Design Question on powering

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

  1. Salmoneyes
    Joined: Sep 2018
    Posts: 53
    Likes: 1, Points: 8
    Location: Southern Oregon

    Salmoneyes Junior Member

    I have been getting great information to resolve issues on our project here, so, I was hoping I could get a lesson in the engineering process for sizing a propulsion system for a full displacement hull.

    Specifically mine, as I am rebuilding the whole boat and should confirm that what we have is what we should have.

    Happy to fill in blanks if you need, but i'm getting better at my math so I could give the formulas a go first to avoid wasting your time.

    Thanks in Advance
     
  2. philSweet
    Joined: May 2008
    Posts: 2,103
    Likes: 111, Points: 63, Legacy Rep: 1082
    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Gerr's Propeller Handbook is a good place to begin. It's set up as a propulsion system cookbook.
     
  3. Salmoneyes
    Joined: Sep 2018
    Posts: 53
    Likes: 1, Points: 8
    Location: Southern Oregon

    Salmoneyes Junior Member

    Am I using "propulsion system" incorrectly if I am referring to engine, gear ratio, prop shaft diameter and prop size and pitch?

    I realize that they are all going to use different formulas but one works hand in hand with the other and should be matched..

    My concerns are that as I go along with my project, I am realizing that the builders used whatever was available at the time.

    For example, the plans called for up to 85HP and we have 130. The propshaft is 45mm and the screw is 23". All much bigger than commonly found on a 40 footer, however it is much heavier than the original design.

    Id like to understand the math so I can make informed decisions on my mod options rather than ask the designer to run hundreds of options for me. My brother-in-law is an engineering mathematics teacher and is always happy to help me, thank god...
     
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