Catamaran Hull Design

Discussion in 'Multihulls' started by redreuben, Sep 5, 2017.

  1. redreuben
    Joined: Jan 2009
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    redreuben redreuben

    I have a question about hull shapes at the waterline.
    It seems to be a given with modern hull shapes with fatter ends that the bow and stern should clear the waterline to minimise drag.
    Older designs like Wharrams, Hitchhikers and Horstmans don't, is this why they are double ended ?
    My lot seems to be a boat no longer than 8m, therefore to carry a payload and have some reasonable cabin height I'm going to have to have a deeper hull form, will this need to be double ended to minimise drag and how do you control pitching with such a shape ?
    Informed comment appreciated.
    The boat will be used long term to coast hop to Asia hopefully.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    What do you mean by the bow "clearing the waterline" ?
     
  3. redreuben
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    redreuben redreuben

    Bottom of the bow siting at or above the waterline rather than having any draft
     
  4. redreuben
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    redreuben redreuben

    I'm more interested with the transom.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    I thought that was what you meant, but just checking !
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Nope...just fashion and/or marketing!
     
  7. Richard Woods
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    Richard Woods Woods Designs

    Remember a hull is a 3D shape so you cannot take any one curve in isolation. A deep V hull has a very different rocker to a hard chine hull, yet both maybe equally efficient in flat water and at speed. In light winds and in rough water it may well be different of course. Which is the next point, you have ot design for the expected sea state, not just for best speed/efficiency. And most boats (race boats excepted) are not just used when underway. Cruising boats are lived on at anchor, for example, when good transom steps are very useful. Ferries need to dock easily, powerboats need a bigger transom to physically fit the engine, even at rest thus ignoring any stern squat etc

    it is all a complicated subject and you cannot take any one factor in isolation. You have to consider the boat as a whole, and as Adhoc will say, you need to design to the specific SOR. Which may lead to different hull shapes than what you might expect

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
    dsigned likes this.

  8. redreuben
    Joined: Jan 2009
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    redreuben redreuben

    I found some good info in the hydrodynamics thread.
     
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