scaling a design by 10%

Discussion in 'Boat Design' started by TimothyM, Aug 23, 2010.

  1. TimothyM
    Joined: Jul 2010
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    Location: Maine

    TimothyM Junior Member

    Any thoughts on scaling this Atkin design 10%? I really like the boat, but I'd like it better around 18ft. If I scale down everything by 10% would it work out?

    James Samuel is 20 feet 1 inch overall by 19 feet on her waterline by 7 feet 2 inches beam and 7 inches draft with the centerboard housed. The freeboard is 2 feet 7 inches at the bow and 2 feet at the stern. It is obvious that she is truly a big skiff, a load-carrier of considerable ability and an all-around practical boat.
     

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  2. gonzo
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    gonzo Senior Member

    You should scale down the sail area by about 20%.
     
  3. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    Tim,

    Why do you feel the need to drop off two feet, is it because of garasge space? If not , build it to size, it will be nicer if left alone unless you HAVE to make it fit somewhere. Bigger boats are nicer generally.
     
  4. TimothyM
    Joined: Jul 2010
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    TimothyM Junior Member

    my shop space and I have a trailer for another boat that will work better with 18ft.
     
  5. NoEyeDeer
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    NoEyeDeer Senior Member

    For a chunky beast like that it'll work. The resulting 6"6" beam will be adequate for an 18 footer.The result will be slightly overcanvassed if you scale the rig by the same proportions but you can always reef it.
     
  6. philSweet
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    philSweet Senior Member

    If you plan to build her out of the same planking material specified and you like the load carrying capacity, consider scaling her by 5% and lopping a foot off the back. You should check the bending radius of the planking. I'd allow for 100% of that centerboard though. crew weight provides most of the righting moment and that will change less than the scaling factor, so you can retain all of the mast height if you provide adequate board area. If you drop a size in the planking, it is worth the effort to try to match the bendyness of the new planking to the new radius. I'm assuming you can choose between okoume, meranti, and fir marine ply in any given size. I'm also assuming that no internal ballast is specified and the CB is wood. Again, if capacity is important, you might not want to reduce the freeboard at all (but she appears to have plenty, so you could if you wanted to).
     
  7. NoEyeDeer
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    NoEyeDeer Senior Member

    Actually if you want a big and capable traditional American working skiff then the one on page 319 of Chapelle's American Small Sailing Craft is a much better boat IMO. It would sail rings around the Atkins boat.
     
  8. TimothyM
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    TimothyM Junior Member

    I have no eye deer what that boat is like. Can you tell me more about the design? maybe a name, so I can find a picture online?
     
  9. NoEyeDeer
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    NoEyeDeer Senior Member

    Unfortunately the only name given in the book is Chesapeake bay skiff, which is a name that would cover a lot of different boats. The Smithsonian would have the plans for it and my guess is that they would be in the "Ship Plans List/Maritime Collection". http://americanhistory.si.edu/csr/shipplan.htm

    If you feel like spending $20 you'll get more study plans than you know what to do with. :D I've done a bit of Googling and can't find the exact boat online, but details from the book are:

    Chesapeake Bay Skiff

    LOA: 20' 3"
    Beam: 6' 7"

    Built at Bishop's Head in 1911 by William Reeves.

    The caption says: Fig. 114. Tonging skiff of a size and type once popular on the Eastern Shore of Maryland.
     
  10. TimothyM
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    TimothyM Junior Member

    Is it a Cat rig? I would have to scale this down also. I really want to keep the length to around 18ft
     

  11. NoEyeDeer
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    NoEyeDeer Senior Member

    Yes it's a cat rig. Most of the smaller skiffs were.
     
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