Design and Use of Drogues

  • 18 Mar 2018 19:17
    Reply # 5985167 on 5984586
    David Tyler wrote:

    Likewise, it should not be beyond the wit of man to devise a chafe-proof leader, drogue and weight arrangement. So long as there is the will to put the necessary quality of materials and workmanship into the project, that is.

    This seems like the perfect opportunity to borrow a bit more of the collective wit here.  Users of the Jordan Series Drogue often have dedicated "chain plates" bolted to the to the port and starboard quarter to attach the drogue.  This, used with a bridle, seems like a very strong arrangement and a great way to avoid chafe through chocks and around cleats.  I welded reinforced tabs in place for this purpose while refitting Leeway.  However, you can't adjust the length of the rode if you do this.  So, how do you create a chafe-proof lead that also allows you to adjust the length of the rode?  The only solution I've come up with so far involves my aft cleats and chocks, the lead is good, but even with chafe gear I suspect I would have to regularly let out a bit more line to combat chafe.
  • 18 Mar 2018 08:08
    Reply # 5984586 on 833331

    I feel absolutely certain that had Oscar Wilde been an offshore sailor (not beyond the bounds of possibility - Hillaire Belloc was, after all), one of his memorable bons mots would have been:

    "To be caught out in one survival storm may be regarded as a misfortune; to be caught out in a second survival storm looks like carelessness".

    If the drag device acts like the airbag of a modern car, and saves my skin just the once, I can forgive it for not being in a fit state for a second survival storm. I could not, however, forgive it for failing to remain in a fit state to be deployed on a discretionary basis during routine gales. That's not too big an ask. It should be evident that if the bridle of a drogue is lead through fairleads to cleats, there is a strong risk of chafe. It should be shackled directly to two strong fittings on the quarters. Likewise, it should not be beyond the wit of man to devise a chafe-proof leader, drogue and weight arrangement. So long as there is the will to put the necessary quality of materials and workmanship into the project, that is.

    Last modified: 18 Mar 2018 10:10 | Anonymous member
  • 18 Mar 2018 00:22
    Reply # 5984343 on 833331
    I suspect that most drag devices will work adequately well, with most boats, in certain conditions.  While it's important to find a 'one size fits all', if such a thing exists, I think the emphasis must be on its being fit for purpose, which is to say that the device has to survive being out there for more then one storm, before needing to be repaired or replaced.

    Fifty years ago, Voss's sea anchor was all the rage, but they invariably shredded if used in earnest for many hours.  With modern materials, they could probably be made to last a lot longer, but at the end of the day it is chafe that is the big issue: chafe where the ropes come on board, chafe of the gear in the water.  So far, none of the existing devices seems successfully to have solved this problem.  For this reason, it may still worth carrying several long lengths of rope and a tyre, so that when the second storm comes along you have something else to deploy!

    But keep up the good work, innovators all :-)

  • 17 Mar 2018 17:27
    Reply # 5983995 on 5982090
    David Tyler wrote:You may have a point there, as the Galerider drogue, constructed as a webbing lattice, works by creating a lot of turbulence as the water passes through. I made my own version of this, and tested it (only once, in a fresh breeze, when I wanted to slow down for a dawn arrival, not in a gale or storm). It worked as I would wish a drogue to work, with minimal drag at very low speeds (useful for recovery) but effectively putting on the brakes at 4 knots.  

    I've ordered a metre of heavy duty mesh fabric - enough to make four 30cm, or two 38cm, or one 38cm + two 30cm cones. Nothing can be learned without conducting practical sea trials, and I don't see why Arne should keep to himself all the fun of doing that!

    I agree, the mesh should cause the drag to vary more with speed.  I also think it has a stabilising effect hydrodynamically in that it helps spoil lift an outer surface might try and create as it starts to yaw.  I suspect a more open weave fabric like used on sun shades and lawn furniture would still provide adequate drag as speed increased, although I don't know if it would be adequately durable.  
    Last modified: 17 Mar 2018 17:28 | Anonymous member
  • 16 Mar 2018 14:09
    Reply # 5982109 on 5978881
    David Tyler wrote:

     In fact, a scoop, plough or claw anchor would have something of a paravane effect, drawing the drogue deeper, as well as stabilising it against yaw and rotation, so this ought to be the necessary weight, IMHO.

    One caveat to that! One instance where the use of a drogue has been a lifesaver is in maintaining directional control when crossing a river bar against the ebb in a gale, and it could (would) be disastrous if the anchor touches bottom.
  • 16 Mar 2018 14:04
    Reply # 5982090 on 5978576
    Darren Bos wrote:

     My limited experience makes me think that the larger cones seem to behave worse than smaller ones.  

    I think maybe it's the case that it's the length of the cone that matters most, with  longer cones being more stable than shorter cones and parachutes.

    So, although the JSD cones seem smaller than necessary, I wouldn't want to go with too small a number of larger cones.  Making the cones out of a mesh might improve their behaviour without a large decrease in drag. 

    You may have a point there, as the Galerider drogue, constructed as a webbing lattice, works by creating a lot of turbulence as the water passes through. I made my own version of this, and tested it (only once, in a fresh breeze, when I wanted to slow down for a dawn arrival, not in a gale or storm). It worked as I would wish a drogue to work, with minimal drag at very low speeds (useful for recovery) but effectively putting on the brakes at 4 knots.  

    I've ordered a metre of heavy duty mesh fabric - enough to make four 30cm, or two 38cm, or one 38cm + two 30cm cones. Nothing can be learned without conducting practical sea trials, and I don't see why Arne should keep to himself all the fun of doing that!

  • 16 Mar 2018 13:43
    Reply # 5982036 on 833331

    I note that Englishseadog on eBay.co.uk. is offering ten JSD cones, ready made to a high spec, for £30 - good value:

    "The specification and construction of these cones match or exceed Don Jordan's and the US Coast Guard specification.

    The cones are made of a 7.2 ounce yellow polyester (Dacron), with 3 x 12mm tapes sewn to the outside. These are the toughest cones on the market !!

    They have have a 5" mouth and 1.5" exit. The mouth and exit are reinforced with tape sewn all around."

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  • 16 Mar 2018 10:56
    Reply # 5981855 on 5957651
    Annie Hill wrote:
    Jim Creighton wrote:
    Could you expand on this a bit for us? How was the boat steered in heavy wind? By hand mostly or self steering?
    With the exception of one occasion, where we had a something break on the self-steering gear (I can't remember what it was) Badger always ran before a gale steered by the windvane - unless, of course, we were close to shore.  Sometimes we would let the lowered mainsail out, sometimes it was sheeted in, depending on the conditions.  It was quite wonderful to stand in the pramhood and watch the waves thunder down towards her and then see how she would rise up their faces with only perhaps a bit of foam from the crest spilling over the stern, while the self-steering gear kept her on course.

    Thanks Annie, Very reassuring.
  • 15 Mar 2018 01:02
    Reply # 5979390 on 5978034
    David Tyler wrote:
    Graham Cox wrote:
    David, how many of Jimmy Green's 30cm drogues do you think would be needed in series to have the same effect as a JSD for a 6 tonne boat?
    Without any hard science or experience to go by, I'd have to compare frontal areas. For this size of boat, the JSD recommendation is for 107 cones of 5in diameter, and I calculate the total frontal area to be 13554 sq cm, or 2100 sq in. (the Para sea anchor size would be 9ft diameter, which is about twice that area). That would be the equivalent of 18 x 30cm cones, or preferably (since smaller cones take just as much labour to make as larger cones, since I get bored when I have make more than a dozen of anything, and since the main aim is to spread a number of cones out along a long line) 11 x 38cm cones on a 55 metre line, with a 25 metre leader.

    Very good science, David.  Thanks for that.  I already have a 107 cone JSD but don't trust the cones' lightweight construction.  I wouldn't throw it away, but if I built a backup or replacement, this is the way I will go.
  • 14 Mar 2018 19:49
    Reply # 5978923 on 833331

    I think the reason for the modest weight is to aid in retrieval, but agree it was on the light side.  It would seem that a flatwater test would be a good start for any drogue device, first observing it about 40' behind the boat while to boat is trying to do its maximum speed (even this won't replicate the boat trying to surf down a wave).  The benefit of chain is that it won't twist the rode, unfortunately it is a pain to retrieve by hand.  I'd experiment towing any anchor at high speed before choosing it for a weight, I think a lot of anchor designs would spin at speed.  The Fiorinteno Shark uses a 30 pound mushroom anchor which might be a reasonable compromise

    Yes, the deployment looked sloppy.  Part of the marketing of the Shark drogue is that it is easy to throw and deploy.  I suspect the sloppy launching was not-so-subtle marketing.  However, it is also true that once a drogue catches in the water you have little hope of controlling it.  Years ago, I used pancake bags to flake climbing ropes into.  Even after transport, the lines would feed  without mishap.  It seems like all drogues should come with something like that.

    With any drogue, it seems like part of the sea trials should involve trying to recover it while the boat is moving (motoring), to simulate when you want to get going again after the storm has passed.  This seems to be the weakness of the JSD.

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