Newby questions on sailboat design

Discussion in 'Boat Design' started by Kent Multer, May 25, 2010.

  1. stubby
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    stubby Junior Member

    yeah, first I'm a kiwi and we (and aussies) spell different to you yanks :p
     
  2. stubby
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    stubby Junior Member

    Drawing a 30ft model up now, to have it 8ft wide and plenty of head room is a bit of a stretch, I would say maybe 10ft wide, I'm 5'8" and sail on a beneteau first 31.7, and that has just enough headroom for me, so it would be possible to get 6.5ft of headroom, but it would be hard, and with only a beam of 8ft, it will always have high windage and low stability, unless you have a MASSIVE lead slug on the bottom.
     
  3. Kent Multer
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    Kent Multer Junior Member

    "Interior edges," got it. Thanks, that did the trick for getting rid of the unwanted surfaces.

    8ft. wide seemed like a good starting point, and it's the standard size for plywood, so construction of an 8ft. hull could be a lot simpler than 9. Narrow boats need less sail/motor power than wide ones of the same displacement; and I think I've read of other advantages for them that I don't recall just now.

    I don't envision owning a trailer for this boat, or a truck that could pull it. If necessary, I'll hire someone to move it.

    I'm planning on using leeboards. I like the look; they're easy to build and maintain/repair; and they don't clutter up the interior. Fixed keels are out because I want shallow draft.

    Thanks again --
     
  4. stubby
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    stubby Junior Member

    I would alos consider a Steel Centerboard, it will give you good righting moment, and shouldn't be too hard to use or fit, the top of them can work perfectly for a step to the cabin, or even a table to sit around. not only that but it will give you MUCH better performance.
     
  5. stubby
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    stubby Junior Member

    What about something more like this? It has a draft of approx 1ft, it has plenty of headroom, 11ft wide, and 7ft tall, with a floor in it it should be enough, headroom, at the front of the coachroof there wont be enough headroom, but berths and storage will most likely go there. With a completely flat bottom you lay the bottom panel down, stand the bulkheads up, and staple the rest of the panels down until they are dry. Then with the bulkheads down you put the deck on, the coachroof is all flat panels, and it has plenty of room inside and out. Personally I would put a steel center plate or a lifting bulb keel, with a steel plate I would add a skeg, so it still tracks strait with the board up, if you have a bulb keel it could lift and the draft still be under 2ft fully up. with a bulb keel it could be shorter, and with the weght centered down low, just as effective.

    Stubby
     

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  6. Kent Multer
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    Kent Multer Junior Member

    Interesting ... What's the length and displacement of this design? Also, who designed it? Has it ever been built?

    Thanks --
     
  7. stubby
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    stubby Junior Member

    length, 32ft, waterline length, about 30ft, displacment 2.487tons (can be adjusted with some changing of the shape). me and no.
     
  8. stubby
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    stubby Junior Member

    also I would put a yawl rig on it, as that allows SO many more sail combinations and it is proven to be easier to handle single handed.
     
  9. Kent Multer
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    Kent Multer Junior Member

    2.5 tons seems awfully light for a 32-footer with 7ft. of headroom; you might wanna check your math? Besides, measuring the draft with the board up is misleading, since it won't be sailed like that.

    The rig will be a cat-ketch or cat-schooner with 2 Chinese sails on free-standing masts. That's what I designed and built for my current boat (photo), and it works great. Self-tacking, and completely reefable from the cockpit. No winches, no stays/spreaders/chain plates.
     
  10. Kent Multer
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    Kent Multer Junior Member

    CORRECTION: I'll withdraw my comment about "misleading," since even leeboards need to be lowered when sailing. My main objections to a centerboard are the complexity of construction, difficulty of access for maintenance and repair, and obstruction of the interior.
     
  11. stubby
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    stubby Junior Member

    Yes I agree leeboards will be VERY easy to use, BUT, with a center case all you have to do is sandwich some 18mm bits of ply together, and as when you build a boat, you make it with floor boards, it will be just as easy/hard to maintain IMHO. If you go for a steel centerboard, it wont get damaged, and as soon as you hit anything it will swing back, so I think it would be perfect for your use.
     
  12. stubby
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    stubby Junior Member

    And with the draft I just took that strait of Delftship, I will do some reaserach on what the usual 32fter is and adjust it. I think a cat-ketch rig is perfect for your needs, and I wouldn't go for anything else.
     
  13. stubby
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    stubby Junior Member

    does 4.5tonnes sound better to you? considering it will probably be 9mm ply, it sounds ok
     
  14. Kent Multer
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    Kent Multer Junior Member

    Yes, 4.5 to 5 tons is more in line with my own preliminary numbers. Since you spelled it "tonnes," I should mention that I'm a Yankee, using Imperial measurements for everything. But I know what a mm is :^) .

    Isn't 9mm skin rather thin for a boat of this size? Sure it'll keep the water out, but I'd hate to bump into a dock-edge or hit a sunken log at any speed with 5 tons of momentum driving it.
     

  15. Kent Multer
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    Kent Multer Junior Member

    Hi folks --

    I figured that the Chinese sails will give the boat a distinctly Asian look, so I decided to try a "tunnel" roof like traditional junks. (see pic)

    But enough with the pretty pictures, I want to run some more numbers. How do I get Load Cases working in Delftship Free? Is this feature not included in the free version? Is there another piece of software I can use to check the stability of a design?

    Thanks --
     

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