Designing a small monohull to cope with waves

Discussion in 'Boat Design' started by tlouth7, Aug 24, 2021.

  1. tlouth7
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    tlouth7 Senior Member

    Let's say you were given the task of designing a conventional, sloop rigged, monohull keelboat/yacht with the specific aim of going well to windward in waves. You are limited to 2T displacement and 2m draft, but everything else is up to you.

    What sort of hull shape would you immediately think of?
     
  2. gonzo
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    gonzo Senior Member

    Waves of what height and period?
     
  3. tlouth7
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    tlouth7 Senior Member

    Any you like. I guess I am mostly thinking of normal chop, not ocean swells.
     
  4. Dolfiman
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    Dolfiman Senior Member

    Another question is the crew number : 1,2, ... or 8 on the windward line ?

    Conventional mean you don't authorise water ballast ?
     
  5. tlouth7
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    tlouth7 Senior Member

    I think we rule out water ballast or canting keel, number of crew is up to you.
     
  6. gonzo
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    gonzo Senior Member

    You need to limit the parameters. What you are asking is known as optimization. Even though the holy grail is to design something that works great in all conditions, sadly the universe does not operate like that. There is no thing as a "normal chop". The only way to have a meaningful discussion is to quantify the range of amplitude and period. Also, define the wind speed, shifts, etc. for those weather conditions.
     
  7. tlouth7
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    tlouth7 Senior Member

    I'm not looking for an optimisation, just a discussion.

    For example it seems to me that there might be an advantage to limiting beam as this would reduce the amount that the boat is stopped by each wave, but then that also limits the righting moment available and so the power that is needed to push over the waves.
     
  8. gonzo
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    gonzo Senior Member

    A foiler with trapeze for the crew will probably have the least effect from the waves.
     
  9. Manfred.pech
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    Manfred.pech Senior Member

  10. jehardiman
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    jehardiman Senior Member

    Without a better SOR, the question is, as Gonzo said, undefined. 2 tonnes is not that much and the term "well to windward in waves" is fraught with issues. The two main items left unsaid are habitability and sea kindliness. Let us take San Francisco Bay and environs as an example. What I would design for an inside the bay sport dayboat would be very different from a single/double handed Farallon's boat. There are lots of old MORA and 1/4 toners that meet your requirements while being much more sea kindly than being beat to death on a trap or the risks of a foiler.
     
  11. Dolfiman
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    Dolfiman Senior Member

    The theme is very interesting because no longer adressed at such by the market, the current trend being at first the search of reaching/downwind speed in the planing mode combined with more beam for more accomodation. The promotion videos no longer showed the boat upwind on waves but downwind with a huge asymetric spi on a telesopic bowsprit, although the average sailor in coastal waters should do twice more hours of upwind than of downwind. Not to mention that some old school sailors prefers the feeling of a fine sailing upwind than a rush fast and furious downwind.

    In line with the previous comments, we need more specifications and constraints (like mass units per m2 for the building of the hull, of the deck, % of mass dedicated to accomodation, etc…). The degree of freedom for the design (like length, beam, sail area, ballast ratio) should be in dependence to each other through such spec. and constraints. For example, if you put more kg in the length, you should put less kg in the beam or in the ballast. Then, in such defined context, we can effectively discussed of the hull shape itself, in relation with the need of power (the RM at heel), the wetted surface, the balance and the waterlines streamlining of the heeled hull, moments of inertia (of mass, of waterplane aera) in relation with pitching and for the bow part, the ability to cope with waves.
     
  12. Skyak
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    Skyak Senior Member

    Kenichi Horie comes to mind. After building his own sailboat and sailing from Japan to San Francisco for fun he designed what he wanted in a small ocean crossing sailboat -simple round bilge with a very deep keel and bulb. He also did a wave powered boat (below).
    [​IMG]
     

  13. Squidly-Diddly
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    Squidly-Diddly Senior Member

    San Francisco Bay is known for fairly strong winds and lots of chop, and there are lots of fairly small sailboats that are locally designed for sport sailing on the bay. Look on Craigslist should give good idea.

    Then again there is how comfortable are you with getting how uncomfortable because higher displacement % full keel boat owners like to brag they stay out and just do a reef when all the new wonder-boats head for harbor when wind and chop kicks up.
     
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