a good place to use a short Dyneema leader, going from cleat (or other strong attachment point) through whatever fairlead is used, and then being shackled to the main nylon or dacron rode to the chute? Seems ideal, with enormous strength, very little stretch (and hence little chafing action) and extremely good chafe resistence.

Jim
That seems like a great idea. Do you use one on your boat? It's one of those things I seriously consider but probably wouldn't use it too much now. With a smaller boat it may be more likely to be needed, but there is less space to stow it! (But that's for another thread!)
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Old 02-06-2016, 19:52   #24
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Re: Para sea anchor advice

Quote:
That seems like a great idea. Do you use one on your boat?
G'DAy Don,

No, we don't have a para anchor on board, but if we were to fit one, I would use such a strop at the boat end. Fairly inexpensive, easy to make, and has great benefits IMO.

Jim
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Old 02-06-2016, 20:13   #25
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Re: Para sea anchor advice

Hi Jim

Dyneema lead sounds like a great idea but as you would have to adjust your main rode you would not be able to have a fixed shackle!

I guess a bowline could fix this?

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Old 02-06-2016, 20:39   #26
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Re: Para sea anchor advice

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Hi Jim

Dyneema lead sounds like a great idea but as you would have to adjust your main rode you would not be able to have a fixed shackle!
In the real world - You actually do not 'adjust' a para-anchor rode once it is set and the storm is upon you. The loads are too high and there is too much breaking water possible on the bow to want to be doing that. At best you crawl up there and try to look that all is ok, or if you need to try to fix something.

There is no 'adjusting to wave length' - that's just a book theory. The waves are a pretty wide range of wave lengths thruout a storm. You just put out all your rode and hope it is good.

The dyneema end of rode lead is an excellent approach to reducing the chafe failure mode.
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Old 02-06-2016, 21:26   #27
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Re: Para sea anchor advice

Yeah your right Don! The reason why I want the para anchor is because I was caught in a tropical low north east of Fiji! Heaved too for 3 days! Very surfy and I was Very beamy! Went up bow and tried a drogue just to see if I could swing her in a bit! It worked a fraction! But yeah you don't want to be up there! You don't want to be messing around with rope and you certainly wouldn't be able to tye a bowline to measures�� I can see your point too on just letting all the rode out and hoping.

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Old 02-06-2016, 21:34   #28
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Re: Para sea anchor advice

Quote:
Originally Posted by estarzinger View Post
What I can say is that dashew and Yale ropes examined a number of para anchor rode failures and concluded that Dacron was preferred. In 600' length (which was recommended for breaking wave survival conditions) it still has enough stretch/elasticity and is pretty much immune to the cycling heat failure mode.

The loading is more extremely high progressive cycling, and less sudden shocks (as in ground anchoring). So the nylon elasticity provides less benefit than you might expect in this very particular situation.
And with 600' out, a few percent stretch is considerable.
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Old 02-06-2016, 21:57   #29
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Re: Para sea anchor advice

Contact Zack at Fiorentino Para-Anchor -- Manuf U.S.A

He will give you all the info you need.
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Old 02-06-2016, 22:47   #30
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Re: Para sea anchor advice

My Paraanchor came with 100 M of 3strand nylon pluse a 20 M bridle to the hain and swivel added to this is another 20 M bridled. To the bow. Have never deployed to but hope to do so as a drill soon
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