The idea that a 40' proa will be equivalent of less in weight, cost, and time to build than a 30 foot cat, both boats having equal usable internal volume is in my opinion unrealistic. Materials and weight tend to increase with the cube of the length on a boat. The estimate of a 25% savings in weight between plywood and foam sandwich without compromising structural integrity seems to approach reality IF the boat is designed specifically to get the max weight savings by utilizing the material to the best advantage.
The fact remains that I simply do not want a 40' boat as a single hander, or as a builder. I'm somewhat open minded, but the fact remains that the boat I want to build is a 30' cat, and I do not see anybody swaying me on this in the foreseeable future.
The idea of doing a flat development and merely folding flexible corners may be feasible in some situations, but it clearly is not in this case. Anybody with the most basic sense of geometry can see this. The stuff of fantasy. What I see as the most realistic build system is to build a three dimensional mold of an entire hull side on it's side on the floor or a table using temporary formers, stringers, and flat sheet material with a suitable gloss surface, the intersecting corners being radiused, and sanded smooth, as well as the joints, and any fasteners. The entire thing coated with a mold release, and the layers of the sandwich added and infused........... no small undertaking. The knuckle.... thanks, that was the word that I was looking for..... and half the bottom, more or less lock in the contour. Each mold would make two hull sides, and the formers would be reversed to make the other mold. The bottom could be made in halves as part of the two hull sides, or made flat, and added later, resulting in two full length seams instead of one. I like the one seam, as it would be covered by the 6" sacrificial wood beaching keel I envision. Not all beaches are sandy and rock free.
The second alternative of course is to just build 3 long flat panels for each side of each hull, plus the bottom and have full length seams. A far simpler method, but far more finishing labor.... at least 6 seams in each hull, plus the seams for attaching the coach roof bridge deck, and bridge deck cabin, etc........... "idiotic infusion"???
Speaking of "flat development", developing a hull shape and formers that is compatible with flat sheet construction, is an interesting challenge. I've always had great respect for people who design smooth shapes in three dimensions, and that respect is much greater than it was just a few days ago ;-)
Your arguments for the Harry Proa are falling on deaf ears ;-)
As far as carrying sail outboard, a reach beam reach is about the only point of sail where the main portion of the sail would be carried outboard. In ideal sailing conditions there is no chance of a wave catching a wave, but conditions are often less than ideal. I would want to be able to shunt if I had a rig like Robs Aero Rig, or the junk rig I'm planning to use, on a single mast in one hull so that I could sail with the long end of the boom over the boat. I will have a low aspect ratio rig & relatively short mast, which means that the sail will be fairly square, and the boom long.... about as long as I can get away with and still be able to sheet with a decent angle. My idea is to sheet through a traveling block from the two outboard aft corners of the boat. As there is no need for down pressure as on a Bermuda rig, this can all be fairly light, and travel from one corner to the other via a line rather than a track.
I've been toying with the idea of completely reversing the sail. As the mast on a junk rig is not the leading edge of the sail, and in fact on the Aerojunk is not involved at all, I don't see a lot of reason why the head sail needs to the the smaller portion. Sheeting loads would be double if sheeted to the short ends of the battens, but that's not a bad thing and still far less than on a bermuda rig where there is zero balance area, and tension is needed to shape the sail. It might look a bit strange to have a backward sail, but realistically if one looks at a masthead Bermuda rigged boat, in many cases the head sail is larger than the main. The wind doesn't care. The important thing is that the camber is distributed ideally for max efficiency. One big advantage in doing this is that a tension based automatic sheet release could be used so that if one was napping below, and was hit by a sudden violent gust, the sheet would go free in stead of the boat being knocked down.
H.W.
On 05/26/2018 10:36 PM, '.' eruttan@yahoo.com [harryproa] wrote:
|> How do you compare a cat and a tri? Per foot? Or displacement? Or cost? Or accommodations?
|>
| I look at my 30' parameter, and the most I can get from it in a multihull.
My point is, you should question this premise.
There is nothing about a longer hull, specifically, that costs more. A longer, lighter hull does not need a bigger sail than a shorter heavier one. It CAN carry one, but does not Need it. In fact, a longer lighter hull can do more with less sail. A longer lighter hull has, generally, less wear and tear than a smaller heavier hull because its weight is not being used against itself. IMHO
While you make a good point about paint, that is a trivial cost. Rob recommends house paint, as it is light and does the job.
|The cat has narrower hulls, but two of them, a far larger cockpit, and the bridge deck cabin on a level with the cockpit... .
Do you care about where the space is? You have stated you want an open cabin. Is the Cruiser 50 not a big enough cabin? The Ex40?
| I look at payload, not just displacement. Dead weight / excess boat weight is a liability. It means more drag, slower sailing, and a bigger rig, larger motor(s), etc.
Every harryproa you would look at has as large, or larger payload. And is significantly lighter. But those options are only available if you question 30' loa.
|technology we have today such as AIS.
AIS and autopilot make things easy, I think. Feels like cheating. Still not sure about sleep sailing.
|Asymmetry doesn't bother me, in fact I'm attracted to it.
|Proas are in fact just asymmetric cats........... or
vice versa.
My opinion?
Cats are relatively symmetrical port/starboard.
Harryproas are relatively symmetrical fore aft.
Its not asymmetry as much as a different axis of symmetry. And, I think, that different axis makes possible to put the people in the lowest motion position.
|However it really doesn't work to put the mast in one hull of a cat.
It does not matter, but you don't explain why.
|The desire to always have the sail over the boat, and not reaching far outboard to catch waves, leads into shunting, which is OK also. Rob's variant of having the accommodation hull without the mast, and the mast hull is a good one IMHO.
Afaik, Rob sails all the time with the sail over the waves. Rob, have you caught one yet?
I don't see how wave catching and it's avoidance leads to shunting. I think shunting comes from always keeping one hull to windward, the other to lee.
| I have reluctantly come to the realization as you state that it is
|desirable to start from the ground up to achieve my goals,
If you don't question the right goals your redesign will lead to the same thing others have done. Be careful when accepting premises.
|Starting from the ground up is not completely accurate, as I intend to borrow ideas
Don't borrow, steal!
| Pete Hill's Oryx improved on these by incorporating a ridge / wing, or whatever you want to call it,
Knuckle?
|The portlights will be higher to allow good side visibility from the bridge deck cabin.
| The challenge here is locating the mast.
And this is where I dropped out, as I said .
|I don't see how one can build half a hull in one shot on a flat table.
I may be out over my skis, but I think it goes, do a big flat infusion, using foam to make the flat parts flat, and solid laminate in the corners, which will bend. Recesses where the bulkheads go, and infuse. Then wrap that infusion around the bulkheads as you edge glue the bulkheads in place in place and male/female glue the closing tabs.
But that's just a guess. Ask Rob.
|> I also have a limited objection to the assertion of ongoing higher
|> costs of a bigger boat. While generally true, there are some
|> exceptions, which Rob has optimized. Assuming a typical Denny design,
|
|> what costs are increased for a bigger boat?
|>
|> The hull is lighter, so more easily driven. The durability and wear
|> should favour the lighter boat. The only real direct cost I can think
|
|> of is the marina fees, to which Rob has an integrated generous tender
|
|> to mitigate. I can think of no other costs.
|>
|> Finally, I assert a bigger boat can be cheaper than a smaller boat. I
|
|> dare you to compare BOM's, for just the hull costs and sails, for the
|
|> most similar accommodations to the designs you stated.
|>
|> Then look at the one with the most similar payload.
|>
|
| Larger rigs mean heavier everything from cordage to blocks, to larger sails,
Who said larger sails? Again, larger lighter hulls don't need larger sails.
|Likewise there is more bottom to paint and maintain, and more top and interior.
Rob has said house paint once every 10 years. And cleaning the bottom of a 10" draft is stupid easy. Its playing in the water at the beach for a bit every once in a while. Iirc, Rob says it is 20 min once every 2 weeks. Certainly easier than a 40" draft boat, even if it is much more square feet.
| Heavier ground tackle, which costs more to buy and maintain,
Hull is lighter. Not need heavier.
|even more fenders, etc.
Did I read rob uses pvc pipe? Integrated into hull?
|Bigger engines,
Lighter hull, but this may be legit, in that windage may need bigger motor. But I cannot say for sure.
|more fuel to buy and store, etc.
Lighter boat sails in lighter wind. Less fuel
| Then there is a greater likelihood that some lady will be attracted to a guy with a bigger boat, and all the attendant expenses that go with that ;-)
Who's column does this argument go in?
If faced with this problem, I might suggest you explain you are compensating for something.
No, you will never sell me on the idea that a
|larger boat may not cost more on an ongoing basis.
|>
|>
|> H.W.
|>
|>
Posted by: StoneTool <owly@ttc-cmc.net>
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