Tacking Proa (for lack of a better term)

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

  1. Robert Biegler
    Joined: Jun 2017
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    Location: Trondheim

    Robert Biegler Junior Member

    At this point, I have trouble visualising what you have in mind. If you are still discussing a tacking outrigger, than sometimes the foil will be to lee and need to push up, sometimes to weather and need to pull down. If you always want a foil to lee, and you want to tack instead of shunt, you need a foil on either side. Then a catamaran or trimaran would seem most logical, or a triscaph, like the later incarnations of Loisiers 3000: . If you need the boat to go alongside somewhere, then the cat seems most practical.

    If you are willing to let the foil pull down on one tack, then you might be thinking of a foil adjusted by a mechanical sensor, like the wand on the Rave Windrider or the little waterski ahead of the foil as on the Hobie Trifoiler;

    There used to be a kit for that, the K-Wing Sailing System for kayaks. The only trace I can find of it now is one low resolution picture in a primer on kayak sailing: Kayarchy - sailing rigs for kayaks & canoes https://www.kayarchy.co.uk/html/01equipment/014sailingkayaks.htm The reviewer is unenthusiastic, but it is not clear whether that opinion is based on experience or theory.

    There was also the Blue Arrow challenger for the America's Cup that pretended to be a monohull by replacing the outer hulls with adjustable inverted T-foils: [​IMG]
     
  2. Owly
    Joined: Oct 2016
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    Location: Montana USA

    Owly Senior Member

    I didn't express myself very clearly..... This is purely a flight of fancy speculating on what one might do. It's probably pretty impractical to to build an outrigger on one side, and a foil on the other, but it would allow you to fly the outrigger on each tack using the foil with minimal risk of capsize. The Blue Arrow shown makes more sense, dispensing with the outriggers altogether.........but depending on foils completely, it would be pretty unstable unless it's moving all the time. I've personally zero interest in racing, but it's useful to be able to make speed at times.

    With an outrigger on one side and a foil on the other in a tacking proa, the foil would have to provide lift when it was on the lee side, and would be the only thing keeping the boat upright unless you were hiking out on the other side. You could allow (would want) the outrigger to fly. The foil could be automatically controlled by the attitude of the boat as sensed by a linkage with a pendulum weight. On the other tack, the outrigger would function like the outrigger on an Atlantic proa, but you could use the foil pull down on what is now the windward side, lifting the outrigger out of the water. The outrigger would be installed in such a way that at a level attitude it would be just clear of the water. The whole idea is to have the outrigger flying virtually all the time on both tacks, only being in the water at slow speeds and at rest. The outrigger is mainly "insurance" in case the foil pops out of the water when the foil is on the lee side. It also allows you to sail in thin water.....hiking out on one tack.
    The only reason for not having a foil on each side is drag. You'd probably want to pull up the windward foil.
    A simple gravity pendulum linkage might not do a good job for auto control. It might call for a gyro to do a good job.... another level of complexity. Imagine a small gyro operating a trim tab.. similar to how a wind vane steering system works but keeping the boat level... you would use the force of the water passing by to amplify the force of the gyro and control the foil. It could be controlled by hand....perhaps with a trim wheel. The faster you went, the less angle of attack would be needed. An interesting toy to play with.
    ** The water ski on the boat in the Utube is interesting.... it inherently wants to stay on the surface

    I'm wondering what you can do with foils to make them inherently stable at least with reference to the water surface. an angled foil projecting above the water surface could be made to maintain depth more or less when pulling providing lifting force. The deeper it goes, the more foil area is submerged, but that doesn't work the other way when you are pulling down.
    H.W.
     
  3. Robert Biegler
    Joined: Jun 2017
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    Location: Trondheim

    Robert Biegler Junior Member

    My guess is they needed a RIB to get Blue Arrow started up. Or you could make the hull just wide enough, and perhaps the foils just voluminous enough, that the boat doesn't fall over at rest. That seems to be the approach taken by Gerald Holtom when he designed Foiler 21 in the mid 70s
    [​IMG]

    Mounting them high enough that a few degrees of heel gets the windward foil out of the water solves that problem without moving parts.


    A pendulum would be sensitive not only to roll, but also changes in course. A gyroscope would try to keep the boat level, which is fine if the water is flat, but will cause trouble when it is not. I would prefer to follow the water surface.

    That waterski is one solution. The wand used to control a trailing edge flap in the Moth dinghy class, and the Windrider Rave is another:


    If you want to achieve the same without moving parts, and you know that your foil only has to provide lift, I know of three features you can use, singly or in combination:
    1) Increase lifting area as the foil is pushed down, either by inclining the foil (as you mentioned), or by mounting additional foils higher up (see ladderfoil).
    2) Let the tip of the foil be closer to vertical than the root. Then if some of the angle of attack comes from leeway, the more the foil comes put of the water, the larger a proportion of the total area is in the vertical(ish) tip, and the total force from the foil will be more horizontal. You can see that angled tip at 1:24 in this video of Hydroptere:
    3) Use washout on an inclined foil. Twist the foil so that angle of attack near the tip is less than near the root. Then lift increases even more as the foil is pushed down than it would from the increase of area alone.

    Look at the lower strut on the windward foil of Foiler 21. If you made that large enough and angled it appropriately, you could use that to prevent a foil from pulling down too deeply.

    Some of what you're thinking about is explained at greater length in the Amateur Yacht Research Society's October 1970 publication "Sailing Hydrofoils", available for free at Booklets – Amateur Yacht Research Society https://www.ayrs.org/booklets/ More up to date work is in Catalyst. Have a look at the index: Index to Catalyst Nos 1-19 – Amateur Yacht Research Society https://www.ayrs.org/catalysts/catalyst-index/
     
    bajansailor likes this.
  4. BobBill
    Joined: Oct 2009
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    BobBill Senior Member

    A boat (proa) is either a shunter or a tacker. Besides, each has its rationale, so who really cares?
     

  5. BobBill
    Joined: Oct 2009
    Posts: 781
    Likes: 14, Points: 18, Legacy Rep: 157
    Location: Minnesotan wakes up daily, in SE MN, a good start,

    BobBill Senior Member

    "Ninja" is now-defunct SA small tacker in a box. Slicker'n seagull poop, but no money to spread the rig.
     
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