Tacking Proa (for lack of a better term)

Discussion in 'Multihulls' started by Owly, Nov 27, 2020.

  1. Owly
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    Owly Senior Member

    The Pacific Proa has the ama on the windward side, and the Atlantic Proa has the ama on the leeward side. I have wondered if anybody has built a "Tacking Proa", where the ama is on the leeward side on one tack, and the windward side on the other tack. Tacking rather than shunting. One the one tack, the displacement of the ama provides the stability, and on the other, the human cargo hikes out and rides the side deck. I've never read of such a thing. The mast of course would be in the larger hull.

    H.W.
     
  2. Rumars
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    Rumars Senior Member

  3. rob denney
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    rob denney Senior Member

    A better description is a biplane catamaran with a mast missing. There are several of them in beach cat sizes, none that I know of longer than 20'.
    Strange, as it is an excellent way to get an unstayed mast in a cat, with all the benefits they provide.
     
  4. bajansailor
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    bajansailor Marine Surveyor

    A pal of mine here had an AMF Hilu in the early 70's, and I occasionally went sailing on it with him - it was a lot of fun to sail. I don't remember ever capsizing - even when sailing with the outrigger to windward, the crew sit to windward and are very effective. Even us little kids who didn't weigh much!

    Hilu - Wikipedia https://en.wikipedia.org/wiki/Hilu

    https://sailboatdata.com/sailboat/hilu

    AMF/Alcort Hilu sailboat vintage ads https://my2fish.wordpress.com/2012/01/17/amfalcort-hilu-sailboat-vintage-ads/

    AMF Hilu advertisement.jpg


    AMF Hilu specifications.jpg
     
  5. oldmulti
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    oldmulti Senior Member

    Owly. The most successful tacking proa I know is Arpex. A Brazilian build launch a few years ago about 30 foot long. The guy has a good web site somewhere. Attached are a few jpegs.
     

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  6. bajansailor
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    bajansailor Marine Surveyor

  7. garydierking
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    garydierking Senior Member

    The tacking outrigger has been around for at least 1000 years as it was and is the dominate type used for small craft in Tahiti and Hawaii. I have been designing and building them for the past 20 years and there are now several hundred of them sailing.
    Outrigger Sailing Canoes http://outriggersailingcanoes.blogspot.com/
    Ulua Outrigger Sailing Canoe https://uluaoutrigger.blogspot.com/
    Va'a Motu Outrigger Sailing Canoe https://vaamotu.blogspot.com/
    Wa'apa Outrigger Sailing Canoe https://waapa.blogspot.com/
    Tamanu Outrigger Sailing Canoe https://tamanuoutrigger.blogspot.com/
    https://www.amazon.com/Building-Out...7170409?ie=UTF8&s=books&qid=1180055974&sr=8-1
    Tacking outriggers can be adapted with a safety ama that doesn't touch the water unless capsize is imminent or made into double outriggers.
    [​IMG]
     
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  8. Owly
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    Owly Senior Member

    Thanks for all the responses..... My ignorance is showing ;-) ..... I had not encountered these in my reading. I didn't know what to call something like this..... Looks like they are not all that uncommon In looking at the ones with shelter on the main hull, I was thinking how inconvenient it would be to have to leave shelter in a storm or intense sun on one tack. One advantage of shunting on such a craft is that if it is an Atlantic proa... shelter on the windward side, you always have shelter from the wind in addition of course to shade. Another decent argument for shunting.
    To add just a touch of madness to this concept, imagine a flip down foil at the outer edge of the small hull. The foil would be for down force in "Pacific mode" or to lift the hull out of the water in "Atlantic mode". The angle of attack of the actual foil can be controlled by the helmsman. On the Pacific tack, you could either hike out, or drop the foil and sit in the shade and apply the down force using the foil. It could even be set up so deck angle would control angle of attack using something as simple as a weight on an arm. Of course if the foil stalled due to too much angle, you would capsize so fast that you would not have time to react. It would be like driving a 737Max into the ground... except for the opposite reason... but there are ways other than computers to manage stall ;-) The Ercoupe did it by simply limiting elevator travel. Using this system, you could fly the ama on both tacks, in fact the ama would have little purpose once you were moving any speed.... just a heel limiter.

    H.W.


    Again forgive my ignorance if you will....... I've never taken proas seriously in the past. The look precarious to me, and I dislike unexpected cold water baths! I sudden wind shift or large gust and you could be in the water. I've never sailed one or even watched them sail except on Utube. Presumably in a knockdown the sail unloads enough that it wouldn't take much of a "safety ama" to stop you before 90 degrees. Obviously people have built virtually every imaginable kind of sailing craft....... I've just never paid much heed to the various types of outriggers other than shunting proas, and not much to them.
     
  9. garydierking
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    garydierking Senior Member

  10. Owly
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    Owly Senior Member

    This is exactly what I was thinking of..... Like the designer, I've been involved in aviation.... either building models as a child, or flying fixed wing aircraft, or ultralights, for over 50 years.. I've even built my own. The concern I have watching the video is the need for active control constantly.... If you are the slightest bit careless and that foil comes out of the water or stalls when the ama is to the windward side, only very quick thinking and reaction will keep it from going over... you can't put it back down in the water once the boat heels beyond a certain point. Aircraft can be trimmed for hands off flight quite easily, and recovered from any attitude if you do get careless (or playful). I'll never forget the first time I put a plane in a spin (on purpose).
    For speed and thrills the foil would be great!.... For longer sailing, I would want to have a control that would allow you to dial in the angle of heel, and it would maintain it, perhaps using a pendulum weight inside a housing to operate the foil via a trim tab.
     
  11. Robert Biegler
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    Robert Biegler Junior Member

    I had a Raptor for a few years. The one time I capsized it was when I noticed that I had made a mistake in rigging up the boat, crossing some lines, and tried to sort it out on the water while the foil was to weather. Without boat speed and corresponding flow over the foil, the weight provided too little downforce and over I went. Also, when tacking onto starboard tack, I would have to be careful sheeting in so that I didn't overload the foil at low speed.

    A Bruce foil with modest aspect ratio might give you more stability at low speed, because leeway makes it hook in. Only, members of the Amateur Yacht Research society built a few in the 60s an 70s, and found they were vulnerable to popping the foil out in a seaway when the foil was to weather. Haagedorn suggested putting a hinge on the foil and curving the foil, but intended that only for a foil to weather on a proa. Fritz Roth has implemented this, and reports it works well. Although daysailers of that type have been built, the only video I know of are of models: https://www.youtube.com/channel/UCR2PQOlWxJtJWS_Aq6DRSQA But note that the model stays upright in surf and with wind in the sails even when not moving forward. The Raptor's foil doesn't do that.

    The simplest way to apply the same idea to a tacking outrigger should be in Figure 15 of an article I wrote for AYRS some years ago: https://www.ayrs.org/catalyst/Catalyst_N23_Jan_2006.pdf That article also has some calculation of stability curves.

    I never built a boat to that design, though. I am currently building a radio-controlled model to try out a few developments of that idea next year, and I hope to try one of them on a sailing canoe, too.

    One thing that worries me about this concept is that you have highly loaded moving parts. If you design so that they move part or have to rest on each other, and one of your limbs gets in the way, that will not end well. And the hinge should be higher than I drew it. If you built a boat with a cabin, attach the hinge to the top, and limit rotation when outrigger hull and foil are to lee with water stays, rather than the beams I drew in Figure 15.

    Giles Whittaker worked out that if the rotation axis of the hinge is not parallel to the centreline, you can couple the pitch and yaw angle of the foil to heel angle. That offers some interesting possibilities, especially if you use a curved foil. I think the simplest boat that meets your requirements (as I understand them) would be a tacking outrigger with the outrigger hull on a rigid beam and its centre of buoyancy well forward of the centre of gravity of the boat. Then have a separate hinged Bruce foil about midships, with its rotation limited by a waterstay when to lee, and a hinge axis with the forward end further in and down relative to the rear. When the foil is to weather and the boat heels, that will make the foil pitch down and toe out. When the foil is to lee, the outrigger hull being far forward will pitch the bow up (if there is enough heeling moment) and increase the angle of attack of the foil that way.
     
  12. Owly
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    Owly Senior Member

    This is interesting stuff......... I looked at your AYRS article, and must admit that I'm still trying to get my head around it. There are some very interesting and innovative concepts there, the parallelogram setup, having an aerodynamic tail controlling the sail... which is something I've thought about also. That would seem to make sense for a ballestron rig like the Harry Proa series. The inherent self steering relative to the wind is an interesting concept I need to think about some more.

    I'm thinking that it makes more sense to have a strut with a foil extending to out to the leeward side than to try to use a foil on the windward side for balance. This would make it an upward lifting foil rather than a pulling down foil, and it could not pull out of the water. The problem of course is structure / weight. Merely a (shunting) trimaran without a hull on one side for practical purposes.
    Rob Denny's HP series are in my opinion the first really practical proas scalable to voyaging size, and I've followed his work for awhile. There is enough weight on the windward hull that they are reliably stable in virtually any conditions. A foil(s) would be of no little if any value here, as all they would do would be transfer weight to the leeward (long slender) hull...
    H.W.
     
  13. Florian
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    Florian New Member

  14. Robert Biegler
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    Robert Biegler Junior Member

    A shunting proa, being symmetrical fore and aft, has the centre of gravity midships. If you want your lifting foil at least a little ahead of that, to counter the pitch down moment from the rig's drive being higher than the water drag, you either need to move the foil, or deploy one and retrieve another, or you need tandem foils set up so that whichever foil is forward lifts more, and you accept the drag of the aft foil that is not doing much. I think then you soon end up not saving any structure, and a configuration like this might be a more efficient use of materials: Frog http://forums.sailinganarchy.com/index.php?/topic/197322-frog/

    Also, there is a lot of empirical work on foils that travel in one direction. The only work on bidirectional foils I know of is a set of simulations by Tom Speer.

    It all depends on what you want. If you like a tacking outrigger, and you want foil stabilisation that you don't need to control yourself, the hinged Bruce foil should be an interesting option. The moment you want foils to lift only, a tacking boat with bilateral symmetry seems more appropriate.
     

  15. Owly
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    Owly Senior Member

    I was thinking of a tacking proa or outrigger. Airfoils and hydrofoils are analogous, and do not work efficiently bidirectionally or for both upward and downward lift. Symmetrical foils do work, and are used on aircraft used for aerobatic (inverted) flight, but they do not work efficiently. The same would be true in water. You are just operating in a different Reynolds # range. ( R# is based on speed, fluid density, and chord). For bidirectional operation, I would want a flip over foil strut.... One foil in the air doing nothing, the other in the water.
    My point about the foil being to leeward is that it could not pop out of the water under the force of the wind against the rig, instead it would be driven deeper by a gust, or if by some incident it did pop out, the force would immediately drive it back under.

    On a tacking proa the longitudinal location would not change, and the ama on the opposite side could be made to fly on either tack. This would require a symmetrical foil, as it would be lifting on one tack and pulling down on the other. The ama could be quite small as it would have little function if the foil had sufficient authority.

    You could of course go a step further and have a simple sailing canoe with a strut and foil instead of an outrigger. Once you get moving, the foil does the stabilization. That might be kind of fun and exciting, and is not far off from some of the completely foil borne craft people have built. (only a single foil short of that).

    H.W.
     
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