Ultimate 18' Tri ?

I wrote a while back about a tri using an ama that rotated about it's longitudinal axis. The ama would have a shape such that one half the ama was a displacement hull with a length to beam ratio of 18-20/1 ;the other half was a stepped planing hull similar to Parlier's cat.
Rotatable Hull(ROH) Multifoiler - Boat Design Forums
Address:http://www.boatdesign.net/forums/showthread.php?t=10267&highlight=ROH Trimaran
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My latest thoughts on this are to make the foils on the main hull fairly small and not to use them to lift the boat before ama rotation. As the boat begins to plane on the rotated stepped ama's the loading on the foils would be very low since their entire mission would now be pitch control only-not used specifically for early lift and not used to add RM.
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PS- the new stepped amas on Hydroptere are a shorter stockier version of what I have in mind-they do not rotate but their shape ROUGHLY illustrates the similar shape of the model I used to test this geometry.
All I need now is for someone to put up the 100 grand(more or less) to have Eric Sponberg engineer this thing and to build it.
I think this concept offers very high potential speed and sitting here looking at the remnants of Barry pass by sparked my thinking along these lines again...
This should bring you to a close up of the stepped ama's on Hydroptere.
Hydroptere
Address:http://www.hydroptere.com/index.php4?lang=EN
Now visualize this ama upside down and that would be the sub-planing attitude of my hull. Right side up when planing.

 

This is always going to be too expensive!

Hi Doug, You are right into my "territory" suggesting an 18ft. killer tri.
However I think that 100 grand might be the finishing price for subsequent boats, with the development of the prototype quite a bit higher.
Even if you had a sponsor with unlimited funds, which is so unlikely to ever happen as you would need a pure altruist. The market for such a machine I see as nil; even you could not come up with a convincing argument as to where paying clients would come from. The vaka with lifting foils could easily be a Moth foiler scaled up around 65% in all dimensions. This would give you a vaka of around 18ft. 2inch in length and max. beam of 20 inches. Is it going to be a single or doublehander?
Now you want a square configuration so lets say a beam of 18 ft. I guess the least expensive option here would be to purchase 100% carbon/epoxy tubing from a high tech specialist tube builder such CST composites. Even the building of the amas with a displacement shape such as that on a Hobie Tiger on one side, and then like Parlier's Hydraplaneur on the 180 degree opposite side, would not be insurmountable either, but definitely not easy. L/B ratios of the two configurations would probably need to differ for max efficiency. The displacement side obviously needing much more fineness generally, and forward sections with a wave piercing characteristic shape. Planing is far more efficient and earlier with lower L/B ratio, and very little fineness in hull shape after about 30% of the way behind the bow.
In my opinion we have now done the easy stuff, and the rest becomes incredibly challenging in an engineering sense.
I would guess that you would want a little more sail power than that provided for by a Hobie Tiger, as overall beam is huge and overall weight almost certainly higher than the Tiger. It will need to be a stayed rig in my opinion, but I could be wrong. If stayed, then it would definitely end up quite a bit lighter overall.
Staying points would be a little inboard of the outer ends of the crossbeam, to avoid impinging on the complex mechanism required to mount the crossbeam tube to the support that needs to rotate. What if the configuration of the mast step and crossbeam position do not correspond to a a sensible sweep back angle for the side stays? I can't begin to see how you could mount a chainplate on the rotating ama. On my amas the chainplates are mounted on the amas, exactly midway between the locations where the front and rear crossbeams intersect with the ama.
Possibly the unstayed option might be better, even with the weight penalty. Even so I can see that that the huge lateral forces on an unstayed mast on such a powerful 18 footer would probably disintegrate the hull around the position where the mast penetrates the vaka, when the breeze comes up.
What mechanism would be employed to rotate the amas 180 degrees? Maybe an electric motor? Weight, plus more weight for batteries. This will then need even more sail power than initial estimates. You then have to consider longitudinal stablity very carefully as a catastrophic pitchpole over the bows is starting to become quite a likely consequence in a decent breeze. Don't even go there, saying that this would be a single hander, and the rotation would be manual, requiring human muscle power.
What about the engineering behind the complex joints between amas and crossbeams. I have some doubts that even Eric Sponberg will be able to solve this one, in such a way that it would be capable of thousands of rotations on open water while the tri is moving, without breaking up. Don't bother with the entire project if the skipper has to decide before launching which configuration, displacement or planing, for the amas is the correct choice.
Honestly, even for you, I think that you have aimed far too high this time!

 

Ultimate 18?

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Why, thanks Frosh, I do my best. And thanks for your reply.
1)The rotation is only done at the as yet to be determined crossover point-not necessarily when the main hull flys(which will be at about 6-8knots boat speed max.) but when the planing hulls will work optimally.
2) Rotation will be manual and very simple and quick-it would not be frequently done at most venues.
3) Shrouds ,if any, will go outboard almost max(or where Eric says). I would like to look very carefuly at an unstayed highspeed rig like a Moth type(w/o the stays) as well as a wing rig for a speed version depending on weight. My realistic guestimate is that a partially stayed rig will be required.
4) Estimated upwind SA for this boat is 380sq.ft. compared to 227 for the Hobie Tiger. The Max RM for the 18 tri would be 10512 ft.lb vs 5197 ft.lb for the tiger-over TWICE the Hobie RM for the 18.
This is based on two crew of 160lb. each on trapezes with the 18 just flying the main hull and the cat just flying the windward hull.
5) The 18 would have 2lb/sq.ft. sail loading vs 3.15 for the Tiger.
6) The Hobie weighs 397 lb. and is fiberglass/foam sandwich and this boat would be 100% carbon foam/honeycomb and a very rough estimate of weight would be all up at 447lb.
7) Eric Sponberg is one of the premier naval archtects and marine engineers in the world today and he would do an exemplary job on this boat.
8)The boat could be "toned down" substantially and still beat most beach cats. The idea here is to illustrate what is possible with the trimaran configuration. One of the central themes of the 18 are the small hydrofoils on the daggerboard and rudder-FOR PITCH CONTROL ONLY. This,and the fact that the center of buoyancy moves forward when the ama's are planing will give the boat extraordinary resistance to pitchpoling.

 

What Now?

Hey, it's your money...

Funny part of all this is, you could get beach cat killer performance out of an 18' tri by simply building the boat light and strong, not using any failure prone rotating anythings and sailing it well. None of the trick stuff is necessary. Just simply done, well-proven parts and design layouts that are executed nicely.

The Nitro trimaran out of France, http://www.navaldesigner.com/en/index.html (in the Gallery section)
has already done all the, flying the main hull, stuff from a compact design of 4.6 meters LOA and it used no trick anything in the way of rotating parts. If the builder would simply install a bigger rig, spread the beam just a bit and put her back in the water, you'd have the tri that could kill any beach cat under 20' that is out there. So, you are blazing what new trail here with this overly-complicated design idea?

What is it that makes people think they are advancing the craft when they toss yet more complicated mechanisms into the mix? How about something like a thought-through design concept that actually simplifies the whole potential of a given design idiom so that more people can enjoy the potential rather than a self-limiting smaller number due to complexity?

Chris

 

Ultimate 18?

Actualy, the ROH system is quite simple and robust and with a potential of 40+% less drag at planing speeds offers quite high top end speed-much higher than available thru a "normal" displacement hull multihull. And with none of the low and medium speed problems associated with Parliers cat. The combination of planing ama's and the use of relatively lightly loaded foils for pitch control offers unmatched pitch stability for a multihull of this size.
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Thanks for the Nitro-looks good. But I can't find any specs anywhere.....

 

Language gymnastics.

Hi Doug, you might think that you have some talent with misuse and twisting of the English language to suit your purposes.

Originally Posted by frosh
Honestly, even for you, I think that you have aimed far too high this time!
Well thanks Frosh---- QUOTE- Doug Lord.

I think that you have been well and truly trumped.
Go check out your/mine latest posting re Chris Oslind's latest S & G tri in the Design section. Happy reading!

 

Jeez- Doug, I expected a massive response by now. What has happened to the big man with so much to say?

 

18' tri's

I've gotten into doing more research on small tris in the size range of the previous post. I think I know most of the existing designs and concepts but in case I don't: is anybody familiar with any designs or serious concepts for beachcat killer tris around 18' LOA,square or oversquare overall length to beam ratio, with or without foil assist and designed to fly the main hull?
I know about the Exploder which is the only true "mini ORMA" type that I'm familiar with but it's 23'. I want to see if I've missed something in real high performance tri design in the vicinity of 18'.
Thanks in advance for any leads....

 

try this one

 

which one-your link doesn't appear to work

 

Try that now. It is 4.3m long for the centre hull and ALL up sailing weight is less than 60kg, the "plug" is in the final stages of completion as I wright

 

Foiler?

Darryl, the numbers sound exciting but I have web tv and can't open your file. Is this a foiler tri? Could you post a j-peg (or send me one or more ) - lorsail@webtv.net
Can you post more numbers? Thanks....

 

Try that now. It is 4.3m long for the centre hull and ALL up sailing weight is less than 60kg, the "plug" is in the final stages of completion as I write

 

What is a random statement? Try this for size!

Actualy, the ROH system is quite simple and robust. QUOTE - DOUG LORD.

Yeah and how is it done? Or do you think that you can make a claim like that and no-one will ever ask you to back it up. I challenge you to show the evidence that it is both simple and robust. Any refusal to post an answer to this challenge will taken as an "I don't really know anything about this, I just wanted to impress everyone that I had a firm grasp on the design concept, when in fact I had not a clue".

 

Hi Darryl, your 4.3m foiler tri looks very interesting. What are the more complete specifications including rig and details of the foils. On what do you base that the finished product will actually sail as per your own design brief? This is not intended in any way to denigrate the design, but merely to ask if you have based your concept closely on any other sucessful sail boats.
Regards, and best of luck. Sam