Formula for Boat Length Vs Beam

Discussion in 'Boatbuilding' started by Captain Pugwash, Sep 24, 2007.

  1. Captain Pugwash
    Joined: Sep 2007
    Posts: 1
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    Location: West Yorkshire, England

    Captain Pugwash New Member

    Hi.

    I know there is not going to be an exact answer here, but I'm looking for a general guide for how the length of a boat affects it's beam.

    For example, if you have a 12 metre motoryacht, then what would be it's likely approximate beam. If you had a 14 metre motoryacht, is there a general formula that would support what it's beam would have increased by - and so on.

    Is it linea, or does the ratio/formula alter as you move towards 20m+ boats, etc.

    I am looking for the general ratio/formula for both sailboats and motoryachts.

    Can anyone help?

    Thankyou

    CP.
     
  2. Raggi_Thor
    Joined: Jan 2004
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    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

    It's not possible to find a simple formula.
    You can try to collect data from boats you like and put them in a spreadsheet. Then if you plot beam vs length you will see the dots are spread around a curve, maybe. Short boats have relative more beam than long boats. L=2.5 x B for a small dingy for example.

    It's more like this:
    You want a boat of a certain size to carry something, or you want so many bathrooms etc, then you find you need a certain length and beam, then you estimate weight, and if you want a specific speed you estimate power, add more weight for the engine(s) and fuels and start again.

    For a given length, displacement, speed and power there may be an ideal beam, but most boats are compromises as you know :)
     
  3. Raggi_Thor
    Joined: Jan 2004
    Posts: 2,457
    Likes: 64, Points: 0, Legacy Rep: 711
    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

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