Subject: Re: gunters, wharrams,
From: Mike Crawford
Date: 2/22/2006, 9:36 AM
To: rob dalton


  The gunter rig could work, but I'm hesitant to use a second spar that carries a load.  The Wharram spar doesn't do a whole lot other than support the sail and keep its shape, so that doesn't disturb me as much.  A gunter, or anything with a sleeve, creates a joint that will have to bear a lot of dynamic loading, and I'm not the type to be a test platform for something that could fail in a bad way.  Forgetting safety and sailing issues, I'd just be worried about tearing a sail that size.  Those things aren't cheap.  With a gunter, that joint would also have to move up and down the mast as the sail is reefed, and that's another worry.  That would have to be a pretty strong car.  Heck, i worry about that with the Wharram spar, and it's not really loaded.

  I hadn't thought about the problems with the sleeves on the Wharram during a capsize.  Now that you mention it, though, I can remember Rob talking about how hard it is to right the Elementarry once the sleeves fill up.  It makes sense -- Wharram designs his boats with a lot less sail area in order to be safe for cruising, and since they're not likely to right if they do go over, water in the sleeves reallyisn't an issue.  It is an issue if you're going to push a harryproa to its limits, though.  You'd need a line to winch the sails down before righting the boat.

  While it's probably not really feasible, I like your bladder idea a lot.  Could you imagine the great wing shape and massive flotation that would provide?  Of course you can, but I have to ask the rhetorical question anyway.  The biggest problem would be dealing with it in sections in order to handle reefing.

  Or, since the mast rotates, the mast itself could fill much of that sock.  You could build the masts as they are, to handle the loads, and add big fairings to leeward, to fill out the wing and fill the sail sock.  You wouldn't need much structure at all for that wing section, and since it's the front of the mast that takes most of the load, there's no need to beef up the wing to handle a track.

  However, you'd still need a fair amount of slack in the sock in order to allow the sail to bunch up for reefing.  Or, the bottom of the mast can just be circular, leaving lots of space for reefing, with the wing starting a few feet higher.

  I don't think I'd be interested in a Wharram without the sock.  Adding a track just adds expense, complexity, and points of failure, while giving up the clean leading surface.  Once that happens, I'm more likely to go with a battened una.

  I do envy the ease of use of a single una or easyrig, but I'm also hesitant to give up on the schooner for the reasons we discussed earlier: the extra sail area it can carry in light wind, the lower center of effort, the simplicity of having only one type of sail on board, the superior steering if the rudders go, and so forth.

  What a great design challenge this is!  You're right:  there's no telling what will happen with these boats over the next few years.  Rob is really innovative, and a lot of people are helping to push and/or pull him in new directions.


       - Mike




Rob dalton wrote:
Must admit I glossed over that section as something to be sorted out when building. I figured I'd just glass on a loop of uni or kevlar. I plan to have a few loops around the boat for attaching things like fenders or bases of bipods for lifting things.
 
You could get the extra height with a gunter rig for an easy rig on a sleeve that can travel to just below the jib stay.
 
The taper on a mast for a wharram configuration would probably be a bit less so it shouldn't be an issue providing the sail is cut accordingly and you'd have to rig up an outhaul on the gaff. Abrasion resistance could probably be overcome with a light kevlar layer. 
Rob reckons they are a hassle if they fill up with water when they fall over. I was wondering if the sock could have a bladdere run the lenght of the sock which can be inflated for improving both bouyancy and shape but deflated in  hurry when you want to bring it down. Almost certainly more trouble than it's worth but I couldn't resist the idea.
 I can't see any reason not to run the sails on a track with the gaff on a small car. As the sails can be weather cocked on any point of sail, there isn't  extra advantage in easy downhaul downwind.
 
Who knows what morphing will be done in the next few years. It is pretty staggering how far it's come since the first Harry
regards,
Robert

Mike Crawford <jmichael@gwi.net> wrote:

  Did you read what Jordan wrote about the bridle going through chocks and then to a cleat or winch?  I was wondering about the loading myself, but just figured that I'd put in a large backing plate.  He actually suggests straps on the hull, connected to thimble ends of a bridle using shackles.  Not much chafe in that solution, plus it's probably more likely to survive a huge load.

  I'm also not fully set on rigs.  However, despite my appreciation for the easyrig's ease of use, I'm still predisposed against it because of the 64' height limitation for bridges.  I don't think that I can get the light wind performance I want with a mast of that height.

  I love the schooner for all the reasons we've discussed, but then there's that extra weight and cost.  I like the una rigs, but that wharram looks darn efficient, and also inexpensive (comparatively speaking, of course).  My one big question about it is how to anchor that gaff to a mast with a changing diameter, and do so without chafing the carbon/epoxy, which I'm told does not have high abrasion resistance.

  I'm glad that my boat is at least a few years away.  Not only does this provide more time for Rob, Mark, and the folks on the forum to come up with improvements, it also gives me time to figure out what the heck it is that I want to do.  That's probably the toughest thing.  In many ways it's easier to get a production boat and accept its limitations.  Having complete freedom requires a lot more thought and weighing of options.

       - Mike



rob dalton wrote:
This is a hassle, The line needs to be retrieved , retied witha rolling hitch and let out again. A pair of bridles could make it more comfortable. Tie the one not under tension  then haul in the other untie and let out the extra. You'd get pretty fast at tieing a rolling hitch.
 
I'd also like to see a comparison between a Wharram rig and a una. My plan so far is to use a schooner wharram type rig with a better shaped gaff. This is a long way off and I'm starting to see some of the advantages of the Easy rig in terms of bow loading.

Mike Crawford <jmichael@gwi.net> wrote:

  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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