Will it plane?

Discussion in 'Multihulls' started by F3M4, May 3, 2011.

  1. F3M4
    Joined: Apr 2010
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    F3M4 Junior Member

    I'm attempting to design a catamaran used for inshore fishing. I'm pretty sure i've got the right idea, but wanted to double check with some more knowledgeable people. The boat will be a center console with an outboard motor powering it. The boat length will be roughly 16ft long and 7.5ft wide.

    [​IMG]

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  2. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    Most flat bottomed vessels will plane with enough power

    So I think the real question to ask is "Will it plane efficiently"

    Answer probably no

    I think you don't have enough buoyancy aft and by implication also have too much rocker. Also your hulls seem quite wide, or put it another way, your boat seems heavy

    Have you seen my Skoota 20 powercat design?? Seen on my website. Maybe something like what you are planning

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  3. F3M4
    Joined: Apr 2010
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    F3M4 Junior Member

    Richard, I have looked at your skoota design, but unfortunately it doesn't quite fit my bill.

    I am hoping to be able to reach higher speeds, as the areas in which we will be fishing require a fairly long run. The cabin design also doesn't afford much usability to the fishing aspect.


    I gathered from your post that the hulls would benefit from being more slender. I am wondering how much this will affect my draft.....

    I don't need a ridiculously low draft, but it certainly would be beneficial to my fishing efforts.


    I will revise my "design" and post another version up.
     
  4. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    Power Cat

    One thing you could do, besides studying Richards excellent work, is to look closely at existing power cats that meet your requirements-maybe Glacier Bay
    or other similar boats might provide you with a starting point. You would, in all likelyhood, save money in the long run by engaging someone like Richard Woods or another experienced power multihull designer to put together a design specifically tailored to your requirements.
     
  5. F3M4
    Joined: Apr 2010
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    F3M4 Junior Member

    The glacier bay 2265 is nearly exactly what I am looking for. My only concerns are the draft(17") and the length is a bit more than I want. I also want to stick to one outboard.

    In the end I may certainly wind up working with someone like Richard, but I am a stubborn engineering student with the tools and free time to attempt my hand at designing the vessel.

    I'm going up to 20' in length, as I see no reason not to. I'm also going to forfeit my low draft in lieu of more speed/wave handling.
     
  6. F3M4
    Joined: Apr 2010
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    F3M4 Junior Member

    Here's what I've come up with, it's amusing how different from my first attempt these are.


    [​IMG]
    [​IMG]
    Should I incorporate a small flat part to the bottom?

    And I forgot to thank you guys for the advice. I really appreciate it.
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I would strongly recommend you buy a set of plans. The questions you raise suggest you haven't the necessary grasp, in the fundamentals of yacht design. At least not enough to develop up this cat. This isn't a personal dig at you, just an observation based on your drawings and questions thus far.
     
  8. F3M4
    Joined: Apr 2010
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    F3M4 Junior Member

    I mean, I understand the concern, but the problem is that I can't find any appealing plans that suit my needs....

    No one has designs for a power cat around the 20' range that fits my description.

    Unless, of course, I'm missing them?
     
  9. Frosty

    Frosty Previous Member

    I think your design could be improved on.

    To me they remind me of a frog in an ice cube.

    sorry --I could'nt resist it
     
  10. DaveJ
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    DaveJ Senior Member

    1 person likes this.
  11. F3M4
    Joined: Apr 2010
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    Location: Baton Rouge, LA

    F3M4 Junior Member

  12. F3M4
    Joined: Apr 2010
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    Location: Baton Rouge, LA

    F3M4 Junior Member

    The name frosty must be describing your heart

    :)
     
  13. Spiv
    Joined: Jun 2007
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    Spiv Ancient Mariner

    I owned several power cats of different sizes and shapes, so what I discovered might be of help:
    • cut the drag by having nearly flat transoms, just a little V is OK.
    • transom trailing edge to be sharp (to loose the wave and get planing)
    • don't have any rocker, actually planing boats might even benefit by sinking the transom a bit (just the last metre and just a little, this will help keep the bows down and help the ride).
    • keep your stems vertical
    • have a wave-breaker in the tunnel and no flat surfaces, the Mantacat was the best cat I had. Se picture of a Mantacat tunnel.
    • have asymmetric chines (planing strakes) so the boat will react gently when hitting waves. What I mean is the outer and inner chines should be staggered.
    • you will need an XXL outboard shaft, I suggest a Yamaha. You might have to design a little pod in the middle of your tunnel so that the cavitation plate is just below water when planing, but check that you don't drown the engine when not planing.
    Hope it helps.
     

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  14. Doug Lord
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    Doug Lord Flight Ready

    ----------------
    Very interesting info, Stefano-thanks! I'm wondering why the asymmetrical planing strakes seem to make a difference. Did you try them symmetrical first or were they studied by the original designer? Intriguing....
     

  15. F3M4
    Joined: Apr 2010
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    Location: Baton Rouge, LA

    F3M4 Junior Member

    Thank you, this is exactly what I'm looking for.
     
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