Catamaran resizing

Discussion in 'Multihulls' started by Muttley, Jan 27, 2013.

  1. Muttley
    Joined: Jan 2013
    Posts: 6
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    Location: Brasil

    Muttley Junior Member

    I am planing to build this catamaran , but I want to resize the boat in 30% , in order to gain some load carrying ability to go camping in some islands (I weight 80kg but my friends are ~ 100kg), and improving performance when sailing solo (I think would be possible to right it in case of a capsize, with some easy-right method with a paddler). I find interesting the cabin of this plan maybe to incorporate after, a self bailing cabin. And would be good to bring a 2-4 hp outboard depending on the ocasion.
    About the resizing, it will be done proportionally to all dimensions of the boat, even the plywood and wood thickness, besides the beam going to 3,6 meters(if proportionally, it will go from 2,41m (original) to 3,13 , a difference of 47 cm) .And because of the stretched beam,is it sufficient to reinforce its fittings? But when demounted on trailer, no more than 2,6 meter, but preferably very less. About the sails, I want to resize maybe 40% of the area but with Wharram Wingsail Rig, see Or could be more given the beam was stretched 50 %? But I don't want to raise the capsizing and pitchpoling ability, relying more on the larger beam.
    I don´t understand the method of the hull making, the Glen´s site says sheet plywood planking in continuous curve from keel to deck,I thinked it was stressed ply. with one builder doing wood planking:
    What do you think about it?

    My background: I never build a boat, only some scale balsa gliders.Have done Aircraft Mechanic course and helped my father to do some wood furniture when I was younger.
  2. catsketcher
    Joined: Mar 2006
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    Location: Australia

    catsketcher Senior Member


    There is a thing in design called the square cube rule. Things get 8 times more load (weight) if you double all dimensions so you can't simply scale a cat in many dimensions. You can usually make the hulls longer with no issue.

    I would suggest you go to a designer like Richard Woods or Wharram and tell him what you want and he will sell you a set of plans for a boat that is designed right from the start to do what you want. There is SO much work in building a boat it NEVER makes sense not to get really good plans to build from unless you have built a few first. Good plans will always pay back their cost many times in materials and time saved and extra resale value.


    1 person likes this.
  3. warwick
    Joined: Jan 2012
    Posts: 423
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    Location: papakura south auckland new zealand

    warwick Senior Member

    Would it not be easier to start out at the size you want from the start rather than scaling up one near the size you want.

    Are you intending to use the same designer? or some one else.
  4. Muttley
    Joined: Jan 2013
    Posts: 6
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    Location: Brasil

    Muttley Junior Member

    I Want a fast 21 ft catamaran, with dagger boards, with good performance upwind, lightweight and easy to build, and do not capsize so easy, and if needed could carry 5 people.

  5. Richard Woods
    Joined: Jun 2006
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    Location: Back full time in the UK

    Richard Woods Woods Designs

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