stabilizing a scow with foils

Discussion in 'Sailboats' started by josvos, Sep 7, 2014.

  1. josvos
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    josvos New Member

    Boat design is in a revolution these days. 2 revolutions actually: racing scows and foiling.
    How come they have not been brought together yet?

    It seems obvious in a way:
    A scow is wide, which is a good property for having foils.
    A scow sails best under a certain angle, as long is it is not planing. The windward foil would take the windward side of the boat up until the foil is out of the water. At this moment, it looses lift and the boat will have a stable heeling angle.

    It is a simple principle, and basically this should be enough to make an easy to sail, voluminous and fast boat.

    Some extra thoughts :
    1. It will need ballast. If the ballast is split in two, it can be on the tip of the daggerboards. By physical law, the center of gravity of two identical masses is halfway the 2 locations, so it would have the same effect as 1 central keel.
    2. The two ballasts would be at the same depth as the foils, i.e. where the tip of the daggerboard evolves in the horizontal foil, so the windward ballast would start to fly at the same time as the foil. The ballast is heavier as soon as it comes out of the water, so extra stability is achieved.
    3. The leeward foil is just lift. More speed, earlier planing. True foiling could be aimed at in a race version, but is not necessarily part of the setup.
    4. The race version would probably also not have ballast and only be suitable for inshore races.
    5. Dimensions for an exemplary boat could be 7m length, 3,5m width, daggerboards 80 cm deep. As such, the windward foil comes out of the water at 15° to 20°, a good angle for a scow.

    To be clearer, 2 pictures are added. Please do not focus on the optimist-style esthetics of the boat, it is just for explanation purposes.

    It seems obvious, but probably isn't. Please shoot at this concept, preferably at the principles of the behavior of the boat. Assume inshore sailing.
     

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  2. JSL
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    JSL Senior Member

    Check out Alexander Graham Bell (Scottish/Canadian) - he did a (powered) barge type hull with ladder type foils about 100 years ago. Held the speed record for several years.
    As to sail power.... just getting foil borne is the challenge
    ps
    (You need foils at each end, and each side)
     
  3. Doug Lord
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    Doug Lord Flight Ready

    If you're talking about a fast inlandlakes-type scow you're right on target. Tom Speer once said some place on these forums words to the effect that there would be a lot to gain with foils on a scow-at least that's how I remember it!
    This is a rough sketch of a tunnel hull scow using a curved lifting foil. I considered this several years ago and I might do the foil a bit different now.
    The rough sketch on the right is my thinking today for a scow foil. It would retract against the hull if desired. The shape is inspired by the TNZ foil used in the 34th AC and would have built in altitude control, whereas the curved foil would not. It could be a bit shorter as well.
     

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  4. josvos
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    josvos New Member

    @ Doug
    Thanks for your reply. I am not suggesting though that a scow with foils is innovative. That is an obvious match, certainly for racing purposes.
    I am mostly interested in your (and others) idea about the windward foil which fixes the heeling angle. In your drawing of the tunnel hull scow, add also the windward foil and then the story starts to be interesting.
    It will bring the boat on its leeward side in very light winds already. And the heeling angle will be very stable in all winds, since the lift of the windward foil stops as soon as the foil reaches the surface.
    With daggerboards with adjustable heigt, one could also define the heeling angle by retracting the windward one. That would be done in case planing is possible.

    @ JSL:
    Thanks for you reply, too. The concept is not about getting foil born, though. I want to know what happens before you get foil born. That is why it has no foils on the rudder.

    Also, the concept is not about designing the fastest boat; it would rather be used for cruisers. The windward foil would not add extra heeling moment anyway. Only, it would make scows more attractive for general (=recreational) purposes. And, to my feeling: scows are the future.
     
  5. daiquiri
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    daiquiri Engineering and Design

    Drop these two. It doesn't need a ballast at all. Foiling is very weight-sensitive, so you need a boat as light as possible. Hence, no ballast other than the crew.

    By the way - strictly speaking, the second point is true. But it is not very relevant nor important from the practical point of view. Talking about roughly 1-2% difference in the value of righting moment when you take into account the buoyancy of the lead ballast, the difference which can be more than compensated by weather and sea conditions and by the boat handling ability of the crew.

    Cheers
     
  6. CT 249
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    CT 249 Senior Member

    In what way are scows suddenly a revolution, when they have been around for about 120 years?

    Yes, in the Minis they have done well, but will they perform as well in classes that don't have the Mini's very large rig? And what will overcome the slamming problem in chop?

    My first boat was a scow Moth and for dinghies I agree that the concept is under-rated, but I'm still dubious about them being a better all-round concept for yachts.
     
  7. sharpii2
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    sharpii2 Senior Member

    I think a more interesting use for side mounted lifting foils would be to place them on a beam equal to the Beam of a boat with a very sharp bow, and have that beam quite far forward.

    The foils could effectively do the same job the wide bow underwater surface of the scow does in creating a lifting surface. This could eliminate one of the worse vices of a hull with an arrow head plan form. That is the bow digging in deep, as the boat heels, causing sometimes severe steering problems.

    Since this is mainly a problem when the boat is hard pressed under sail, the foils could be scaled to provide the adequate amount of lift only in strong winds.

    If this system could be made to work, the arrow head plan form hull would retain its main wave splitting advantage while losing its major vice.

    Just a thought.
     
  8. Doug Lord
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    Doug Lord Flight Ready

    Josvos post(s) were a year ahead of the birth of the first foiling (keelboat) scow-the Quant 23 designed by Hugh Welbourn. I just saw this thread and thought it should be updated with the revolutionary Quant 23. Not only does the boat foil in light air with a ballast keel but because the foils stick out to leeward they provide enormous extra righting moment for the boat w/o necessitating a windward foil that pulls down.
    Quant 23 Foiler Scow https://www.boatdesign.net/threads/quant-23-foiler-scow.53468/


    Quant 23 flying.jpg

    Quant 23 no credit3.jpg
     
  9. CT249
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    CT249 Senior Member

    Doug, any news on why they stopped production of the 23?
     
  10. Doug Lord
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    Doug Lord Flight Ready

    According to Michi, they have NOT stopped production on the 23........
     

  11. CT249
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    CT249 Senior Member

    Depends on definition, I suppose. The Quant website says "For the time being we are building only on order". Maybe I should have said "why have they stopped production of stock boats" or "spec boats".

    The Skeeta looks good and could have better performance than the UFO in displacement mode, although it's also a lot more expensive.
     
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