My new 33 ft catamaran, design help

Discussion in 'Multihulls' started by tremendo, Nov 20, 2012.

  1. tremendo
    Joined: Nov 2012
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    Location: Nord of Venice Italy

    tremendo New Member

    Hello,
    I am a new member and I sketched this demountable catamaran.
    Like you can see the design of the hull is NOT my job, but I have a passion for catamarans and I'd like to build one completely as my characteristics
    LH= 9,94 mt
    LWL= 9,88 mt
    Beam of one hull= 1,5 mt
    BWL= 1,21 mt (probably too large)
    BH= 5,6 mt
    Displacement Lightship= 1,5 T
    max load =1 T
    I enclose drawing complete of sections and some 3D pictures

    I would like to receive comments and if possible suggestions to correct the mistakes
    Thanks
    Mirko
     

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    Last edited: Nov 22, 2012
  2. liki
    Joined: Nov 2008
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    liki Senior Member

    Like the idea, a separate boat for wife. Just include the possibility to separate them at sea. :)

    On a more serious side, how would you allow for moving between the hulls while underway?
     
  3. teamvmg
    Joined: May 2008
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    teamvmg Senior Member

    Where does the mast step?
     
  4. oldsailor7
    Joined: May 2008
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    oldsailor7 Senior Member

    The forward beam is too far forward.
    Yes, where do you mount the mast ?
    L/B ratio for hulls at 8/1 is max for a cruising Cat and too fat for a racing Cat.
    Hulls are a bit flat on the bottom, but otherwise looks pretty good. :D
     
  5. masalai
    Joined: Oct 2007
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    Location: cruising, Australia

    masalai masalai

    Been done - look at groper's build thread...
     
  6. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    I'm amazed how many people post renderings and ask:" What do you think?"
    It seems to me to be very, very difficult to assess a design without the numbers that go with it. Looks good.....
     
  7. oldsailor7
    Joined: May 2008
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    oldsailor7 Senior Member

    Doug.
    I got some numbers in the original post ---
     
  8. tremendo
    Joined: Nov 2012
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    Location: Nord of Venice Italy

    tremendo New Member

    Thanks for your comments,
    This is the first step of the project: the hulls, from some release, where they will be to my liking, I will think to design beams, floor and spar
    I attach the files 2D and 3D so you can see better.

    Liki, I am not able to design my wife, but the decision of a large hull is for the possibility to do something inside with a women, because now with my current cat I can only outside.

    Thanks Oldsailor7, yes I have seen too large the hull on the bottom, I will revise, I think also no more volume at bow, what do you think?
    My idea is a catamaran with a good volume inside the hulls for sleeping etc but fast, demountable for transport in a 13,6 mt lorry, rudders and foils pivot, for not problems in lagoon. Similar to my Brio cat but more comfortable and faster.

    I have seen groper's build thread, very interesting and compliments to Grober for the job, but is not the same idea
    I hope to receive further suggestions,
    Thanks
     

    Attached Files:

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

    Very quick thoughts

    You don't say, but I assume it is a sailing boat, not a powercat.

    Its not usually a good idea to have wide flat bottomed hulls for offshore sailing as they slam too much in waves.

    Drag is proportional to BWL, so reducing beam helps reduce drag

    If you fit a main crossbeam well forward you may not find there is enough hull to give it support. Also the longer the unsupported beam the bigger its section, and the necessary section size goes up quickly. And its a lot of weight forward which leads to more pitching.

    Don't just think about sailing. Also consider anchoring, coming alongside a dock, boarding from a dinghy (and then storing it on deck)

    It looks like you're going for wheel steering, otherwise where do you sit to steer? And how do you plan the rudders/tillers/tillerbar with a beam that far aft?

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  10. Petros
    Joined: Oct 2007
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    Petros Senior Member

    I like it. most comments above are good. Beams should be moved more to the center of the length, I would put more rocker in it and more volume up front as well. Slim bows are fast and sexy but when driven hard they are easy to bury and than pitch pole, a risk that racer may be willing to make, but not a good thing for a cruising cat.
     
  11. groper
    Joined: Jun 2011
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    groper Senior Member

    tremendo,

    As richard has already eluded to, wave making drag is proportional to the hull beam^2. So if you want this thing to be fast, you have to reduce the hull beam to well below 1200mm as you currently have it, personally i would not go above 750mm @ waterline for a 33ft sailing cruising cat... 40ft i would go upto 900mm max. My 35ft cat is only 640mm beam @ waterline, as i want it to be fuel efficient @ 20kts cruise speed all day long...

    One method i can see to do it is like the Shuttleworth designs with a double opposing flare and chine above the waterline... so you get small waterline beam, but with wide space above approx knee/waist level in the hull.
    [​IMG]
    [​IMG]

    i can see youve tried to fit the hulls in a container in your drawing? but how will you get them in there??? only way i can see is to use an open flat bed truck and use a crane to lift them onto it...
     
  12. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    John isn't the only one drawing boats with a big knuckle. I've been doing that for over 25 years. My Mustang is one boat that might suit you. I drew it as a sketch design about five years ago to accompany an article on performance cruisers.

    It has a similar hull shape to my Eclipse, which had double bunks in the hulls as well as a narrow WL beam, thanks to the flare. The flare has other advantages as well, which I mention in my article and on my website.

    It fits in a long/high non-standard container. Even so unless you have a two piece mast the container length will limit mast length

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     

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  13. tremendo
    Joined: Nov 2012
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    tremendo New Member

    Thanks for your suggestions,

    is a sailing cat, I attach some further rendering pictures, so you could have a better idea about hulls (please for now consider only the hulls) symmetrical 1 mould for both

    The central beam is missing on the drawing, I will do it bigger in composite, The rudders will be by stick with a sealing place like in my current cat, same idea but bigger, and faster (I hope)

    Sorry, I would like to post some pictures but I finish the space (Now how I can do to post it?? I don’t want to delete the old)

    See the video on my Brio Cat 7,6 mt
    https://www.youtube.com/watch?v=lvhkSvxkWIw&feature=g-crec-u
    https://www.youtube.com/watch?v=UZ83sfLfO0o&feature=g-crec-u

    I am enjoying it and I would like to do a bigger cat , similar my friend's cat, fast but less washing machine ( see the video below) we was sailing close to 20 knots
    https://www.youtube.com/watch?NR=1&v=y9WqvubbT_A&feature=endscreen
     
  14. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    The hull shape you sketched will be a real washing machine I'm afraid. Even a small knuckle will make a big difference. As will just flaring the hull. It isn't necessary to have lots of spray when sailing fast (check out the Saturn, Skua and Javelin videos on my youtube channel)

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     

  15. El_Guero

    El_Guero Previous Member

    I love the layout on your mustang. That layout makes me think you put some effort into your designs.

    And wasn't there someone asking about a containerable cat not long ago?

    Wayne
     
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