Mini 12 or scale down America cup

Discussion in 'Wooden Boat Building and Restoration' started by bilco, Jan 27, 2005.

  1. bilco
    Joined: Sep 2004
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    bilco Junior Member

    A group of my friends and I are looking at building 3 small keel boats (cold mold) to race on the Tamar river in Tasmania.
    We have a mixture of skills to get us through the project.
    But finding a design is proving very very hard.
    We were hopeing for a mini 12 or 2.4 mr looking boat ,but with a bulb keel.
    Can anyone offer any advice on where to get line drawings?
    Is it ok to scale down a large boat?
    We need a design that is great for racing.
  2. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Very rarely does a larger boat scale down well, particularly if the scaling factor will be big, as would be the case of a 12 meter down to a 2 meter. As a result of the changes made you'd likely have a 2 meter that doesn't look at all like the 12 you're trying to copy. Most of the 12 meter designs that you may be interested in will be under the protection of copyright and it would be illegal to copy it, even if the scale was changed.

    In a boat that size you just be able to fit your body, let alone counter balance a lofty AC rig. So, to answer your questions about scaling down as you hope. NO, it wouldn't be a wise idea, basically she'd just flop over on her side. If you scaled a 3 meter boat down you'd have a chance of success, but still would require a custom effort by a designer.

    There are thousands of small "sporty" craft designs available. Build one of those, rather then trying to invent a new class which you clearly aren't skilled enough to do yet. Do a search for keel boats and select a design very close to the size you need. Until you gain a great deal more experience, don't change the scale of the design, just build it and have fun.

    A used International 2.4 meter will run about 5000 euros, a well equipped one 6 to 7000 euros. You'll be hard pressed to build for that and it's a class boat so there will be locals you can race, besides your friends.
  4. I am missing something on this scaling plans up and down. I have had plans scaled up by 6.5 times in 1 pass, and the enlarged blue prints retained the proportions perfectly. Why was I, O K ?
  5. PAR
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    PAR Yacht Designer/Builder

    Richard, I don't think they want to decrease the size of the plans, but in fact the design itself. Lets take a look at L. F. Herreshoff's R-boat Yankee and try to scale her down. She's a little over 37' LOD has a 26' LWL, a beam of about 6'8" and around 9' of draft. Bring this down in scale to 12' LOD (approximately 3x reduction) her LWL is about 8'5", beam 2'3" and draws almost 3' of water. This makes a boat narrower then most canoes with a 3' draft. The same works in reverse, except you end up building a boat with way to much beam for her length. A 22' LOA, 20 LWL, 8' beam centerboard sailor scaled up 3 times would make a 66' LOA, 60' LWL, 24' beam centerboarder and clearly too fat a boat.
  6. I always forget to scale down the people and " Reynolds numbers and their brethern ". :p
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    There have been a few attempts to use scaling factors to straighten this out, but none work real well. In small increases and decreases, more then just changing the station spacing would permit, the conversion formulas seem to work okay, but when the ratio gets over a certain percentage it goes to hell pretty quickly.

    The International 2.4 is patterned after the AC boats and does have an AC style sheer, appendage profiles, bow and stern profiles worked into the design, but that's about as close as they can get in this scale. They do look pretty good on post cards (just like snow)

    It's what construction workers would call a 80 footer (woman walking 80' away) As she got within 70 feet you'd see what was really going on and get back to work . . .
  8. B. Hamm
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    B. Hamm Junior Member

    The Norlin is basically a one design and the most popular boat in the 2.4 meter class. But the class is really a developement class so there should be home built plans available. These boats though are not inexpensive to build for their size, they have relatively high weights and the rig is complicated, along with something like 400 lbs. of ballast.

    For the past few years I've been working on a very simple mini keel boat of around 12 ft. but designed for homebuilders. Unfortionately right now it's incomplete and the prototype never has been built, not yet anyway. This one would though be a bunch less expensive to build.

    Bill H.
  9. pathetic
    Joined: May 2005
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    pathetic New Member

    Hey i am looking for plans for a mini-12 or 2.4 mr for me and my dad to build if anyone could help me out tha would be great.

    Thanks matt
  10. yokebutt
    Joined: Aug 2004
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    yokebutt Boatbuilder

    Look a little bit up north, I know they designed at least one good 12 meter up there.

    Seriously, any decent yacht designer can provide you with a suitable shape.

  11. Tactic
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    Tactic Junior Member

    What about something like this?


    Attached Files:

  12. marshmat
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    marshmat Senior Member

    It'll be hard to find something race-ready in that size. Tactic's pic there looks about as good as you'll get. You need something that's designed from the outset to be this size. As everyone else has said, scaling a larger boat simply will not work. The CG, CB, metacentric height, centre of sail effort, etc. will all be different and the boat will not perform well at all. If you refine your search, you should find a few more designs like the one in post #11 above that will suit your needs.
  13. Tactic
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    Tactic Junior Member

    Thee are a few similar production boats avalible.I have searched and searched but have been unable to find plans for anything like this.So I designed my own.
    I am interested in taking the concpt further,The design i have shown can be built by a amatuer using various strip planking methods.
  14. byankee
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    byankee Junior Member

  15. RWL
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    RWL Junior Member

    There is a very active Mini 12 fleet in the Pacific Northwest, with about 40 or 50 boats between the Royal Victoria Yacht Club (Victoria Canada) and the Seattle Yacht Club. I believe the Seattle Yacht club has purchased a number of Victoria designed Mini 12s in the last year or two. They are being produced by John Booth (Booth Enterprises I think is the business name) in Victoria. They are called Deceptions. I would guess you could contact the Royal Victoria Yacht Club to find out who is the class representative this year.
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