Atlantic vs. Pacific Proas
Having your cake and eating it too
If there’s one topic of perpetual interest among proaphiles, it is the debate between “weight to leeward” or “Pacific” proas vs. “weight to windward” or “Atlantic” proas. Is it better to carry most of the weight to windward, or to leeward, or perhaps just keep it more or less centered?
To be clear, we can blame Richard C. Newick for the debate, since it was he who came up with the Atlantic proa in the first place, with his groundbreaking Cheers - the “giant killer” that came in third in the 1968 OSTAR. Unlike all proas until Cheers, Newick placed the ama to lee and the rig to windward, concentrating all the ballast to windward and thus multiplying the righting moment.
As a trimaran designer, Newick no doubt noticed how the windward ama of a tri is always redundant, merely adding weight and windage and not providing any real benefit. With Cheers, he designed a “one ama trimaran”. Genius.
On the other hand, we have ancient Pacific Island culture weighing in on the Pacific side, the long and slender canoe hull, elegantly counterpoised by the ballast ama to windward. While the approach is somewhat counter-intuitive to Western ideas about sailboat design, it is true that up until WWII and the invention of marine plywood, the fastest sailboats in the world were traditional Pacific sailing canoes. It was Woody Brown who brought the two together in Manu Kai, the first modern catamaran. Russell Brown (no relation to Woody) is the most well-known and successful advocate of the modern Pacific type.
It occurs to me that with a proa, it’s not actually necessary to choose between one or the other. What if we designed a proa to sail equally well in Atlantic or Pacific mode, and if we did, would there be any advantages? Imagine a proa that was designed to sail in light weather as a Pacific proa, but in heavy weather as an Atlantic proa. Apparently, I’m a bit late on this, see Malcolm Smith’s Mi6:
The outrigger is the same length as the main hull for speed and also to provide maximum diagonal stability in Atlantic mode. The construction technique is identical to that of the main hull and also incorporates a rounded chine plank.
The outrigger has enough volume to carry twice the displacement of the boat. It is however much narrower than the main hull and has less rocker or spring in the keel line. The difference in hull shapes is intended to make the boat as efficient as possible through it’s entire speed range. In light winds it would be sailed in Pacific mode, flying the outrigger as much as possible to reduce wetted surface. The main hull with much of it’s volume concentrated around midships has a lower prismatic coefficient, Cp, providing lower resistance at lower speeds. The outrigger conversely has been designed with a high Cp. The ends are relatively more voluminous than the main hull, giving lower resistance at higher speeds. Therefore, in heavier winds, the proa would be sailed in Atlantic mode, with the outrigger becoming the major load bearing hull, possibly even to the point where the main hull is “flown”.
It should be noted that the above idea is not unique to proas. Trimarans work in much the same way without even thinking about it but pay a price in terms of weight, windage and cost of the extra hull. Conventional catamarans do not have the advantage of the ability to select the right hull for the right conditions, and with two identically shaped hulls better suited to higher speeds, are not often noted for their light air performance.
Bingo. A yacht suitable for both light and strong air, just choose the side that suits you!
This is something I’ve been going back and forth on. Stirred it up a bit back on the Yahoo group, and still stir it in my head. The advantages to the Atlantic layout that I can see are simplifying balance issues at the cost of wetted surface in lighter winds. With the Atlantic, the thrust of the rig tends to fall between the drag of the two immersed hulls, helping to alleviate the need for large foils at either end of the boat to balance CLR and CLE. With the Pacific, the rig falls to one side of all of the drag, which is why the rig is so far forward to get everything to balance. Denny gets around this with a really straight keel,the whole the Baelstron rig which rotates a large part of it’s area to windward and big rudders. The drawback to the traditional rig is the work in shunting and the issues with being caught aback. The other cure for this is moving the rig to windward, but now you have to support the mast on the cross beams, which really complicates the structure.
The problem I see is balancing everything for the big swing in thrust versus drag for the 2 modes. It can of course be done with foils that go up and down or with a schooner rig, but that complicates the boat. S single sail is also more efficient to windward and simpler to shunt or tack. I personally am looking hard at what James Brett did and what Terho did rigwise with ping pong, then moving it a little way to windward of the Vaka. I want free standing to alleviate aback issues or to make changing from Atlantic to pacific to tacking modes are a quick and simple thing. The more central/non variable I can keep the thrust vs drag balance, the better the boat will go between the various modes. Gary’s latest rudder design shown over on his blog looks fantastic for a boat designed to be this confused. able to kick up wither direction and simple to raise and lower to affect balance. I just need to get the mast support component ironed out in a lightweight fashion at reasonable cost and minimum complexity.
I’ve though about just building a catamaran that’s symmetrical end to end as well as laterally, rig and rudders on the centerline, Rig some king of JUnk/Bolger AYRS hybrid. Then I remember that I was attracted to the proa in the first place because I only had to build one major hull, saving time, money and weight.
Thank god I don’t have the time or space to build yet. I’d actually have to come to a decision 😉
Hi Tom, sounds like you’re going around the design spiral enough to get dizzy. 😉 I think you are on the right track with the junk rig or maybe a Bolger/AYRS square sail because the CE doesn’t shift around as much during the shunt, so less shifting of boards to compensate. This is the way I’m leaning, and the rig is naturally suited for a free-standing mast, so the boat can easily sail in either Pacific or Atlantic mode.
I really like the option of being able to tack - it would make a casual day sail on the bay a lot more casual, as well as remove fears of getting caught aback.
Michael,
Do you know if anyone has tried a version of the ARYS sail with straight battens and the camber developed ala Arne kvernland in the fabric panels? I would hope that would help it actually “luff” and depower. Addionally, the head and luff tension would have a different path because the tension would HAVE to be along the current luff if using the cambered panels. I’ve also considered setting it up like a Baelstron with the downhauls fixed to both ends of the “boom”. this could have eithe one or two adjustable downhauls so the sail would never “get away” and take flight like occasionally happened with the original version (apparently a very dangerous situation).
Tom
I’ve not heard of anyone doing what you propose. However, I HAVE seen a working model of an AYRS square sail once. It was called the “Benz Smart Sail” and I saw it at, (I think), the Miami Boat Show in the 90’s? Anyway, it used a lower boom as you suggest, so that the sail couldn’t get away and do an unintentional wingover.
In hindsight, I think that rig was the perfect proa rig, I just didn’t appreciate it at the time. Obviously no one else did either. I think he got far enough to equip a Tremolino with it. Checking… yes, he did.
Hi Michael,
made some thoughts about 10 yeares ago for a Benze Rigg adapted to a proa. May are something interesting in it. Sorrily mostly written in German, but Google Translate may help, and there are some pics too:
http://www.multihull.de/proa/p_Bolger.htm
Terho Halme’s “Ping-Pong” shows a similar configuration:
http://wikiproa.pbworks.com/Terho+Halme’s+“Ping-Pong”
Othmar,
Love your P8. I’ve considered learning German just so I can cruise your website better. I’d love to hear more about how P8 is working out in english somehwere, maybe update the article here? I’m also curious how much sail area you ended up with and how adequate you think it is. I started a thread on that subject a day or two ago.
Tom
Michael,
Do you know if anyone has tried a version of the ARYS sail with straight battens and the camber developed ala Arne kvernland in the fabric panels? I would hope that would help it actually “luff” and depower. Addionally, the head and luff tension would have a different path because the tension would HAVE to be along the current luff if using the cambered panels. I’ve also considered setting it up like a Baelstron with the downhauls fixed to both ends of the “boom”. this could have eithe one or two adjustable downhauls so the sail would never “get away” and take flight like occasionally happened with the original version (apparently a very dangerous situation).
Tom
The last rig on P52 was headed in that direction, bidirectional clubbed jib, it was never out in strong conditions but finished a Texas 200 after repairing my misapprehension that gorilla tape could do anything (anything doesn’t include sail heads).
I’m one of those idiots that can’t leave the bidirectional proa sail alone. It started with ACDC and continued on P52 after an excursion into crab claws. I’m of the firm opinion that the problem with ‘runaway tacks’ disappears when you go to a sliding tack shuttle with separate sheets. The sliding tack resembles an inside out parallel bar with the tack shuttle sliding from one end to the other while the boom maintains the same fore and aft location in relation to the hull. A serious extra benefit is that you can change that lateral relationship if desired which means you can have a balanced downwind sail just by adjusting a line.
Skip
Othmar,
Love your P8. I’ve considered learning German just so I can cruise your website better. I’d love to hear more about how P8 is working out in english somehwere, maybe update the article here? I’m also curious how much sail area you ended up with and how adequate you think it is. I started a thread on that subject a day or two ago.
Tom
Hi Tom,
there is a short description about building KALAPUNA here in proafile: http://www.proafile.com/archive/article/kalapuna
Also there are two videos at YouTube available:
http://youtu.be/UJ4ubpzE0BI and http://youtu.be/9QBCwMsplo4
About my sail area I will answer in your thread PROA SA/D & BRUCE NUMBER
Othmar
just a realised that no one has mentioned malcom tennant with regards to proas. he did design’ Disco Volante’ (http://www.tennantdesign.co.nz/index.php?page=disco-volante) - a proa that seems to have potential as either pac pr atlantic proa… i haven’t devoloped an opinion as yet, just wondering if any one else has.
cheers,
Doogs.
I love the name! 😊