Anti-bow wave foil?

Discussion in 'Hydrodynamics and Aerodynamics' started by misanthropicexplore, Apr 15, 2018.

  1. misanthropicexplore
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    misanthropicexplore Junior Member

    "...a square cross section would actually be superior to the typical v shaped hull. In addition he added a foil on the front of the hulls to eliminate the bow wave even at low speeds. He performed hull testing on his own, and at the MIT towing tank, and the results verified that these principles were valid..."

    That quote is from here: Building a Lifelong Dream https://www.maritime-executive.com/article/Building-a-Lifelong-Dream-2014-09-12

    Now, I am aware that a semicircular hull is the most efficient for a given displacement, but a rectangular profile is best for a given length, so the first part of that statement is not strange to me. But the second part, of using a anti-bow wave foil is new to me. I imagine this would work something like a bulbous bow, but tunable for various speeds under sail? Unfortunately I don't know. It's not in the original patent US5134950A - Sailboat - Google Patents https://patents.google.com/patent/US5134950, and my google fu is not helping me here.

    Can anyone bring some light to bear on this?
     
  2. gonzo
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    gonzo Senior Member

    Why do you thing a rectangular section is better than semi-circular. It has more wetted area, and less length for the same beam.
     
  3. misanthropicexplore
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    misanthropicexplore Junior Member

    Honestly I have no idea where I read that, I'll see if I can find the reference, but I have a very slow connection atm. I think the context was that if you are stuck with a certain beam and length, then a rectangular profile has a lower wetted area per unit of displacement than semi-circular, because it's shallower? But I see if I can find it. Or maybe that's always wrong...in case I have two questions about what that quote is talking about instead of one. Any idea what they talking about with that bow wave reducing bow foil?
     
  4. baeckmo
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    baeckmo Hydrodynamics

    Actually, a bow wave may be supressed by a foil. Like a bulb, it can be designed to create a "mirror wave", that has the effect of more or less cancelling the normal wave at the bow. As for the rest of the story you linked to; I didn't fancy wading through all the nonsense, so no further comments on the hull shape.
     
  5. misanthropicexplore
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    misanthropicexplore Junior Member

    http://www.multihulldynamics.com/news_article.asp?articleID=80

    From that site:

    " Notice that the Sharpie (rectangular) hull shape offers the lowest wetted surface! The geometric truth about the semicircle having the lowest wetted perimeter is no longer valid because the waterline beam was fixed to achieve a given length to beam ratio for the hull. If a designer fixes displacement, waterline beam and draft, the hull shape that gives the most displacement is the rectangular one. The semi-circular shape (Round in the figure) has to have a rectangular block added to it to get the given displacement while holding the beam fixed. Similar adjustments have to be made to the other shapes. Without these adjustments, the shapes may give less wetted surface, but will not give the chosen displacement and hull length to beam ratio. So the contention that the Sharpie hull shape offers the lowest wetted surface is correct under a very strict set of constraints. Otherwise, geometric truths still hold."
     
  6. misanthropicexplore
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    misanthropicexplore Junior Member

    Well it was written weirdly, and many would consider it an ugly hull. However, MIT really did patent it like he said. I'm trying to understand what validity they saw it that I (and you) do not. Bow wave suppression via foil is new to me. Do you know of any papers/sites that might have more on the subject? (I'm assuming since I don't see them everywhere that bulbous bows are better when the hull is motor driven, and that there are more faster per lb or per dollar methods dealing with wave resistance in sailboats.)
     

  7. David J Ritchie
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    David J Ritchie Junior Member

    Is there a diagram for how the wave cancelation foil is configured?

    I'm having trouble picturing it

    also

    That wave amplitude cancelation effect is also described in a theoretical paper, i read a wile ago, called the super-catamaran. I believe the demi-hulls were to be designed and spaced so that all wave pounding would produce its phase conjugate waveform. Simply put wave pounding knocks the bow up and the stern down, that downward force in the specially shaped stern acts as a wave maker (like at the pool) and the hull acts as a lever producing an equal size trough (downward dip) wave that the original chop wave falls into wile the boat passes harmlessly over it. This is off the top of my head sorry no link.
     
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