Marco said in another thread, “Personally I’m not convinced of the weight to windward concept, because you’ll have little to no chance to scim (or fly) the ama in normal sailing conditions—even Dave’s auto-flight can’t help you there.” He was echoed by Johannes; and many others in earlier threads, so I trust I’m not picking on Marco, but…

Consider for a moment the Atlantic proa (You may call them “weight to windward” if you like or “harryproas” or even “Norwood” proas and you’re welcome to talk all day about why one is not the other, but they’re all “Atlantic” proas to me. My mentor was Dick Newick so I grant him naming rights.  😉 

Atlantic proas can be hugely powerful beasts. In essence they are shunting trimarans with their windward hull and aka removed. An Atlantic proa has 2/3 the mass of an equivalently rigged and reinforced trimaran, and can generates a righting moment equal to a tri of nearly twice her beam. There’s nothing gentle or serene about them, they are serious brute-force toys, searching for max power with min structure and mass.

Do I maybe smell “raceboat”? Perhaps, perhaps not. Every boat has its Achilles’ heel and for Atlantic proas, that’s light wind performance. They are no better at ghosting than cats or tris, both notorious for poor performance in lighter wind

Pacific proas, OTOH, more closely hew to their namesake ocean; their much lower RM(max) means they cannot be driven as hard, but their ability to fly a hull, even in lighter winds, can yield startlingly good performance. Their structure is more lightly loaded than any other multihull—including Atlantic proas. When a Pac proa is running in its groove, quietly, serenely, under fingertip control it’s an awesome thing. Achilles’ heel? The obverse of the Atlantic of course. Pac proas suck in heavy weather. They must be reefed early and often, sometimes fill ballast tanks, even lie a-hull at night to avoid unseen squalls and potential capsize.

So, what if you could have both? You’d revel in your basic Pacific proa in lighter winds, then swap out boats when it pipes up and go high-speed bashing in your Atlantic—what a rush! How are we going to pay for two boats though? How about we don’t, and simply sail our proa in dual modes; ama to windward in light conditions and ama to leeward in heavy?

I’m serious; visualize a “standard” 75/25 weight distributed proa, with identical length hulls. We’ll need to arrange not only to steer the boat in both directions, but will need to do so when either hull is to leeward. If the hull(s) fly, this becomes more complex, but consider the advantages:

In Pacific mode the boat has 1/3 the righting moment. It’s easier to fly a hull (narrow-beamed racing catamarans in Southern California are demonstrating just what a light-air race winner this can be). With a functional auto-flight mechanism (mine or someone else’s; doesn’t matter. What matters is automatic adjustment to maintain flight, or “scimming” even as the crew moves to windward for more sail-carrying power). The boat will shunt normally, as does any other Pacific proa.

In Atlantic mode the boat has triple the righting moment. It now behaves more like the maxi-racer “square” trimarans, nearly as wide as they are long, with gigantic sail-carrying power and speed potential. With an auto-flight, the crew is free to move to leeward, reducing the giant RM(max) to encourage earlier hull flying, or back to the protected cockpit for some serious velocity. The rig might be sized to take advantage of this highest power mode, and set either reefed or split with one mast bare while the other does the work in Pacific mode. (Yes Virginia, we’d reef in lighter air, carry more sail as it pipes up. It’s a funny old world)

And how do we switch modes? By taking a simple one-time tack rather than shunt, putting the opposite hull to windward. That’s it, we’ve shifted gears. No ballast needs to move. No sliding, folding, extending or double-purpose “stuff” comes into play; the boat simply puts her other foot forward and *everything* is changed. That the boat can short-tack up narrow channels is a freebie; as is the ability to nose into a crowded dock, nuzzle it with one bow—under perfect control—then quietly back away when our lady has stepped aboard.

There’s more to consider, from lateral weight distribution (I can see arguments for 80/20, even 90/10; also for 60/40, even a 50/50 “asymmetric catamaran”) to where to put the accommodation, how to deal with the rig (and which rig???)  But it’s your turn. What do you think? Is there perhaps a proa for all oceans?

Dave

Stimulating post, Dave.

The rig might be sized to take advantage of this highest power mode, and set either reefed or split with one mast bare while the other does the work in Pacific mode. (Yes Virginia, we’d reef in lighter air, carry more sail as it pipes up. It’s a funny old world)

It is indeed a counter intuitive idea, even for a proa!

I have wondered about Atlantic proas over the years and thought about the savings in weight etc in removing the windward ama of a trimaran. But the windward ama and akas aren’t entirely wasted if they are providing extra RM if that is what you are trying to maximise (more sail area, more speed, more strength needed, more weight and around we go!) . So is it a case of diminishing returns or is it part of the reason that trimarans still dominate ocean racing? Or have I missed the point entirely? 😊

Mal’s Mi6 was designed to sail both ways and I think successfullly so. But maybe Mal can pipe in here.

I’m speaking from a place of ignorance here (I sail on a Newick tri), but I was under the impression that the primary advantage of the proa was the ability to build it lightly- the akas are not dealing with nearly as much force as with an Atlantic proa, tri, or cat.  A combo-proa would have to be built as sturdily (and as heavily) as an atlantic proa, so in light air (even in Pacific mode) it seems there would be a weight and speed penalty.  Lifting a hull would help, but displacement is displacement.

Feel feel to trash said opinion unmercifully.  (Oh, wait- this isn’t Sailing Anarchy . . .) 😊

Cheers,
Mitchell

Veeery stimulating indeed… And not hard to do, just beef up the iakos a good deal, and go for a higher displacement full-length offshore-trimaran-style ama. I think if you want to keep up with a high performance tri though, then you’re going to have to be able to fly a hull regardless of whether you’re in pacific or atlantic mode, and that makes things a bit more complicated; that smells like two sets of rudders in each hull to me, which would be pretty crazy… Alternatively you mount a pair of kickup-casette rudders on the iakos and make em long enough so they’re in the water regardless of who’s in the air. To me that slight performance loss would seem worth the reduction in complexity / build time.

As for the weight distribution, I’m inclined to say that making the ama as light as structurally possible would be the best course of action. When in atlantic mode the weight only hurts performance (higher total displacement), and in pacific mode it helps you get the ama up in the air more easily, increasing the envelope for good light-wind performance. There’s no benefit in deliberately making anything heavier than it absolutely needs to be (ama included), if you’re in PAC-mode in light/moderate conditions but it’s too light to tack an go AT, but you still need more RM, then you can still just add water ballast (or move something from the vaka to the ama); that’s still better than making the ama a leadmine a begin with. That said, I think what you were referring too was the potential of designing the ama to take some of the cargo on a permanent basis for instance, which would make hull-flying in AT-mode a bit easier…

I’d been thinking a bit on C-foils for Firstborne again lately. It’s complicated to get them right, and at first glance I was thinking “oh this idea of yours sounds great, but what about the C-Foils; there’s no way in hell I’ll build 4 of them”, until I realized that when you are sailing in light airs, you’re not going to be interested in C-foils anyway because you’re going too slow for them to be beneficial. So if you want a foil-assisted boat, then put the banana boards in the ama for use when you’re in AT-mode, just like the offshore racing trimarans. The really good part about this is that you could build your boat without having to worry about that now, and then you can always just build a new ama which features banana boards later on. So this setup overall would really lower the threshold for experimenting with a foil-assisted configuration!

There’s plenty of kinks to work out, but you’ve just about got me sold here… 😉

Cheers,
Marco

If you rearrange the very strong (and heavy) structure needed to resist the forces on the crossbeams of an Atlantic Proa, and use it to add length to a Pacific Proa, the Pacific Proa will always be faster. Maybe not absolute top peak speed in flat water in ideal conditions, but as an average in real world sailing.You would not routinely fly the vaka of a Atlantic Proa in any kind of waves offshore, but with a Pacific Proa with a leepod you would be flying the ama almost all the time. 
Pretty much what Mitchell says in the post above.

I disagree with the “Atlantic Proa - strong wind performance, Pacific Proa - light wind performance” comment above.
It is always a matter of optimization. A “monohull” can be a heavy slow Colin Archer or a foiling moth and anything between, in the precise same way a Pacific Proa can be a heavy deep V steel proa optimized for hurricane force winds down in the roaring forties or a ultra lightweight all carbon fiber foam core speed-machine flying more m2 sails the its weight in kgs. One of them will fly in a few m/s wind and the other will need 15 m/s winds just to do 5 knots of speed.

Cheers,
Johannes

mitchellhay - 09 June 2014 12:24 PM

I’m speaking from a place of ignorance here (I sail on a Newick tri), but I was under the impression that the primary advantage of the proa was the ability to build it lightly- the akas are not dealing with nearly as much force as with an Atlantic proa, tri, or cat.  A combo-proa would have to be built as sturdily (and as heavily) as an atlantic proa, so in light air (even in Pacific mode) it seems there would be a weight and speed penalty.  Lifting a hull would help, but displacement is displacement.

Feel feel to trash said opinion unmercifully.  (Oh, wait- this isn’t Sailing Anarchy . . .) 😊

Cheers,
Mitchell

I’m kinda in the same boat - an Atlantic-capable rig needs to be either unstayed (like Cheers & Harrys and much stronger) or stayed (somehow without interfering with shunting and much stronger).  If it is stayed, the amas would have to extend a fair bit (on both sides of the Vaka) to widen the staying base, and the weight advantage over tris keeps declining.  Also keeps you to pinhead sails to clear the stays.

It seems the design spiral (add strength, weight)  to deal with Atlantic proas keeps on coming back, no matter how you try to ignore it.  I have to give Rob Denney props because he’s just acknowledged that lifting a hull won’t happen and he builds for strength of the massive righting moment of his preferred (WTW) design choice.  He’s picked a set of compromises he accepts and sticks to his guns.  I personally like the design spiral of Pacific proas (lighter weight, less strength needed)  - but acknowledge this comes with caveat emptor issues as well. 

—
Bill in Ottawa

I think Dave is right about the pacific proas having less righting moment per unit of boat mass than cats or tris though, because with the pacific proas the CG is much further to leeward, which gives you a much smaller buoyancy-component in the RM—and less RM per unit of boat displacement would put them at a significant disadvantage performance-wise, if you’re really pushing.

Bill’s point about the rig is a good one though… The tri can have alight rig because it’s got a huge staying base and it doesn’t have to shunt the rig either, so a square-top main is not a problem. If you put the rig near the vaka on this proa, then you’ve got a bad situation where stays are concerned, when you’re in atlantic mode (which is also when the loads on the rig are highest, since that’s the high windspeed configuration)...

I hope Dave has some concrete numbers up his sleeve, but I think that per unit weight a cat will have about 10-15% more RM than a 75/25 pacific proa of equal beam. That said, the given pacific proa of the same weight can be longer (= faster) and if the lower structural loads also allow you to build significantly lighter, then maybe the 10-15% extra RM of the cat aren’t such a big deal anymore… I’m not sure if I’ve done the calculation correctly though—Dave? 😊

If the weight of our hybrid proa turns up somewhere between the cat and the pacific proa though, then maybe there’s a net gain to be had here…

The vaka has to fly though, otherwise the cats, tris, and pacific proas will probably all win out over the hybrid—that said though, if the cats and tris can fly their vaka, then the hybrid should be perfectly able to do it too, we’ve just sawed the windward ama off the tri and made it shunting after all…

I’m swamped at work just now, but am enjoying this immensely. I’l respond later tonight or in the morning. Some great ideas and *very* good questions arriving here. Please, keep it up!

Dave

The Europeans are heading off to bed mate—I’ll be eager to read what you’ve written when I get up tomorrow morning though. 😉

I think the rig may well turn out to be the real Achilles heel of this hybrid proa concept; it needs a nice and lofty rig like the high performance tris to make the most of the newly gained RM, but because the windward ama has been sawed off, the staying base has become a good deal narrower, and that means that the rig will become heavier, one way or another. High performance monohulls have lofty rigs too, but the tension in the stays and shrouds has to be a good deal higher because of the narrow staying base, and that means more weight, and they don’t have the shunting problem.

Essentially the question is: can we take a high performance tri, make it double ended and shunting, saw off the windward ama, still get the rig to stand upright (and shunt), and come out with a decent net improvement in total displacement? If yes, then we have a definite performance improvement over the tri at least.

I really like this concept a lot. For racing, I think the achilles heel of the design is the requirement of unstayed masts to manage the shunting AND tacking this design requires. However, some as yet unforeseen rig development could make the thing work, and then it would be unbeatable on the race course.

For general high performance cruising, you could accept the unstayed mast and even consider it a benefit for all the usual reasons that unstayed rig fans use. Such a boat in Pacific mode will still not be as lightly built and efficient as a true Pacific proa, but again, for cruising, you might want sturdier scantlings to begin with, so the weight penalty of the stronger beams and larger ama would not be such a penalty.

Still have four, yes 4, rudders though. But that’s just the price you pay to fly the BIG hull. Man, it would be epic!

In my experience weight to windward has ONE single advantage and that is more RM. With the added weight far out to windward comes a lot of problems with the balance. When the low mass aka (to lee) dives into a wave, all the heavy mass far out to windward (very high moment of inertia far from CLR) will try to rotate the proa down wind and the twisting loads on the crossbeams resisting this will be huge. One of the main advantages with a Pacific Proa is the dominance of the vaka. It will move very smooth, like a very slender monohull, with the ama just along for the ride. A catamaran or a shunting catamaran (equal length hulls - Atlantic Proa) has a much more jerky and twitchy motion since the two hulls always “fight” each other since they are never in the same part of the wave. Each hull trying to push or pull the other hull in some strange angle relative to the CD.

Try attaching two 3 meter long crossbeams to a bicycle and have a friend sitting out there. Ride the bike fast down an uneven slope and try to steer and/or stop the bike with your regular break and wheel, while you try to keep the friend flying a meter above ground. Then compare this “experience” with doing the same thing with your friend sitting behind you on the luggage rack while he is actively counterbalancing the crossbeams to get a high sideways stability through the moment of inertia of his mass and the mass of the crossbeams.

Cheers,
Johannes

When sailing with a catamaran or trimaran race we always try to keep as much as possible the horizontal platform just above the water surface. Too high, we flirt with danger.
sake of an Atlantic proa is to browse as often as possible flat! Ideal for smooth sailing!
Now we know they built trimarans for sailing with three hulls out of the water constantly over 20 knots! It is good for adrenaline! a trimaran sailing on one hull is a great art design and navigate! But even with 10 ° outside temperature you sweat!
The proa race does not have a good reputation in Brittany (France) precisely because we conceive the big trimarans right now and it runs fast! ...I hope that one day we will think.

I couldn’t resist sharing a few more things that went through my head concerning the rig…

In theory it doesn’t have to be unstayed. If you are racing around the cans, on an upwind-downwind or triangle course or whatever, then an unstayed rig is probably best. In light airs you’d go all pacific, but with the wind up a bit you’d probably want to sail upwind as an atlantic proa, and downwind as a pacific proa (so that your crew can dance around on the lee pod to get the ama flying even though you’re going downwind—here’s to a light ama! 😊 ).

If we are not racing around the cans however, but have a longer course, then the situation changes. I would argue that a shunt should be quick, but a tack doesn’t have to be nearly as much so, since you’d only tack when there’s really a change in wind conditions, or you go from upwind to downwind, which would involve sail changes anyway. I propose the following solution:

- The rig is offset a bit toward the ama like on Russell’s boats
- When in Pacific proa mode, you have two shrouds running from the masthead to each bow of the ama
- When running in atlantic mode, you have a stay running to each bow of the vaka (remember that the mast is offset a bit toward the ama), and a shroud running to the anti-capsize pod (it’s a ‘weather’ pod in ATL-mode)

To transition from one mode to the other, you raise / lower the shrouds using two halyards (one to which the two pacific shrouds are connected, and the other halyard for the shroud and the fore/backstays for the atlantic configuration), so essentially you swap your entire stay/shroud set. The ‘standing’ rigging which is currently not in use, can be kept at the ready, the halyard right along the mast so it’s not in the way when shunting. With this setup there isn’t any rigging in the way if you want to shunt, regardless of your operating mode. The tacking takes a bit longer, but now your rig doesn’t have to be unstayed.

Cheers,
Marco

PS - @Johannes: The record-holding offshore tris overcome the difficulties of which you speak somehow too…

PPS - I don’t think having a permanent anti-capsize pod would be a good idea on a hybrid proa, since it’s bound to slam pretty hard when it’s on the weather side. Either one makes it a lot smaller, gives it more clearance (not possible without a significant increase in freeboard on a small boat like firstborne though), gives it a shape better suited to getting hit by breaking waves (Cheers had a pod too…), or you drop it altogether and go for something like an inflatable safety ama… That’s more of a minor detail though.

Marco,

The main problem I see with your proposed “swap-the-standing-rigging” concept is that if for some reason you mess up the nice choregraphy that has to take place when you go from Atlantic to Pacific mode or vice-versa, the mast goes down…
And you will mess it up one day…  😉

Even if it is not a complete mess up of “ooooops, I released the old rigging before I got the new one taught”, if you simply have both rigging slack for some period of time, having the mast and the sails bouncing back and forth, right and left for a few seconds will most likely be fatal due to the humongous shock loads that would generate.

Soooooo…. not trashing the idea, but I would rather have what I would call a “semi-unstayed rig”. I would have the rig with some bury, a socket in the main hull, and 2 mast-bearings, etc, so when everything is loosen the mast still stands up. A good engineer should even be able to size it so it does not break under load, the sail shape may be a disaster if you sheet it before you tighten up the new standing rigging, but the mast does not fall down; just release the sails, tighten the new rigging and sheet it again.

My 2 cents…

Laurent