Modifying hull beam

Discussion in 'Multihulls' started by redreuben, Apr 22, 2011.

  1. redreuben
    Joined: Jan 2009
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    redreuben redreuben

    When modifying a hull for a bit of extra length it is generally excepted that you simply space out the frames the required amount at each station.
    But what about beam ? If you wish to keep said hull at same proportions and gain some internal space for a double bunk or whatever.
    How would you go about this for a chined hull or a round bilge hull ?
    Only one assumption and that is that headroom and freeboard are adequate.
    Looking forward to the ideas,

    Cheers,
    RR
     
  2. MikeJohns
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    MikeJohns Senior Member

    You scale the lines accordingly. But be aware that scaling in any dimension should be run past the designer, it's easy to end up with inadequate scantlings, stability or performance if they were borderline to start with.
     
  3. Richard Woods
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    Richard Woods Woods Designs

    And you'll still want the bow to be pointed, so the first few stations may not scale the same as further aft

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  4. PAR
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    PAR Yacht Designer/Builder

    Add to the deadwood assembly's width. For example if you have a 3" wide keel, make it 6" with little worry, though things can get ugly fast if you need more then a few inches. As Richard mentioned you can "streamline" the widened portion of the hull, by adding, again down the centerline, but starting with zip at station 1, then progressively adding until midship, then decreasing until station 10. I will add, that making a boat very much fatter can dramatically affect the preformance, efficiency, maneuverability and most importantly structural global loading of the yacht. I'm not sure what you're attempting Redreuben, but unless you're talking about a few inches, great care should be exercised or a once fine design can easily become a pig.
     

  5. redreuben
    Joined: Jan 2009
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    redreuben redreuben

    Par, this is purely an academic question at this stage as you often read in these pages about stretching hulls, which is fine for larger boats where internal beam is adequate but in smaller boats increasing the beam proportionally would give more useable volume other than just waterline length. But what I am thinking is along the lines of taking a cat hull from 8.5 to 9m and increasing the beam proportionally not, just making a hull fatter, I am well aware of the hazards this presents.
    RR
     
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