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Nomad revisited

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After dawdling around a bit it’s become obvious that I really miss having a trailerable proa at hand. At the same time the idea of building another 14’ “trial horse” doesn’t have much appeal, I’m beginning to suspect that there is going to be a limit on the number of boats left in this writers bucket list. So rather than build a trial horse boat that will rarely if ever get used I’m considering jumping off the deep end and build a replacement for P52. Hence this topic to get some feedback on what I’m planning.

Basically Nomad (~ 16 sheets 6mm plywood) is just about halfway between Gary Dierkings simple elegant Wa’apa (5 sheets 6mm ply) and John Harris’s Madness(35 sheets). The two most obvious deviations from the original design brief are rig and rudders.

Rig is a bidirectional cambered junk. Switch of tack position on shunts is along a piece of 1” pvc pipe along the lee gunnel with a shuttle fabricated from a piece of 2” sch 80 alum pipe and UHMW bushings. The matching shuttle on the boom also slides on a piece of 1” pvc pipe. Not shown on the attached renderings is the typical web of mainsheet lines along both ends of sail. Mainsheets are run thru blocks on the float and the forward set function as parrels. It’s also possible to vary the location of the boom in relation to the shunt shuttle for balanced downwind running.

Rudders…....The bearing surface is a tapered cone, model doesn’t quite have it right but I’m tired of fiddling with sketchup. Still the geometry works, rudder assemblies are held in place with bungied spectra lines that run thru hull with sheaves at each side. Steering cables run along edge of cockpit windward to leeward, initial thought is to have pull to windward with turn boat to windward, opposite of what a tiller would do (hand steering by cable was fairly easy to adapt to on sailing canoe). Construction is currently envisioned as hotwired chunk of foam in the hull, finish sanded, glassed and graphited on bearing surface. Rudder assembly is probably a plywood trunk with shaped and glassed foam side cheeks. Also a replaceable UHMW shaped shoe at the base of the assembly.

Another area I’d like some feedback on is I’m considering making all the long pieces particularly birdmouthed mast from strips cut from a 24’ piece of LVL beam.

Take a look and let me know what you think, this is my first round of curvilinear work with sketchup. The overall configuration and dimensions are quite close, float is a little too full (elliptical rather than Speer section) hull a little too lean (circular arcs rather than quadratic parabolas).

Almost forgot, unless someone can make a convincing argument otherwise, Nomad is going to start out life leeboardless, balancing the simplicity of not having one with the hassle of cutting into the float to install a trunk if it turns out to be necessary.

cheers,
Skip

 

      [ Edited: 29 August 2012 10:02 PM by Skip ]

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Additional pics

     

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Love it.

Can’t wait to see the details of the sheeting/parrels.

I would think you have plenty of lateral area in that foil.  any worries about it giving a lot of weather helm, or do you think the rig CE and extreme aft placement of the rudder is going to balance that?

Tom

     

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I don’t think there will be any problems with weather helm, P52 with a very similar configuration did fine once rudders were installed. Certain situations with with steering oars in higher winds could be challenging.

The tack of the sail can be moved a foot or two fore and aft if needed, hope that won’t be necessary, futzes with the ease of shunting.

Tweaking the sketchup model for running configuration showed me some difficulties with the geometry of the sheet/parrel arrangement that I hadn’t anticipated. Looks like a real physical model is in order to work out some details before going full size. Really needed to be done anyway to check out where boat ended up if blown over on it’s side.

cheers,
Skip

     

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When looking at this type of sail, I considered parrels that “widened” at each batten so the ends served as stops for a pair of down hauls.  The fun part was considering what the boat would do in the brief moment the sail was broadside to the wind in a traditional shunt.  When Bolger did his version, he showed heading up into the wind, then reversing the sail to head back downwind for starters as an alternate shunting method.

with the parrel idea above, I figured that when one was sitting with the wind coming over the AMA and the sail weathervaning, the down hauls could the be swapped and the new balance would weathervane the sail around without ever being broadside to the wind with tight sheets.

Like I said, I’m REAL interested in your solution grin

Tom

     

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Nice job with SketchUp, the most boat unfriendly 3D modeler ever devised, and yet… strangely addicting.

So rather than build a trial horse boat that will rarely if ever get used I’m considering jumping off the deep end and build a replacement for P52.

“Danger, Will Robinson. Danger!” The “trial horse” aspect is what we need when traversing uncharted design waters. If you don’t have the patience for a 16’ test, than promise us you’ll build a sailing model. grin

You have a consistent interest in the buoyant foil ama, or “floil” as the AYRS would say. As apposed to a more “normal” log or hull shaped ama with a daggerboard. I’d like to hear your reasons for that sometime. The reason I ask is because Bernard Smith used buoyant foils in his sailing models for Little Merrimack with great success, however was disappointed at full size, something about Froude numbers or problems of scaling, as I recall.

As Tom said, I’ll be very interested to see your solution for the sheets/parrels. It’s a square rigger turned sideways!

     

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Thanks for the compliment, SketchUp is new to me, I had pretty much retired from 3D computer graphics a long time ago but a client twisted my arm a bit and SketchUp was the easiest way to get the job done. I can hear rubyscripts calling in the distance “just one more time, we’re easier, better than AutoLisp” but don’t think I’ll travel down that road. Too many boats left in the queue.

There is danger in those uncharted waters but I’m of a mind to charge ahead. The problem with the 14’ (not 16’) “trial horse” is that it’s a boat I’d not ever use after a short development cycle and there would still be stuff that would need to be worked out in the larger camp/cruiser. Sailing models are a mixed blessing, one of the major issues you touch on in that Bernard Smith had troubles going from models to full size. Still I may do the model to sort out rigging issues and what happens when the boat goes over on its side.

There’s no doubt I’m fixated on bidirectional rigs and floils, not sure that rational reasoning is involved, but since you asked. Part of the reasoning is I’m just way off to one side of the bell curve. The first Texas 200 I participated in, the first nights camp was at Hap’s Cut, far from normal civilization with a far from normal group. Part of the discussion under the only shade tree for many miles was “why such a strange boat, isn’t it enough to just be doing this oddball thing?”. There’s no really good answer, it’s just “it is what it is”. The proa fixation started with a $50 sailboat race and the idea that the “best” sailboat you could build from a particular pile of materials was a proa insinuated itself in my psyche and hasn’t left (it really is true wink ). Bidirectional rig obsession is a mixed blessing, after several attempts at bidirectional rigs and crab claws I’m of the opinion that bidirectional rigs are best suited to a bidirectional boat but that more investigation is in order.

Back to floils and your original question. Part of the obsession is finding the elegant simple solution to whatever the problem. Floils are one of those things that has the potential to do two things well at the same time, AND do it in less than knee deep water, a real consideration here on the Gulf Coast.

I’ll probably build a model (non sailing) to sort out some of the rigging/shunting issues and YouTube it. Am going to visit this afternoon with a like mind aka John Wright and we’ll see what develops, great fun.

cheers,
Skip

     
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Hi Skip,
as I saw your steering system I remembered something similar in my archive. And here is it. It was the 20 ft. proa KIA KIA from Chris Hughes, think it was built about 10-15 years ago. Sorrily I have no address so we can’t ask him about his experiences.

 

     

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Thanks much, I had read about KIA KIA some time ago but had not seen the photo.
So my rudder system is going to be a blend of Chris Hughes and others (Newick, Brown, Stevens….). I admire them all.

Thanks again,
Skip

     
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I’m a little worried about the sail being briefly under full power during the shunt.  Under extreme conditions, this could be big trouble.

     

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Gary_Dierking - 31 August 2012 01:17 PM

I’m a little worried about the sail being briefly under full power during the shunt.  Under extreme conditions, this could be big trouble.

Thanks, this one gave me pause to think.

On the one hand in my limited experience the only white knuckle moments I’ve had weren’t shunt related but rather times the tack came loose and there was a lot of stuff blowing around attached only to the masthead. Once with crab claw other two two were with shunting staysails, crab claw was gear failure, staysail events were more directly due to operator malfunction.

On the other hand in extreme conditions or as close as I’ve been there’s always been other problems/failures before I had a chance to experience shunt trouble.

After thinking about the the deal a little more it makes sense to do the 14 footer first and wring it out a bit, I’m still not convinced that model trials translate that well to larger scale. Not that I’ve got anything against models, I built a bunch back when RC equipment had tubes (and later).

For me shunts are normally done headed up into the wind and there is a brief moment when the tack is slid to the other end of sail that the boat can accelerate briskly headed into the opposite tack but it’s always seemed a nominal event. More trials are in order so it’s back to a Bionic Broomstick and a round of test as soon as I get the time.

cheers,
Skip.

      [ Edited: 03 September 2012 09:46 AM by Skip ]
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Gary_Dierking - 31 August 2012 01:17 PM

I’m a little worried about the sail being briefly under full power during the shunt.  Under extreme conditions, this could be big trouble.

I wouldn’t worry too much about the momentary “broadside” condition, for a couple of reasons.  Firstly, the sail is not at all “under full power” during the shunt, but is in fact quite depowered as the flow of air across it has stalled out so the aerodynamic effects are negligible and the only forces at play are strictly of the laundry-hanging-on-the-line sort…  Secondly, so long as the two tacks/clews are being held taut everything remains quite docile in much the same way as an old-school symmetrical spinnaker remains tame with both port and starboard guys hardened through a gybe.  Granted, the gybing maneuver eases loads even further by maintaining some degree of boatspeed to lower the apparent wind, but I don’t think it would be overly onerous without it either.

     
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Great ideas, well presented.  My thoughts-

Shunting: 
If you let both ends go, the whole thing will flap, and give a lot of resistance and shake like crazy, agreed - not so good.

The sail will have less force in it once stalled - consider how the speed picks up dramatically from a dead run to a reach.  So shunting should be a piece of cake -  harden in (rear) sheet.  Sail stalls.  Bear off.  Let off new rear sheet. Off you go.  Sounds easier than swinging a conventional sail through 150deg.  Only problem I see is that if when you sheet in and stall, will the boat want to head to wind, making bearing away dificult. I have a feeling it will do the opposite, any comments?

love the junk sail. Great if the conditions are looking a bit dodgy, dropping a panel or two, or the whole sail, is dead simple.  Junk rigs have been tested with the centre of pressure at various points.  50% as you have lost very little to the more normal of around 30%.  Only downside with a double ended sail, is that it has to have thin leading edges.

Is that an end plate on the ama?  Very intersting, it would help with resistance, but would give a sudden release as it comes out of the water, so not so good.  Better on the main hull.

Regards
Mark

     
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Mark - 03 September 2012 08:49 AM

Great ideas, well presented.  My thoughts-

Is that an end plate on the ama?  Very intersting, it would help with resistance, but would give a sudden release as it comes out of the water, so not so good.  Better on the main hull.

Regards
Mark

Yes it’s an end plate and a skid plate and a step for old guys to climb back in the boat. Will probably be a piece of recycled UHMW shape to be determined by trial and error. Skid plate function fairly important in my area. Step is non- negotiable in one sense, it will be there so I can negotiate getting back in the boat.

My interest is in quick easy cruising, a racer I’m not, I think that cruising proas are happiest with float in the water, very little at times but still…... The sudden release and slide downwind is a safety feature to me.

cheers,
Skip

     
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Mark - 03 September 2012 08:49 AM

Great ideas, well presented.  My thoughts-

Shunting: 
If you let both ends go, the whole thing will flap, and give a lot of resistance and shake like crazy, agreed - not so good.

Regards
Mark

Having had both ends “let go” a couple of times, you are right, it’s not something to take lightly.

Hence Nomads rig will have one permanent tack that slides from one end to the other.

cheers,
Skip

     
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John Dalziel (owner of the Yahoo proa_file group) built one of the Bolger proa rigs more than ten years ago and the shunting scared him enough to give up on it.  You might want to contact him to retell the story.

     

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