Subject: Re: safely using Drogues and Para Anchors
From: Mike Crawford
Date: 2/21/2006, 7:21 PM
To: rob dalton

<<I appreciate your damping of the almost acrimonious debate. I am after reasoned engineering for criticism so I can learn and tend to get impatient with liturgy.>>

  No problem.  Sometimes I think I'm being too wishy-washy, but I give it a shot anyway.

  I don't blame you for getting impatient.  I'm disappointed in the lack of thought some gave to the Jordan site, particularly the report.  I'm all for criticizing ideas after one has attempted to understand them, but a number of folks clearly didn't bother to think or read before posting.

  Sometimes, as with the rig discussions, I'm amazed at how tightly people cling to their preconceived notions, not even absorbing the other sides to the discussion.  And this is supposed to be a forum about an innovative boat that breaks the rules of status quo.  Odd.

---

  i agree with you on the drogue system.  Redundant, mechanisms, ease of deployment (just pay it out), better continuous loading, lower maximum loading, quicker response to breaking waves, less likely to foul.  They make it hard to argue for a single large para anchor.  I've never set one myself, but I've read many stories about people who have botched their deployment during really bad weather.

  The only thing I question is the ability to adjust the loading by varying the amount of the drogue line paid out.  Everything I see on the Jordan site shows a fixed bridle going out to lines that then attach to the drogues.

---

  Your repeated posts over time are slowly infecting me with the wharram rig.  My ideal rig would be a reef-able dynarig, but the dynarig folks are hard to find these days, and I'm not sure if they ever solved the reefing problem. 

  While I'd hate to give up my pretty golden mylar Pentex sails, I'll admit that this is somewhat of a shallow desire.  With the strengths of the wharram rig, it's possible that the stiffness and high modulus of Pentex aren't important.  The additional area aloft, and the shaping from the gaff, combined with the smooth leading edge, could make up for the soft sailcloth.

  I wish it were possible to test a wharram rig versus an equivalent una rig, and then look at the costs.

  I'll post the wharram thing sometime in the next few months (after the trailerable issue).  I just want to wait until I'm quiet for a little while, and also until I've finished reading all the past postings.  I'm slowly getting there.


       - Mike



rob dalton wrote:
I started to realise what I had been doing after an  excessive number of memorial services and that three of the boats I had worked on were on the bottom. It started m ehtinking seriously about safety at sea from an engineering perspective.
 
To me the series system with continuous loading along the line should give better surge characteristics , be less susceptible to wrapping itself round bits and pieces- as happenned to that bloke trying to kite his way across an ocean, failure of an element is not catastrophic, easier to launch
 
I think I have come to the conclusion that most modern sailing boats should be attached at the bow if current is their main concern and by the stern if wind is the problem. For a Harry this is not a problem. The long, low rocker hulls means that the boats will respond to the pressure on the bow from the rode, due to oscillating winds, with a damped motion.
 
I appreciate your damping of the almost acrimonious debate. I am after reasoned engineering for criticism so I can learn and tend to get impatient with liturgy.
regards,
Robert

Mike Crawford <jmichael@gwi.net> wrote:
<<I have been one of those fishermen who have fished in the Tasman sea for a living>>

  Well then, my hat is off to you.  :-)

  I also really like the theory of paying out more or less of the drogue line depending upon how much you want to slow your progress.


       - Mike



Robert wrote:
What I like about the combination of a Harry and a jordan series
drogue is that if you want to slow the boat to almost a stop, ie a
para anchor, then you merely pay out more elements to you get to the
same total area of the equivalent para chute anchor.

There has been derision about anchoring from the stern without a
solid explanation why. On some boats it is quite successful and much
more comfortable in that it reduces yawing.
(I have been one of those fishermen who have fished in the Tasman sea
for a living)
Regards,
Robert


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