A few questions from a 1st time Catamaran builder

Discussion in 'Boat Design' started by Greyhaven7, Oct 19, 2008.

  1. Greyhaven7
    Joined: Oct 2008
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Hampton, VA

    Greyhaven7 New Member

    Hello everyone! I'm trying to tackle one of my "life goals" of building a boat. I've been working on this project for the last two years doing research, drafting up design after design, even building scale balsa replicas of designs I've "finalized".

    I've settled on a 24' Cruising Catamaran (powered by a single center-rear mounted outboard and possibly sails as well) with the following basic specs:
    • LOA: 24'
    • Beam: 14'
    • Beam of each hull: 3'
    • Draft: ~1.5'
    I have sketched out, though, unfinished plans on paper (will be put into digital format soon) and technical numbers like prismatic coefficient and waterplane coefficient if anyone would like or needs them to answer my questions. I will also be making the *finalized* plans fully available (for free) to anyone who wants them.

    What I want out of this boat:
    • To go out on the James River and other waterways around Hampton Roads (****NOT THE BAY****) with friends to hang out... fish... whatever.
    • Space on the deck and inside the cabin and hulls (hence 24' up from 10' in my original design, though I'm still working on this as it is dependent on answers to some of my questions)
    • Initial Stability (hence I'm going with a catamaran and not a mono-hull)
    • Slick-looking, "yacht-like", modern design with "clean lines"
    • Inexpensive (hence I'm building it myself in my own backyard)
    • Structural integrity

    What I AM NOT specifically designing for or do not care about:
    • Speed
    • Rough weather/off shore capability (obviously it needs to be able to handle some weather but I'm not planning on going out in storms)

    OK, here are my questions (please keep in mind that I'm doing this for the first time):

    1. Is 12 inches enough vertical clearance from the waterline in the tunnel (under the main deck between the hulls)? I don't mind some clapping noises, but I don't want a situation where the boat could be damaged by waves slamming UP at the underside of the main deck. (Remember, I'm not going for any kind of high speeds here either.)

    2. How would I best design/build the "aka"s (or whatever you want to call the crossbeams that connect the two hulls). I'm thinking that using plywood, epoxying several sheets together to gain a thickness of 3 or 4 inches, to create three bulkhead+crossbeam+bulkhead units (each as one solid piece). Each of these would then have horizontal diagonal supports to stop them from torquing along the length of the boat (letting one hull get ahead of the other). This, or something very similar, seems like a common method that I've seen used in some larger cats. Thoughts?

    3. Are thick "home-grade" plywoods acceptable materials for building bulkheads and other components of the boat that will not directly touch the water? (I'm sort of expecting a "no" here.) If not, why, and do you have any suggestions on what woods are best for this purpose?

    4. Would cutting out the interior surface area of some bulkheads (not any of the crossbeam/bulkhead-combos) to make it so you could get through them, leaving 6" of bulkhead around the edges leave enough structural integrity?

    5. My current plan is for a bulkhead every 2' along the interior of the hulls but I'm considering increasing that to 3'. Does this seem reasonable or not?

    6. What thickness should I aim for on the hulls' skins? (using composite ply) Consider also that I need to make a 180ยบ "U-turn" around the bottom of the hulls in a 1.5' radius.

    If you've read all that, I sincerely thank you and would REALLY appreciate any thoughts or advice. I'm trying to plan out this entire thing before I even buy one sheet of plywood.
  2. rasorinc
    Joined: Nov 2007
    Posts: 1,854
    Likes: 71, Points: 48, Legacy Rep: 896
    Location: OREGON

    rasorinc Senior Member

    new cat build

    Hello, for some good info on building a cat go to glen-L marine designs and click on boat plans then click on outboards. The Wildcat is a 24' boat and you can go to customer photos and see a whole build out of this Cat. Being you will use it in saltwater you must use epoxy and bronze fasteners. This site and the builders forum within will inform you of many things you need to know. Stan
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