Para anchors not the whole truth

[bryanglover]

para-handy
There is not anything like the same loads placed on a drogue as there is with a para anchor, because vessel is not held to station but continues to move thru the water, building up speed with the wave, slowing down with the drogue.
Also a lot of us now believe that double braid nylon is not the best line for para anchor or series drogue, because line achieves high temperatures which appears to weaken rope. single or double braid polyester is being talked about, as a better option.

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[Birdseye]

I read the USCG report some years ago, and it seemed to me that a credibly scientific approach had been taken with quite a bit of tank testing both of monohulls and a model tri. The case given for the series drogue was reasonably convincing, but you have to accept the impracticality of ever getting a definitive answer on a question like this. Tank testing is OK but it can never repeat the variabilities of real life. But then those variabilities make real life experiences relatively meaningless too. How useful is the Pardy's experience if you are different, sailing a different boat, in different seas etc?

It's intriguing that the USCG report was done by the inventor of the series drogue. That doesnt necessarily disqualify it to my mind - there are such things as honest men. Belief is not the same as bias. But it does naturally raise some doubts. Not suggesting it has happened in this case, but I have seen UK govt quangoes bend to political pressure to promote UK products.

I have actually seen a para anchor work very effectively with a Prout Snowgoose in a 70kn squall off N Spain. Unfortunately, they failed to recover the anchor - perhaps should have waited longer since the wind was offshore. The two people aboard spoke highly of its effectiveness on a bridle from the bow. Nevertheless, If I were in the market I think I would go for the drogue from the stern because the arguments are more convincing. My worry would be resistance of the boat to pooping - a point made in the USCG report

<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.

 

[bryanglover]

Birdseye,
I can't recall the coast guard having problems with pooping, They do say the following.


“With a series drogue deployed, a well-designed and properly constructed fibreglass boat should be capable of riding through a Fastnet type storm with no structural damage. Model tests indicate that the loads on the hull and rigging in a breaking wave strike should not be excessive.
1. Many sailors are reluctant to deploy a drogue from the stern because they fear that the boat may suffer structural damage if the breaking wave strikes the flat transom, the cockpit and the companionway doors. The model tests do not show this to be a serious problem. The boat is accelerated up to wave speed and the velocity of the breaking crest is not high relative to the boat. The stern is actually more buoyant than the bow, and will rise with the wave. However, the boat may be swept from the stern. The cockpit may fill and moving water may strike the companionway doors. The structural strength of the transom, the cockpit floor and seat, and the companionway doors should be checked at a loading corresponding to a water jet velocity of approximately 15 ft./sec.
2. When a boat is riding to a series drogue no action is required of the crew. The cockpit may not be habitable and the crew should remain in the cabin with the companionway closed. In a severe wave strike the linear and angular acceleration of the boat may be high. Safety straps designed for a load of at least 4g should be provided for crew restraint. All heavy objects in the cabin should be firmly secured for negative accelerations and drawers and lockers should be provided with latches or ties which will not open even with significant distortion of the hull structure”.
U.S. Coast Guard Report CG-D-20-87 sec 6-4

Bryan

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[Mirelle]

That has been my experience, anyway

I have no experience of parachute anchors, but a normal drogue spins like a top, as soon as any load comes on, and would certainly frap up a tripping line, unless, possibly, as shewn in some seamanship books, the tripping line is buoyed ar regular intervals and the drogue is weighted. But that seems an awful lot of trouble to go to, and not wholly reliable anyway.

I did think, the first time it happened, that the spinning was down to the three strand warp, but on trying again, long afterwards, with braided warp, it spun just the same - I think it is just a way of the drogue trying to dissipate some energy.

You can get an un-tripping-line-equipped stern drogue back by putting a rolling hitch on the warp, leading the relieving line forward outside everything, taking strain on it with the windlass and casting off aft; it is then feasible to sail or (carefully!) motor up to the blighter. But I reckon the temptation to cut them adrift is pretty great - if I had not made mine myself, so that I knew how many hours had gone into the thing, I would have cut it away.

<hr width=100% size=1>Que scais-je?

 

[Jools_of_Top_Cat]

Spinning

That said, would it be prudent to fit a swivel at the drogue then to protect the line?
How long would a series drogue spin before the rode parts?

I do not have a drogue nor para and find this very interesting reading.

<hr width=100% size=1>Julian

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[BrendanS]

I think some of my major concerns are that the author has published several notes on the use of serial drogues, not based on his own experience, but on the use in real life of people who have bought, or more usually manufactured, their own serial drogues. This type of communication, while interesting, and bringing up several practical issues, does suggest anecdotal rather than well researched and founded in fact

If anyone is interested, quite easy to find by googleing on .... donald jordan drogue

<hr width=100% size=1>Me transmitte sursum, caledoni

 

[zefender]

Er, I'm no expert on this but I'm not convinced many of the first hand experiences outlined by the Pardeys are very relevent to modern (fin) boat designs. Also, given the litigious nature of the US, I don't suppose it's CG would issue any advice that it wasn't pretty confident about.

If I remember correctly, Pardeys suggest that 'active sailing' of light, modern fin boats is probably the best strategy - assuming sufficient crew strength. But most of their experiences of a para anchor were on long keeled heavies. Assuming survival conditions, I think I'd feel more at ease about trailing something to slow me down whilst keeping some steerage, rather than having to take pretty much everything on or near the nose. As for recovering the thing, if it really were survival time, I'd be inclined to just cut it loose! The only thing that slightly concerns me about a drogue is the worry that if the wind were to change, then I could find myself going downwind, with the waves created by the earlier wind crashing along my beam or least the presence of the drogue limiting options as conditions change slightly. One of the useful bits of advice from the Pardeys (if I remember) was that the most dangerous time is immediately after a storm when the wind has abated but the sea is still very lively.

As for the original point of the post about claims in advertising re para anchors, it would be very hard I'd have thought to hold back advertising for a product on the basis of innacurate claims. Maybe a para anchor is the best solution for the right type of boat, in the right type of conditions. Maybe auto-inflateable lifejackets are useful things to have on board - but are they actually safer than a permanent, foam based jacket? So should they be advertised? Are CQRs better than danforths? Should only one rope cutter product be allowed to be advertised as 'truly effective or 'best'' just because some expert says it is? I've driven some fabulous cars that have been slated on Car progs on TV and mags and have often disagreed strongly with some of the reviews of products in the yachting press. I think I prefer caveat emptor.

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[Mirelle]

Re: Spinning

I dunno; it just seems to spin one way and then the other; my impression is that it is just spinning to dissipate energy and I don't think it harms the rope; once it has gone far enough one way it reverses, because there is no special reason for it to go one way or t'other.

<hr width=100% size=1>Que scais-je?

 

[AndrewB]

RORC trials of series drogue

What convinced me about the series drogue was not the USCG report, though I do not share your lack of faith in it, but the film of the RORC trials conducted by the Wolfson Unit in their tank at Southampton. Has anyone else seen this film? It is impressive. Model yachts towing a Jordan drogue comfortably hold steady to a breaking wave when those 'running before' without simply broach and roll. The testers estimated that it took a breaking wave over twice as high to roll a yacht with a drogue. Of course the yacht will be pooped: we are talking proper sea-going yacht designed to cope with this sort of thing, not a BenJenBav.

Unlike Brian Glover I hold no commercial brief. My drogue is home-made to the USCG recommended design.

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[zefender]

Re: Huh?

"Of course the yacht will be pooped: we are talking proper sea-going yacht designed to cope with this sort of thing, not a BenJenBav." ....

So 80% of boats are not proper sea boats then - bit sweeping praps?


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[AndrewB]

Re: Huh?

Apologies, I should have said ocean-going, or at least likely to go far enough away from land that riding out a prolongued gale on a sea-anchor is a real possibility. The vast majority of yachts are designed, intended and used for coastal sailing, even if the advertising blurb tries to create the impression that their horizons are unlimited. Plainly modern build quality means that even boats not designed for ocean cruising nevertheless do successfully cross oceans, particularly on the easier trade wind routes. But I would stick by my assertion: these yachts are not designed with the expectation of sailing downwind in open ocean in large breaking seas. A large, poorly drained cockpit, low bridgehead, high hull windage, lowish AVS, low directional stability, a rudder not firmly supported at its bottom edge, light rigging and in-mast mainsail reefing are all going to be liabilities in such conditions.

 

[zefender]

Re: Huh?

I think so many of these modern designs have been whizzing round the oceans for so many years that we would have known by now if the situation was as bad as you say. I agree though that the rudder is vulnerable. However, most of these large cockpit boats have open transoms, which is a pretty effective way of getting rid of the wet stuff. Not sure how high hull windage would matter much (might even help) when sailing downwind.

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[bedouin]

Re: RORC trials of series drogue

Yes - I know of those tests and I agree that the series drogue is an effective device in the right circumstances.

My real objection to the USCG is the fact that it wrote off parachute sea-anchors without even bothering to test them - not the mark of a serious piece of scientific research.

In fact I carry a conventional drogue, and agree that a series drogue is probably better, but all my sailing is coastal/offshore where I think a sea-anchor is never likely to tbe the appropriate solution. However if I were equipping my boat for ocean cruising a parachute sea anchor would be higher up my shopping list than a series drogue

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[AndrewB]

High hull windage.

Is it really true that "most of these large cockpit boats have open transoms"? If so isn't that another definite minus, increasing the exposure of crews in bad conditions.

High hull windage will encourage the yacht to go faster downwind, e.g. under bare poles. Though it is possible by active steering and some skill to manage this, it is very undesirable for a passive policy in strong winds, which most shorthanded crews will prefer to adopt. Also, I would guess that high windage is more likely to lead to a roll following a broach.

Actually I think we do know by now that these medium sized AWBs have limitations for extended cruising. This is why insurers have been getting increasingly nervous: not because lives are being lost, but at the number that suffer expensive damage from the elements.

 

[bryanglover]

Re: RORC trials of series drogue

Bedouin
Your assertion that the coast guard discounted para anchors on a whim is incorrect.
The Coast Guard completed two studies, the first was in regard to existing tactics, one of which was para anchors, from this first report they concluded that para anchors were not capable of saving a yacht in breaking wave situations, such as the fastnet race.
report cg-d-20-87 was the 2nd,
Bryan

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[Guest]

Post deleted by danfoley

 

[bedouin]

Re: RORC trials of series drogue

The report comes to conclusions such as "Series Drogues are better than Para-anchors" without giving any write up of the tests they carried out on the para-anchor. As any scientist will tell you that is total nonsense.

So as a piece of scientific work the paper is useless.



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[PaulJ]

...and while we\'re on the subject........

Has anybody tried a "one ton bag" as a drogue? My local building supplies sells them for £3.50p, they are about 4ft in Diameter and I would have thought, quite strong enough. I don't know if it would remain open if used as a drogue or if perhaps it would need a couple of stout bits of wood with a bolt through the middle and opened out as a cross to hold it open? The whole thing should cost less than a tenner so if you did have to cut it loose it wouln't be a great loss..... as long as it didn't subsequently get caught round someone else's propeller! Perhaps you could attach a hefty weight to one attachment loop which would ensure that it sinks but may also stop it spinning?

I'm afraid my boat still isn't quite finished or I would try it myself..... any volunteers?

<hr width=100% size=1>I used to have an open mind but my brains kept falling out.....

 

[cliff]

Re:Has anybody tried a \"one ton bag\" as a drogue?

Yes and I don't recommend it. Too, too much drag.

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[PaulJ]

Re:Has anybody tried a \"one ton bag\" as a drogue?

Cliff, Thanks for responding, what size was the boat you tried it from and what were the conditions like? Did it stay open by itself or did you have to keep it open with something?

<hr width=100% size=1>I used to have an open mind but my brains kept falling out.....