Why so few proas?

Proas- the original multihulls- are rather rare these days. Which is really quite a shame.

A proa, for the uninitiated, is a laterally asymmetrical multihull: one hull is smaller than the other. Proas, at least in the strict definition, are also double-ended, switching bow for stern in a manoeuvre called a "shunt" when ordinary sailboats would tack. There are, of course, proas that tack in the conventional manner, although these are more commonly called tacking outriggers.

The easiest way to visualize the evolution of a proa is simply to add a single stabilizing outrigger to a dugout canoe, and this is likely how they originated in ancient Pacific cultures. From an engineering standpoint, though, one can easily morph a modern trimaran into a proa (simply remove the redundant windward ama and extend the hull to make it double-ended). Even a modern canting-keel monohull can be morphed into a proa (cant the keel all the way to 90 degrees, and since it's now mostly clear of the water, make it buoyant- and, of course, double-end the hull). In either approach, certain efficiencies are gained in the design: a simpler and lighter structure, a longer waterline (thus a faster boat) for the same weight and build effort, and a few extra degrees of design freedom.

For a more involved description of the proa, the reader is referred to Wikipedia, Proafile, boatdesign.net, Rob Denney and of course the international proa community's Yahoo group, among other resources. My purpose here isn't to rehash that information, but rather to question why the proa concept- despite undeniable engineering merits- holds marginally more than 0% market share.

What are those engineering merits? Speed, for one. R. M. Munroe hit 18 knots in the first 9 m proa prototype he hacked together from second-hand sketches- in 1898. More recently, Russell Brown's 11 m Jzerro- a liveaboard cruiser- has reportedly hit 21 knots, Rob Denney's weight-to-windward Harryproas frequently clock speeds in the teens, and Inigo Wignen's 21.6 m Gaia's Dream is predicted to routinely knock off 240 mile days. The combination of extremely high length/displacement and length/beam ratios with enormous righting moment gives a high power, low drag configuration with no clear "hump speed" to hold it back.

Structural simplicity is another strong point of proas. The nasty torsional loads that cats and tris suffer are not absent, but some of the rig loads are, which can greatly simplify and lighten the structure. And with one fewer hull than a trimaran (and half as much crossbeam), build time and cost are reduced compared to the proa's main competition in the speed department.

From a designer's standpoint, the proa layout opens up a host of new options that would otherwise be pre-determined. Do you put your accommodations to windward, or to leeward, or do you put the social functions into one hull and the private space in the other? How do you distribute the displacement between the two hulls? Since you're using a crazy design anyway, which of several dozen crazy rigs will you use, compared to the handful of basic types seen on more conventional boats?

Most commonly cited proa downsides are easily resolved with some clever engineering. 360-degree or retractable rudders, rigs that can be swung and shifted when the boat changes direction in a shunt, and retractable pod-mounted engines and propellers are complex to design, but relatively straightforward to implement.

That leaves one real and one psychological downside that are keeping proa innovation in the hands of a small group of enthusiasts, rather than production designers. The real downside is length. Simply put, a good proa will almost always be far longer than a mono, cat or tri with comparable accommodations. That's part of how proas get their speed and efficiency; if you build them short and fat, they will perform like pigs. But if you proportion them correctly, they end up more than twice as wide and longer by half than monohulls with similar living space. So either the dock fees triple, or the boat's a sluggish dog- hardly an acceptable outcome for many people. The solution is the one most cruisers seem to prefer anyway: lie at anchor and take the dinghy to shore. It does, however, preclude proa ownership for the majority of casual boaters who are forced to be marina dependent.

Arguably the more important downside, though, is that yachties are traditionalists. After Herreshoff's catamaran Amaryllis roundly trounced the racing monohulls of the New York elite in an 1876 regatta, it (and anything like it) was banned from racing, a mistake that took the better part of a century to rectify. When the simple plywood multihulls of James Wharram and Arthur Piver gave 1960s hippies the opportunity to get out and cruise the world, traditional yacht clubs were so shocked and offended by the radical new boats and their non-traditional crews that multihulls were widely tarred with the "cheap junk" brush, right up until the charter industry realized how much profit could be made by dropping a four-bedroom condo onto a pair of long, slim hulls. Even with all this change, anything new is still greeted with suspicion in many circles. Proas are undoubtedly a much bigger change from the "norm" than cats and tris were, and will face similar if not tougher difficulties in the transition from beach toy to serious cruising boat.

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Comments

Proas

hi. my brother is turning his 30 foot pacific proa into tacking outrigger due to difficulties handling it by himself when shunting. Ini's second 40 foot proa was a tacker for similar reasons (but it did sail him from holand to aussie). There are alot of problems getting them to work properly, more than seem to appear at a first look. But if sorted they definately seem to offer the most speed and seaworthyness for the doller.

Ben

tacking outrigger

Hello Ben

Do you have any information on your brothers proa/tacking-outrigger

I have a website devoted to that subject. Your brother may be possibly interested in what others have done in the genre. Additionally myself and I think others would be interested in your brothers boat.

my website is tacking-outrigger.com

If your brother does not have a webpage, I could make one for him. This is just a polite request. Not a demand and I am not insisting at all.

regards, Peter Evans

It takes a few generations of development

Matthew's picture

I think you're right, Ben, that there can be quite a few problems involved in getting a proa to work properly. I don't doubt that there are quite a few that have been tried that performed like dogs and were a pain to handle.
On the flip side, the same can be said for hundreds of examples of early monohull cruising and racing yachts, and of some of the recreational multihulls of the '60s and '70s: complex, finicky designs that were hard to handle short-handed. I think it's more about a concentration, or lack, of development effort than about a fundamental flaw in any particular configuration.

Proa Monohulls

Hi Matthew, I agree, and I thought it was a good article you wrote. I think they could work very well for someone thats willing to tinker and get them right,and I suspect the ulitimate seaworthiness of them with a drogue off the outrigger would be very good. Interestingly two devout multihullers I have talked to hate proas more than they dislike monos.

I still hope My brother will Set his up so it can be shunted for long legs. But he also needs the ability to tack with the shifty winds around here. I think any proa would benefit from being able to be tacked for short legs to windward, It would take all the pain out of being caught aback. By the way Ini reckoned his 40 foot tacker was much better with the outrigger to windward in pacifc configuration rather than atlantic configuration.

I wonder if a proa monohull would work, it could have shallow draught and a big water ballast tank on one side, I have seen a few designs around. But I see lots of problems with rudders and engines.

Cheers

Ben

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