use of drogues

[Guest]

Where is the best place to look for advice on use of drogues?
Should the drogue have a marker/flotation buoy?
Should a swivel be fitted, which end?
Does the tripping line merely go to the surface to a buoy, or is it brought all the way back to the boat?
How do you calculate the strength and length of warp required?
My boat is a 32 ft Rampart, about 7 tons, a motor boat with mizzen.
Opinion in books seems sharply divided, but it seems prudent to carry one in a single screw, round bilge, non-self draining cockpit boat.
Grateful for any advice.
Pilot

 

[webcraft]

The most comprehensive information is at

http://www.sailrite.com/drogue_information.htm

Info on the Jordan series drogue at
http://www.acesails.com/

Info on the para-tech Delta drogue at
http://www.seaanchor.com/deltadrogue.htm

Hope this is some use,

Nick




BlueMoment.Com
http://www.bluemoment.com

 

[LadyInBed]

Re: Drogue Size

I found this formula for the size of a drogue
Mouth Diameter ( D ) = 8.5 cm per meter LWL
Length ( L ) = 1.5 D
Tail end diameter ( d ) = D/8
Distance from ( D ) to where 4 lines come together to a towing point is equal to ( D )

Any comments?

 

[LadyInBed]

Also see . . .

drag device data base
http://www.dddb.com/

 

[charles_reed]

Appears a degree of confusion between drogues and sea-anchors.

Sea-anchors arouse strong feelings: 50% of "authorities" condemn them as dangerous, 50% swear by them being the answer to all ills (notably the Pardeys).

For a 10m boat a para-anchor is about 3.6m dia.
A drogue for the same boat is about 0.75m dia.

Whilst para-anchors arouse fierce contention, drogues are, almost universally accepted as "a good thing" and, probably the best design is the standard RNLI issue.
This is made of heavy canvas with an aspect ratio of about 4:1, chain rigging lines and a heavy swivel, before the rode which should be nylon with enormous chafe-protection.
Again for a 10m boat you're looking at about 10mm dia upwards.

Be aware that when wet nylon, due to hysteresis heating can lose up to 40% of its dry SWL.

I carry drogues, preferring 600mm x2 in tandem rather than a large single one. I can also deploy one on each qurter for steering purposes (much more useful than storm-work).

The reference to a tripping line almost certainly refers to a para-anchor - the problem with tripping lines is that they always seem to wrap round your rode, and don't do the job when you want them to trip the chute.

In a nutshell, a paranchor is ideal, allowing crew to save themselves for the struggle to come, during the early part of a storm (>F10) when wind-force is high and seas building - during the latter stages, when wind is dropping and seas are at their worst trying to recover it is a bastard.. far better to cut it loose.
I find one can do the same by heaving to, up to about 50 knots/wind, when my boat forereaches at about 60 degrees to the wind.
Before deciding what you're going to do try some of the older, proven approaches and try the things out - trouble is F7 is no substitute for F10 and who is going to put their head in the proverbial lion's mouth?

 

[vyv_cox]

Good post, Charles.

For me, the main reason that the Pardeys' method attracts such a lot of criticism is their suggestion the the boat be attached from the forward quarter, rather than the bow. Thus the boat lies at an angle to the waves, rather than head to them. Many of us will have some experience of lying beam to wind, current or both and will have experienced the enormous force that this applies to the warp. Leading the warp over the bow seems a far more logical way to deploy a para-anchor, although I confess my thoughts are purely theoretical!

There is quite a lot of information and case histories at http://www.dddb.com/index.html

 

[ccscott49]

I agree with you, the only time I drag my anchor, is when the boat turns broadside on to the wind, then the force is enough to dislodge the anchor, the boat then stays that way, as is narural, continuing to drag the anchor sideways. Showing the forces are higher when the pull is broadside. Which I guess is obvious, giving the windage broadside on!

 

[bedouin]

One of the best sources of information about heavy weather is "Heavy Weather Sailing" by Peter Bruce. That includes some useful information about sea-anchors, drogues &c.

Although there is a lot of information out there, a lot of it is prejudiced towards one point of view or another, so should be taken with a pinch of salt.

The Pardey's book is the definitive work on parachute-type anchors. Their system is tried-and-tested and works for them. However as others have said there is not universal agreement about this!

It is worth pointing out that the Pardeys sail a 29' long-keeled boat - and many of the other supporters of this approach seem also to be experienced in smaller boats. The forces on a sea-anchor, even on a small boat, are tremendous and increase in proportion to the weight of the boat - what works well on a small boat might be totally inappropriate on a bigger vessel, I feel this may be the cause of a lot of the controversy surrounding the methods!

 

[PaulJ]

The most dangerous situation in big waves is to be in the wrong place when the wave breaks. As I understand it, the reason that the Pardeys prefer to attach their para anchor to the forward quarter and thus have the boat lying at an angle to the waves is that by lying at that angle the boat creates a "slick" as it drifts slowly downwind and this slick prevents the wave from breaking at that point. As a point of detail, I think they attach the para anchor to the bow but then run the warp through a snatch block which is attached further aft and thus make an adjustable yoke.

 

[vyv_cox]

Yes, I'm familiar with their suggestions, although I think it's the parachute that creates the slick. The length of the warp needs to be tuned to be about one wavelength to to put the parachute in the right place to achieve this.

On my boat I have no idea where I could attach the secondary warp so that it would be secure. I have spring cleats half way but these are attached with 4 x 6 mm bolts, via either an aluminium tapped plate or penny washers and nuts. In neither case would I like to hang half of the force of the lateral projected area of the boat on them. Maybe the genoa sheet cars but the angle would be far from fair. Chainplates doesn't seem like a good idea. I have a few U-bolts but again, these are not all that substantial.

Also, the main warp would pass either through two fairleads, attached with two 6 mm bolts tapped into stainless steel plate, or through the bow roller, very substantial but subject to considerable chafe if the warp was at an angle of ? 30 degrees. I carry lots of lengths of plastic tubing for use as chafe reducers but I don't fancy their chances in these conditions, and I would not be the first to volunteer to go forward to check them!

After lots of thought, if it ever comes to it I shall probably hang off the bow. Most of the examples given in the website seem to have done that.

 

[ccscott49]

I do have fairleads which I could use, aft from the bow, but I agree with you about the bow roller, over 30 deg and I would also be up against the side pieces and I think my plastic pipe would last about 1/2 hour under those conditions, so if I were have a para I would have it directly over the bow and as you say spaced so as to put it on the back of one wave away or possibly two, if they are close together. But I don't have one right now and I think I would consider on of those multi para thingies, with lots of smaller paras on a long warp, I've heard a lot of good things about those and the fact they are considerably easier to recover.