Design Question on powering

Discussion in 'Boat Design' started by Salmoneyes, Oct 4, 2018.

  1. Salmoneyes
    Joined: Sep 2018
    Posts: 89
    Likes: 1, Points: 8
    Location: Southern Oregon

    Salmoneyes Junior Member

    She is Bruce Roberts penned but strayed a bit. Keel was lengthened, the masts lowered with smaller sail plan, and she is too heavy.

    Hull was built with a technique I was unfamiliar with but common for commercial steel fishing boats in Sweden. Can be modded to be stronger and loose weight at the same time even if only a 100 pounds.

    I have access to help from Bruce but we are looking at many options to get her numbers to all jive, and I am trying not to have him redesign it multiple times.

    The entire propulsion system is one way I possibly can drop 900 to 1000 pounds.
     
  2. Salmoneyes
    Joined: Sep 2018
    Posts: 89
    Likes: 1, Points: 8
    Location: Southern Oregon

    Salmoneyes Junior Member

    the disp/length ratio came out to to 447 using tom doves calculator.

    I looked at the formulas and I am working it out on my own, but I am teaching myself the math as I go, so it is a very slow process. When I start getting a headache I go work on the boat demo..
    Unfortunately, im running out of things I can do without having a master plan which Im making, thanks to help from this forum...
     
  3. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    Ive no idea what/who Tom Doves calculator is.

    It is a very simple calculation.

    The waterline length - in metres
    The displacement - tonnes

    The LD ratio is thus: Length / (displacement)^1/3

    That's it.
     
  4. Salmoneyes
    Joined: Sep 2018
    Posts: 89
    Likes: 1, Points: 8
    Location: Southern Oregon

    Salmoneyes Junior Member

    Sorry, I was referring to Gerrs formulas found in the Prop Handbook... There was more to that book then I thought originally.
     

  5. JSL
    Joined: Nov 2012
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    Location: Delta BC

    JSL Senior Member

    Displacement Length ratio in imperial is:
    D/(0.01 x LWL)^3
    D = long tons (2240#)
    LWL = feet
    as noted in Gerr's book pg 13, and also several other books.
    With your Disp/LWL ratio of 440+ you might expect a top speed of around 6.5 knots under power.
     
    Last edited: Oct 29, 2018
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