Help with a simple skiff design

Discussion in 'Boat Design' started by IronClad, Aug 4, 2016.

  1. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    As far as I understand IronClad understood that there can be no twist in the bottom which is absolutely not correct.

    The pretty extreme concave shape in the Flint image I posted is not tortured by the way. It is twisted but it does not have compound curvature, you can place a ruler flat even on the concave sections you just need to place it diagonally.
     
  2. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Ok, let's be happy each with their idea. End of this story, as far as I'm concerned.
     
  3. PAR
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    PAR Yacht Designer/Builder

    There's no "ideas" here, just developed shapes.
     
  4. rnlock
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    rnlock Junior Member

    Maybe it wasn't a problem, but I apologize that I didn't indicate I switched to addressing the OP at the start of the third paragraph of my previous post.
    I'm not quite sure which boat I mentioned you thought was a displacement boat, though I'll admit the TIMS is one! With the power available at the messabout, even a partial section didn't exceed maybe 3 knots, and the whole thing was probably even slower. But the scantlings wouldn't have been the weak point. Rather, it was the attachment between sections. The TIMS was never anything more than a stunt, but it was fun.

    The other boats I mentioned, including the Folding Schooner, all plane. Or, at least, I'd be extremely surprised if it didn't!

    I've been on a Sneakeasy that was planing very nicely, if not terribly fast on a 10 hp four stroke. Bolger, who designed it, estimated it will do about 25mph with the recommended 25hp motor. The bottom is 1/2 inch thick. Obviously it's not meant for punching into big waves!
    http://www.boats.backwater.org/Sneakeasy/

    While Bolger doesn't mention that the Folding Schooner planes, her little sister, the Light Schooner (aka Scooner), which appears from the plans to use about as much plywood (it's built more heavily), and which has a similar rig, has been clocked at 16 knots! http://www.ace.net.au/schooner/tipsndx.htm#start I wouldn't want to punch the Folding Schooner into big waves either, but it was designed for a schooner race which, for Bolger, was local. (i.e. in the ocean)

    I mentioned that the the two skiffs have very heavy bottoms. On the Clam Skiff, it's 2 1/2" thick where the wide shoe is, and 1 inch elsewhere. THey're meant to bounce off rocks. The Diablo, another planing Bolger design about the same size, uses only 1/2 inch on the bottom and 1/4 inch on the bilge panels.


    Unless he uses enough framing to prevent it. At a younger age, I drove an 18 foot aluminum runabout, a fairly heavy boat, into a good sized chop. The slamming was impressive. But the OP intends this boat for "rivers and protected inshore flats".
    [/QUOTE]
     
  5. PAR
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    PAR Yacht Designer/Builder

    A sailboat on plane doesn't experience the slamming loads a powerboat does, which was my point. Scantlings for a powerboat that's capable of exceeding 25 knots, rise substantially over a displacement version of similar configuration. You really can't compare scantlings between designs like that effectively, unless the design approuch is similar. For example the Bolger Clam Skiff is much like many clam skiffs (including mine), but also employs a fat cutwater, which he was fond of and of dubious value. The Diablo is a wholly different approuch and frankly there's no real comparison to the clam skiff, though does have a fair bit in common with his small schooners.
     
  6. rnlock
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    rnlock Junior Member

    Actually, the OP wrote 25mph. 25 knots is almost 29 mph and about 32 percent more kinetic energy to deal with.

    I wasn't really suggesting that anyone would go 25mph in a Folding Schooner. I was just getting a bit carried away. Bolger wrote that it sailed at least as well with a 1/2" thick bottom, so maybe... BTW, the original design has extra lumber on the bottom. Looks like the widest space between that support is only a foot. I think if I was going 25 mph in a Folding Schooner, I'd start worrying about the aerodynamics! It's very light.
     
  7. IronClad
    Joined: Aug 2016
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    IronClad Junior Member

    Thanks everyone for the replys! You have all given me some points to think about. I think I'm going to follow the general advice I seem to be getting and scale the craft down slightly and lower my speed 'requirements' to be more in line with 4-6 hp.

    Thinking something like 3.5' max bottom with ~4.25' max beam, but still 15'or 16' feet long, and looking for 10-15 MPH max speed. I'd want this to be 'car top-able.' Earlier it was mentioned about initial stability, but I'm coming from a 17'x36" canoe with a trolling motor, so provided I'm more stable than that (I stand up and cast in it on calm water)... I'm also planning to simplify the design a little.

    I did a lot of digging on like designs and sat down with a lot of study plans and specs over the last few days... Bateau's Flats Stalker 18 is I think what I was originally going for without knowing it, but my criteria is more in line with their Indian River 15. That said, I don't want to buy and use their design... but if this goes well I'm going to build an FS18 next.


    I'll post some re-design pics when I have them ready.
     
  8. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    You mentioned a 17' foot canoe... lol... My favorite boat is/was my plastic canoe 18'x3 with a 5 hp outboard.. it is fast... and i have crossed several very large bodies of waters with it... and many have said prayers on it...

    If you are thinking about a car portable boat , take a look at these http://www.christinedemerchant.com/boat-styles-take-apart.html
     
  9. IronClad
    Joined: Aug 2016
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    IronClad Junior Member

    Switched CAD programs, made some changes, played around with it to get a good idea of what it would look like... It's great being able to change any dimension of the hull and have it change everything right with it!

    Basic specs on the redesign:

    Max bottom width: 44"
    Max Beam: 52"
    Length 16'
    **Estimated weight ~108 lbs as drawn.
    Flat bottom.

    Also, if it looks like it "should" be a single long board, it is. Bottom may be made from 3/8" ply instead of 1/4. Either way I plan to fiberglass it top and bottom.
     

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  10. IronClad
    Joined: Aug 2016
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    IronClad Junior Member

    I've taken my old Grumman canoe into places it was never meant to be and caught a lot of fish with it. It goes around 4 MPH with the 30 lb motor.
     

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