45' Cruising Catamaran Project

Discussion in 'Boat Design' started by sailhawaii, Oct 9, 2016.

  1. sailhawaii
    Joined: May 2016
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    sailhawaii Junior Member

    [​IMG]
    I started designing up a catamaran for fun, but it is starting to turn out kinda cool, so I'm starting to seriously consider building it, although I'm far from being done with the design. I've been lurking on the forum for a long time and trying to learn all I can and read all the books I can etc.

    Any feedback I could get on the design would be great. Although I've considered as much of the technical aspects that I know about, I still consider the design in the artistic phase. I've done the drawing in Rhino, the size and displacement should be close, but I need to figure out what I should do next for optimizing the underwater shape, mast position and balance. Where should I start?

    I was toying with the idea of maybe making it an open source or creative commons project. thoughts? anyone interested in contributing.

    BTW, the boat is 100% flat panel construction.

    More pictures can be found on http://www.sailhawaii.us
    [​IMG]
     
  2. gonzo
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    gonzo Senior Member

    I'd say that in even moderate weather, you'll get green water over the deck with that bow shape.
     
  3. brian eiland
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    brian eiland Senior Member

    Nice looking design,....and I like the idea of the flat panel construction.

    Is your Rhino self taught?
     
  4. sailhawaii
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    sailhawaii Junior Member

    Yes self taught rhino, this is my first Rhino project, but I'm a software designer so software is easy for me.

    As for green water over the bow, Take a look at the bow shape, it didn't show it the other pictures. There is a ton of volume. The bows are not wave piercing and the underwater shape is flatish toward on the forward vee to giving it some lift. Do you think that is enough or I should have less slope toward the front? or ??
    thanks,
    Bryan

    showshape.jpg
     
  5. brian eiland
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    brian eiland Senior Member

    Solitary Island 12m Kit Project

    Are you familiar with this project that was being worked on by a group in Australia.? Too bad that they had to abandon the project and their website is now down, but I saved a PDF document on their project (attached)

    It makes use of Duflex flat panels that appear to be quite popular over in that part of the world. There is also a prefab 'shoe' in their kit (the underwater portion of each hull).
    http://www.cruisersforum.com/forums/f48/are-cats-made-from-duflex-panel-kits-strong-22948-12.html#post1276593

    I was working on a few modifications that would allow for an alternative sailing rig for their kit.
    http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-33.html#post508282
     

    Attached Files:

  6. sailhawaii
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    sailhawaii Junior Member

    Yes, I'm familiar with that boat. On facebook they posted the company assets forsale. It uses a larger(20' I believe) poly honeycomb core panels. Seems like a cool design, too bad they couldn't make it work as a business.

    The Schionning & Grainger designs use the 4'x8' duflex panels a lot. The spirited designs by craig schionning are similar but use a shoe like the solitary island.

    Northstar in South Africa is building some schionnings and they are building full size panels. The prebuild a lot of stuff into them like openings and recesses for taping to make finishing easier.

    My current thinking is to make full size panels like that. I'm also considering building flat panel molds.

    My first plan is to build a RC scale model. It might be fun to test the performance of different rigs, like your design.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    It is the first thing that comes to mind, for sure, especially stern quartering could be troublesome.
     
  8. sailhawaii
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    sailhawaii Junior Member

    Thanks for the advice. I raised the bow up 11 inches and made the stern narrower on the overhang.

    Compared to other 45' catamarans I've looked at it has fairly long bows. The bows tips are more than 5' off the water now. Do you think it's still going to be a major problem? Suggestions?

    stern1.jpg
    side1.jpg
     
  9. Alik
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    Alik Senior Member

    Advice: designing a cat for the first time, don't place transom step too low to WL. As You have little idea of actual weights and their distribution, the lower step might sink after launching. I saw this problem on some Schionning cats as well as they are designed optimistically light...
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    There aren't many reasons to have a drooping sheerline on a boat's bows, and probably none on a boat like this.
     
  11. Richard Woods
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    Richard Woods Woods Designs

    I agree with Alik.

    You must also consider how to get on-off the boat. You don't always anchor off and use a dinghy. Or Med moor

    As my wife always says "I don't do jumps" whereas I say "how will my mother get on board" when tied alongside

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  12. sailhawaii
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    sailhawaii Junior Member

    Great advice, Maybe when I build the boat, I'll weigh it when I get close before determining the actual location lower aft step location in the actual build. Also in the current plan I bumped it up a few more inches.
     
  13. sailhawaii
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    sailhawaii Junior Member

    Everything is a compromise and because I'm designing the boat for me and the plan will never be offered for sale, so a lot is personal preferences, but I don't want to do something stupid, so let me know if you think my logic is off base.

    My primary reason is aesthetics, which is a both subjective and a dumb reason compared to seaworthiness. To try to achieve both, If the freeboard is high mid ship, it's not the bow that droops, but the mid ship sheer that rises. The problem with that as Mr. Woods points out that boarding from the side will be difficult at dock. To help mediate that I'm changing it so the hull side is close to the the same height as the aft steps, so you could step off them sideways onto docks of various heights.


    The second is windage, as it seems to me the time I should be most concerned about aerodynamics is when the apparent wind is in the 30-45 degree off the bow, so I'm trying to make the boat aerodynamic at that angle.
     

  14. JasonCatt
    Joined: Sep 2016
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    JasonCatt Junior Member

    Very cool looking cat. I'm surprised no one has attempted an open commons approach before. Keep it up, I'm definitely keen to keep an eye on your progress.
    What building materials are you thinking?
     
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