How can this little single chine plywood row/sail skiff be improved?

Discussion in 'Boat Design' started by BayBoater, May 31, 2018.

  1. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    I will be happy to help you, if you need anything about naval architecture, for this project or for future projects.
    I downloaded FreeShip (and DELFTship), I worked a little, very little, with it and it seems to give totally correct results. With all due respect, find out if you are doing everything right.
     
  2. BayBoater
    Joined: May 2016
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    BayBoater Junior Member

    I'm totally not sure that I'm doing everything right with Freeship; it comes with a pdf help file but there isn't much info in there about creating parts that aren't integral with the hull.

    For forming the people I just extruded a surface from the edge of the hull, shaped it, and then deleted the connection. I have absolutely no idea if it is the only (or best) way of creating people. I still haven't tried to create a sail, but maybe it could be done the same way.

    If I create a sail I imagine I could find out with the program how much the weight of the sail and spars would destabilize the boat, but I'm not sure there would be a way to estimate the heeling forces created by the wind (as to not overpower the righting forces of the boat combined with the sailor hiked out on the rail. I created a mast once by adding a cylinder but found tapering it a bit difficult because it was raked. Maybe taper first, rake afterwards by rotating?

    I've uploaded the people here as a part, can you pick up the file from the forum? I just added them to another hull, and as soon as I moved them so that the bottoms of the feet go went below the waterline (but totally inside the boat) the curve of cross sectional areas got distorted.
     

    Attached Files:

  3. TANSL
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    TANSL Senior Member

    I'm sorry but I can not open the "2people.part" file. My version of FreeShip does not support ".part" files.
    I think that to calculate hydrostatic, you should forget about the two people. Nor should you need to model the mast or the sails to perform those calculations. .
    The calculations of heeling due to wind and heeling by passengers to a band are somewhat more complicated than FreeShip can handle. But, as I said, I do not know the possibilities offered by FreeShip to the designer.
     
  4. RumnCoke
    Joined: Aug 2013
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    RumnCoke Junior Member

    I don't know. Considering the amount of weight you may carry and the size of the boat there is not that much you have to work with. Under sail, a longer water line is always a positive. Your boat opens up from the bow very quickly at the sheer line, but down below at the waterline has a more narrow profile. You might try to open up from station 7 and onward to at the waterline and below to achieve a fuller bow section. Instead of having such a faired curve from bow to keel line, bring the bow down straight vertical and reduce the rocker in this frontal area. It doesn't have to be radical, just open it up to a similar line like you have at the deck line. Longer waterline more speed. You can do all of those alterations easily from Freeship and then test to see the results. Food for thought. For ease of building, straight lines at the transom seems very practical.
     
  5. RumnCoke
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    RumnCoke Junior Member

    While your calculations may be accurate for two people in the boat now, you should consider the weight of sails mast and any rigging. Its not light and it would be some place way forward in the bow. Don't know if you intend to sail with two people.
    Tender 23 | Boat Design Net https://www.boatdesign.net/gallery/tender-23.23251/ This is the type of fore section and bow style I was referring to. It would not take a lot of work to redo a few sections forward see the results.
    Notice the very vertical lines down from the shear line and the very vertical bow. A lot more floatation there.
     
  6. BayBoater
    Joined: May 2016
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    BayBoater Junior Member

    Several folks suggested making the sides of the transom straight instead of curved, and I did that; it will most certainly be easier to build that way.

    I envision mostly one person rowing, sometimes one rowing with passenger, but only one sailing. I expect the sailing gear to weigh less than a person. This past weekend I cut a 10' (3m) mast blank out and it is pretty heavy, but not yet rounded.

    I'm definitely more drawn to the look of the chine becoming softer and disappearing into the flare near the bow more like this Pete Culler boat (Plans at Mystic Seaport) than the plumb-stemmed dinghy in the link. Culler Vee bottom yawlboat lines Mystic.jpg

    I was just hoping to make mine a bit faster under sail than the Pete Culler boat, which is bigger (12'6" (3.8m) length, 5' (1.5m) beam), much heavier because it is traditionally built, and purely a displacement hull as far as I can tell.

    If I make the chine wider in the front half of the boat, with the knuckle harder and further into into the bow, it would be a sharper bend for the plywood. Last weekend I made a cardboard model trying exactly that, but didn't like the look of it. One might have to cut the bottom and sides apart almost completely, which is what I was trying to avoid. There is another similar design out there, Martha's Tender, that is built on chine stringers. Tenders - Prams - Martha's Tender https://www.woodenboatstore.com/product/plan_Marthas_Tender/tenders_-_prams . The chine knuckle of Martha's Tender carries right into the bow and the bottom and side panels are completely separate.
     
  7. RumnCoke
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    RumnCoke Junior Member

    Thanks for your reply. Yes, I can see your actual construction problem with the bend and chine. Your preferences, your boat and your sweat. :D. Hope to see the finished product. Good Luck.
     
  8. David J Ritchie
    Joined: Jan 2018
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    Location: Victoria BC Canada

    David J Ritchie Junior Member

    Nice mock up and plans BayBoater good work

    I can't tell with the mockup but in your side profile drawing i think your mid ship makes a dip down too low too soon. I would carry more of that generous bow hight back closer to the stern even by a foot or so. That should get you closer to the wave handling capability your design deserves.
     
  9. BayBoater
    Joined: May 2016
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    BayBoater Junior Member

    I agree with your analyis. I just tried that, but unfortunately this makes the side panels slightly wider, and the boat no longer fits on two plywood sheets. There really isn't any wiggle room change much.

    This little thing is intended to be economical and quick to build. I think I will just build it with minor modifications and if I find out by using it that the shape is really promising but just not quite there yet, I'll revisit the design.
     

  10. David J Ritchie
    Joined: Jan 2018
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    Location: Victoria BC Canada

    David J Ritchie Junior Member

    makes sense good luck and have fun building
     
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