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Thread: Hull shapes for small catamaran

  1. #1
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    Default Hull shapes for small catamaran

    Hello everyone!

    Beginner questions coming up! I am thinking about building my first boat. I am leaning towards a very small catamaran. I'm thinking about 10 - 12 feet, or 3 meters or so. To learn the building process and also to hopefully have some fun with it while planning the next (bigger) one . Anyway, since I don't know much about hull shapes and so on I am wondering how certain changes affects the performance, stability etc. I will post a couple of pictures to illustrate what I am wondering about.

    How will these different changes to the hull shape affect the performance of the hull? For my first build, speed is not very important at all, stability, ease-of-building, load-capacity is more important, and being cheap/fast to build.

    Any tips, tricks, experience, input is greatly appreciated.

    And by the way, I have never sailed before so this little tiny, (hopefully) sailing cat will be my learning vessel.

    I want a small sail to move it about, I love the crab sail style. I've heard asymmetrical hull will help keep it straight? Probably want a center-board, fairly high free-board, some loading capacity.

    It will be a ply/epoxy probably even though I really would prefer not to use epoxy.

    So, in the pictures, hull-shape A is the easiest to build, I'm guessing. But what would be the draw-backs trying to sail this shape? Are any of the others a better option?

    Thank you.

    /Joakim.

    IMG_20190804_091303.jpg
    IMG_20190804_091319.jpg
    Last edited by Joakimu; 08-04-2019 at 09:43 AM.

  2. #2
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    Default Re: Hull shapes for small catamaran

    Are you thinking of designing your own first boat to build, then learn to sail on?
    Hope for the best, but plan for the worst.

  3. #3
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    Default Re: Hull shapes for small catamaran

    Yes

  4. #4
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    Default Re: Hull shapes for small catamaran

    Find and study as many plans as you can
    https://www.woodenboatstore.com/prod...758ea399&_ss=r
    It really is quite difficult to build an ugly wooden boat.

    The power of the web: Anyone can post anything on the web
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  5. #5
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    Default Re: Hull shapes for small catamaran

    If you are a teenager and this is a summer play project, make a simple pair of slim boxes and see what happens. Learn from a progression of these as you observe improvements or wrong turns.

    If you are at all serious, build a boat from an established design that is fairly simple and still tickles your fancy and learn how boats work from that.

    Sad to say that your original plan will probably be as successful as 99.44% of the rest that start that way, which is not at all. Physics will not be fooled by good intentions.
    Tom L

  6. #6
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    Default Re: Hull shapes for small catamaran

    It sounds like you are planning to learn yacht design, boatbuilding and sailing all in one grand endeavour. Forgive me, please, for being pessimistic, but that sounds like an exercise in failure. You may well be one of the very, very few whom are able to succeed at such a task, but the odds are against you. With great respect for you and your ambitions, I strongly reccommend that you step back a bit and do things in an order that will have a greater chance of success. Build your first boat from proven plans. Learn to sail it. Then, after reading all you can about yacht design and combining that knowledge with what you have learned from building and sailing, you will be ready to apply those lessons learned to the design of your next boat. Take slow, careful steps and enjoy your successes.
    Hope for the best, but plan for the worst.

  7. #7
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    Default Re: Hull shapes for small catamaran

    2019: returning from being sidelined with medical probs, crossing fingers worst is over, still in "armchair enthusiast" mode for time being.

  8. #8
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    Default Re: Hull shapes for small catamaran

    Well you are getting good advice here but you may also find some inspiration in the Italian 'Diecipiedi' (10 feet) group. They sail basically anything that floats and is 3m long, including catamarans (and trimarans).

    http://www.diecipiedi.it/ns/flotta/catamarani.html

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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by Plyboy View Post

    Thanks Plyboy, that's very helpful!

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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by Clarkey View Post
    Well you are getting good advice here but you may also find some inspiration in the Italian 'Diecipiedi' (10 feet) group. They sail basically anything that floats and is 3m long, including catamarans (and trimarans).

    http://www.diecipiedi.it/ns/flotta/catamarani.html
    Thank you Clarkey! Great resource!

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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by Peerie Maa View Post
    Find and study as many plans as you can
    https://www.woodenboatstore.com/prod...758ea399&_ss=r
    Thanks for the link. I like Richard Woods designs.

  12. #12
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    Default Re: Hull shapes for small catamaran

    "If you think you are too small to make a difference, try sleeping with a mosquito"

    -Dalai Lama

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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by Art Haberland View Post

    Thank you. It looks great! But it's a little bit too big for now. I'm looking more in the 10' range for a start. And I haven't seen that from Richard or Wharram or Kohler really.

  14. #14
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    Default Re: Hull shapes for small catamaran

    At around 11', the Arafura Cadet is almost as small as you have in mind, and a very simple hull shape for home construction. One of the first boats I ever sailed, and good fun. https://arrowarafura.com/?page_id=1576
    Getting some experience on the water with established designs before having a go at designing a boat yourself is sensible advice. Consider it an opportunity to research design ideas!

  15. #15
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    Default Re: Hull shapes for small catamaran

    Why so short?

    Peace,
    Robert

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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by coucal View Post
    At around 11', the Arafura Cadet is almost as small as you have in mind, and a very simple hull shape for home construction. One of the first boats I ever sailed, and good fun. https://arrowarafura.com/?page_id=1576
    Getting some experience on the water with established designs before having a go at designing a boat yourself is sensible advice. Consider it an opportunity to research design ideas!

    Thank you coucal! Very interesting cat. I will have a good look at it. I appreciate the suggestion.

  17. #17
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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by amish rob View Post
    Why so short?

    Peace,
    Robert
    Hello Robert. For several reasons, but mainly because it's cheaper and faster to build and a good start I reckon.

  18. #18
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    Default Re: Hull shapes for small catamaran

    Interesting topic, though I think it would be wise to totally abandon the hope of such a small cat having anything close to good "load capacity". It's just not going to happen on such a small one. Even on a somewhat larger cat like a Hobie 14 if you wander over to the back corner of the trampoline that corner of the boat goes under water. A smaller boat is cheaper to build - unless you find that the finished product can't do what you thought it would be capable of and you don't have much use for it.

  19. #19
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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by Joakimu View Post
    Hello Robert. For several reasons, but mainly because it's cheaper and faster to build and a good start I reckon.
    It just seems pretty short for good performance from a catamaran. The beam would need to be so narrow, and the hulls so beamy, why not just build a pram?

    Anyway, good luck. And have fun.

    Peace,
    Robert

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    Default Re: Hull shapes for small catamaran

    For simple and cheap, you might be inspired by taking a look at the Bernard Kohler cataproa design --- see K designs. This is a boxy hull form, much like those shown in the OP and the rig is close to the crab claw sail mentioned as well.Maybe you could think of it without the cabin, but take note that only one daggerboard and a single rudder are a saving over duplication required on a conventional cat configuration.

  21. #21
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    Default Re: Hull shapes for small catamaran

    Another catamaran designed to be very quick and easy to build is James Wharram's Hitia 14. Wharram's boats can be built very inexpensively, too.

    -Dave

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    Default Re: Hull shapes for small catamaran

    Here's another idea. Back in the day I wanted to do something similar, though not a catamaran. I was pretty experienced as a woodworker and had tools. I took the Westlawn yacht design course and a boatbuilding course at Mystic Seaport taught by John Gardner. That, plus a library of 100+ books. That proved successful and I did design/build/restore quite a few boats. It just takes more effort than a few sketches on a legal pad.
    Everything changes . Everything is connected . Pay attention

  23. #23
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    Default Re: Hull shapes for small catamaran

    Going down a slightly different avenue
    Creationists aren't mad - they're possessed of demons.

  24. #24
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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by P.I. Stazzer-Newt View Post
    Going down a slightly different avenue
    Tarpaulin. Wonderful. We abbreviate, so.

    Peace,
    Robert

  25. #25
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    Default Re: Hull shapes for small catamaran

    #23 reminded me of this. 8 long sections...



    Peace,
    Robert

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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by Todd Bradshaw View Post
    Interesting topic, though I think it would be wise to totally abandon the hope of such a small cat having anything close to good "load capacity". It's just not going to happen on such a small one. Even on a somewhat larger cat like a Hobie 14 if you wander over to the back corner of the trampoline that corner of the boat goes under water. A smaller boat is cheaper to build - unless you find that the finished product can't do what you thought it would be capable of and you don't have much use for it.

    Thanks for sharing Todd. I appreciate it.

  27. #27
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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by amish rob View Post
    It just seems pretty short for good performance from a catamaran. The beam would need to be so narrow, and the hulls so beamy, why not just build a pram?

    Anyway, good luck. And have fun.

    Peace,
    Robert
    Thanks, I will . What is a pram? Is it a proa?

  28. #28
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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by Lugalong View Post
    For simple and cheap, you might be inspired by taking a look at the Bernard Kohler cataproa design --- see K designs. This is a boxy hull form, much like those shown in the OP and the rig is close to the crab claw sail mentioned as well.Maybe you could think of it without the cabin, but take note that only one daggerboard and a single rudder are a saving over duplication required on a conventional cat configuration.
    Hello Lugalong. Thank you. Yes, I have seen his designs and I know about the proa, but how difficult is it to sail a proa? I actually once bought the KD 860 plans from him.

  29. #29
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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by Woxbox View Post
    Another catamaran designed to be very quick and easy to build is James Wharram's Hitia 14. Wharram's boats can be built very inexpensively, too.

    Hello Dave. Thank you, it's a beautiful catamaran!

  30. #30
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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by WHYankee View Post
    Here's another idea. Back in the day I wanted to do something similar, though not a catamaran. I was pretty experienced as a woodworker and had tools. I took the Westlawn yacht design course and a boatbuilding course at Mystic Seaport taught by John Gardner. That, plus a library of 100+ books. That proved successful and I did design/build/restore quite a few boats. It just takes more effort than a few sketches on a legal pad.
    Thanks for sharing.

  31. #31
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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by P.I. Stazzer-Newt View Post
    Going down a slightly different avenue
    Very cool!

  32. #32
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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by Joakimu View Post
    Thanks, I will . What is a pram? Is it a proa?
    No.

    A proa is a multi hull that shunts.

    A pram is a monhull.

    If you really want a multihull, and space is limited, why not a Waapa, by Dierking? They come apart into sections, and are as simple as boatbuilding gets.
    You could learn a lot about building, and have a nice useable boat, to boot.

    Peace,
    Robert

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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by DeniseO30 View Post
    Hard questions:

    Why a catamaran?

    Where did you get the idea it is cheap/er to build a boat?

    Do you have sailing experience at all?

    Suggestion, you get some sailing experience, right after your first sailing experience the boat you want, rather than the boat you think you want to build will change everything you are thinking.
    I just love catamarans. That's the simple answer.

  34. #34
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    Default Re: Hull shapes for small catamaran

    Quote Originally Posted by amish rob View Post
    No.

    A proa is a multi hull that shunts.

    A pram is a monhull.

    If you really want a multihull, and space is limited, why not a Waapa, by Dierking? They come apart into sections, and are as simple as boatbuilding gets.
    You could learn a lot about building, and have a nice useable boat, to boot.

    Peace,
    Robert
    Thanks for the suggestion Robert. But, in the future I might want to build a bigger catamaran design so this is a sort of "trial", but also just fun.

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    Denise, Bristol PA, Oday30, Anchor Yacht Club, On tidal Delaware River. my current project; http://forum.woodenboat.com/showthre...0-Ducker-Resto

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