Question about curvature of hull

Discussion in 'Boatbuilding' started by declan, Feb 2, 2013.

  1. declan
    Joined: Jun 2010
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    declan Junior Member

    Hi everyone!

    I'm still building the DuckSkiff. I've cut out all the pieces and joined the panels together using fiberglass butt joints, a la this guide.

    This might be a little tricky for me to explain because I don't know the terminology well, but the hull is composed of two identical sides, like one is a mirror image of the other across the keel. So it looks like this:

    [​IMG]

    Which is what I cut out. Then, the guide has all these pictures of completed boats at the back. So I was looking at them and saw these pictures:

    [​IMG]

    Which, I realized, you can't possibly make with the pieces the guide told me to cut out. With mine, you can have a V shape to the hull, but no curvature front front to back, or you can have that front to back curvature, but a flat bottom. To have both of those, like the boat in those pictures has, you would need to taper the front of the two hull panels, something like this I think (please excuse the crappy shop job):

    [​IMG]

    I googled for some pictures of the Duck Skiff and found this, and was immediately horrified because...well, I'm not a huge fan of how that boat looks, to put it nicely (Captain Jay Kavanaugh, if you're reading this, I'm real sorry). It looks really boxy to me, not like the nice pictures of (the totally different) boat above.

    So, apparently the plans call for the latter of the two options you can have with the hull panels they've directed me to make:

    [​IMG]

    This is definitely nicer looking to me than the one from that forum, but it'd be even better to have it like the boat in the first picture, V shape and front to back curvature.

    So my question is, how hard is it to make that tapering at the front effectively? I know I could eyeball a shape and do it, but that also has the potential to come out horrifically. Should I even bother?

    (also, I know that the plans are entirely volunteered and just something someone did to be nice, but putting pictures of different boats in there is pretty confusing...)
     
  2. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Hmmmmm, There are all sorts of "duck skiffs" listed on google. I cannot determine which of them that you are wrestling with. Let me try to determine what this one is all about. I get that your instructions will not make the boat shown in the incredibly messy workspace picture, the one with all the tie wraps showing. The other pictures of the inverted boat on a building jig looks more like it. Your bottom parts will make that boat. The bottom will not curve upward near the front when viewed from the side.

    You have to decide whether your boat must look the way you want it to look or whether your boat is to be best suited for the application and the set of plans that you have. You may not be able to have it both ways. Dont sweat the longitudinal curvature, If the bow section is kept in the water, the boat will be quieter when at rest. The designer may very well have taken noise into consideration. Here I presume that the boat is for duck hunting.

    One of your drawings shows a boat that, viewed from the side, has the bottom curved upward at both ends. That curve is called rocker. Such a boat is going to be a displacement type and it is going to be efficient at slow speeds only. So if you are planning to go fast, upward curve at the back end of the bottom is a definite no-no. If I am interpreting your remarks correctly, it seems that you want rocker in both ends of the boat. OK so you are going to have a boat that is slow but will row or pole fairly well. You could use a very small outboard or a really small Go Devil or Mud Buddy. Just don't expect more than 5 or 6 miles per hour from such a design..

    Now if you plan to use a larger motor, wish to go faster, and are not primarily interested in rowing, then the bottom needs to be staight ,no rocker. The vee sections are not necessary and a perfectly flat bottom will do alright. The flat bottom will be noisier and it will slam harder and louder at speed. The little bit of vee in the inverted boat picture will help a little but not much. In that picture the bottom appers to transition to a flat or near flat area. That is fine and it will plane with a smaller motor than it would if it had a lot of vee at the transom.

    Post more information about the size of the boat, the intended specific use, and the power that you will use. Then we might be able to be more helpful.
     
  3. alan white
    Joined: Mar 2007
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    Location: maine

    alan white Senior Member

    Flat iron skiffs are pretty efficient at low speeds. The vee section bow you have supplied to you would be better suited to a boat that moves through chop at speed. Why those pictures are different is probably due to the fact that their reason for being there is to assist in panel construction. Otherwise I imagine the stitch method wouldn't be shown, but instead a photo of the finished boat.
    The vee bottom boat probably has no rocker aft and a wider stern. In other words, a planing hull that might be a bit balky to row or motor electrically or with a small (5 hp) motor.
     
  4. kvsgkvng
    Joined: Jan 2012
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    kvsgkvng Senior Member

    I think if you plan using this boat on a flat water, it doesn't matter no matter if there is rocker or not. But if you plan using this boat in bays, then you will see big difference in flat hull pounding even in slight chop. V- section helps to bring bow in the water gradually while building buoyancy with more gentle motions. Flat bottom would slap mercilessly with noise and splashes...

    If you need to unfold panels -- please post the model file and I can do it for you, both in Delftship printout output and DXF-file export.
     
  5. rick gray
    Joined: Dec 2012
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    Location: port coquitlam B.C.

    rick gray Junior Member

    wire framing? i have seen it done for aluminium small boats to 22 ft' the builder used thin metal lond rods to simulate the desired deck shape/shear,the centerline keel and stem, the chine,and conical style (straight frame lines . to create the wire frame model, then changed as desired from looks of hull. he wraped cardboard on mockup to get faired shapes, then added framing flatbar etc ,keel ,stringers and breasthooks .alumininium plate was cut and formed to fit. of course the wire frame was removed first. it would work with wood battens to make a frame work to wrap cardboard on. gets good hull shapes.
     
  6. declan
    Joined: Jun 2010
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    Location: USA

    declan Junior Member

    Hi, thank you for the response! The one I'm doing is from here, though the PDF of the plans no longer seems to exist there: http://www.duckworksbbs.com/plans/lewis/duckskiff/index.htm

    I mainly want this boat just to row around smallish bodies of water. Maybe someday I'll get one of those tiny motors, but that's a secondary consideration. So I'm definitely okay with a boat only designed for slow movement. So, the plans I showed here show a bottom that has a rocker, but no V, correct? If so, it still seems like it'll look different from the upside-down boat on that forum, because that one doesn't even seem to have a rocker.
     

  7. lewisboats
    Joined: Oct 2002
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    Location: Iowa

    lewisboats Obsessed Member

    That is MY design. The pictures are there strictly to illustrate the method of Stitch and Glue and do not depict the construction of a DuckSkiff, as stated in the PDF. Perhaps you missed this...
    The hull shown is for a boat called the Fisher10 and were the only pictures that I had that depicted the stitch and glue method that were my photos... at the time. I wished to illustrate how a hull can be stitched together using simple wire ties. I don't know where you got the instructions for the DuckSkiff but the PDF that I made clearly shows the hull form that the boat should be. If you got them other than Duckworks please let me know as they are the ONLY place that you should have gotten them from. If you got them more than 6 or so months ago, I apologize for the confusion but there is now a picture of a completed hull (below) on the page. The PDF plans are still available from the link YOU supplied. The plans show a boat that has either rocker for a displacement hull or no rocker in a planing hull... the offsets are given for both. Make sure you get the corrected table of offsets in the .txt file that is on the plans page. There was an error in the original that has been corrected.

    The quotes above are taken directly from the posted PDF in the link you supplied...today.

    Here is the photo referenced above:
    This is of a hull with rocker for rowing or a trolling motor as shown (mounted fore or aft).
    [​IMG]




    and some others of the same boat:

    [​IMG]

    [​IMG]

    [​IMG]

    a high quality build of the boat as designed.

    Here is a picture of Fisher10 at it's launch... a very different boat.

    [​IMG]

    capable of 25 mph with a 9.9 hp motor full bull.
     
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