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Thread: My ideal boat - trying to design my own hull.

  1. #1
    Join Date
    Apr 2012
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    Default My ideal boat - trying to design my own hull.

    After may last built I feel like I have to try to draw my own boat.
    Mind you I am just tossing around ideas and have no clue about what works and what not so I am just gonna post, draw, ask questions, draw, post,...that should be enough to entertain me through winter and maybe I get to sail something when it gets warm again.

    What?
    • LOA 330cm-360cm (11'-12')
    • beam 110cm-120cm
    • nesting in 4 parts.
    • very easy to build
    • no glass, just some epoxy.

  2. #2
    Join Date
    Oct 2008
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    Walney, near Cumbria UK
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    Default Re: My ideal boat - trying to design my own hull.

    Average proportions call for more beam, 1.4 at 3.3m to 1.5 at 3.6m according to Ian Nicholson.
    It really is quite difficult to build an ugly wooden boat.

    The power of the web: Anyone can post anything on the web
    The weakness of the web: Anyone can post anything on the web.

  3. #3
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    Apr 2012
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    Default Re: My ideal boat - trying to design my own hull.

    My last boat was a copy of the PT-11 dinghy split in 4 parts and it just fits my trunk.
    Nice boat but I need to change some things about the hull shape.
    It is a little too wide.
    7 panels are too much.

    There are 2, possibly 3 designs I like for some aspects.
    Mayfly 12
    I guess I don't need that much freeboard and I do want less rocker. A little narrow aft. The sides are not at an constant angle to the floor board like in the Mayfly 14.
    Summer Breeze
    A little too wide, twisted side panels.

    I would like to take the bottom shape of the PT-11, just the 3 lowest panels and make it one flat bottom. Maybe add a V shape forward of the dagger board. Or just flat stern to bow?
    The daggerboard slot should move to one side so that the bow quarter can nest into the piece with the daggerboard. Any concerns about offset daggerboards?
    Then just two boards up at a an constant angle, meeting at the bow...I will cut a round stem there, rather wide at the top, almost vertical in the profile.
    The gunnels will be plywood, maybe cnc cut, not one length but to fit each separate part. For that to work nicely they have to be perpendicular to my side panels. I just tried to draw that...I just need to cut my hull with a flat plane 90 to my sides....works well and yields a nice sheer line if the panel has an angle of 100-115 from the bottom.

    What will a wide bottom aft do to my boat? Is there a rule of thumb for volume distribution? I've sailed some different dinghies and I have a feeling that you can balance any rather small boat very well with your body weight. I don't want a sailing canoe, needs to look like a real boat with a wider stern.

    Here's some comparison between the PT-11 and a slightly altered Mayfly12.

    Test001.jpgTest002.jpgTest003.jpg

  4. #4
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    Default Re: My ideal boat - trying to design my own hull.

    The beam just can't be wider than 120cm.
    Bolgers Teal is also another example of what I have in mind. There are even Teals with offset daggerboards, don't know the original plans (http://workingsail.com/boats/teal/index.html maybe Bolger specified a leeboard?).
    https://www.google.at/search?q=bolge...6Mcl4craXGYbM:
    Last edited by heavyweather; 09-30-2017 at 07:00 PM.

  5. #5
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    Default Re: My ideal boat - trying to design my own hull.

    Test004.jpgTest005.jpgTest006.jpg

    Some crude drawings of the different hull forms I am looking at.
    Flat bottom, V-bottom and flat-to-V.
    The left hull in the first picture is the PT-11 I use for reference for the size of the bottom.

    Any advice on volume distribution, rocker and hullform? My hulls do have a little more volume forward than the PT-11 but a much wider stern than either the Mayfly12, SummerBreeze and obviously the Teal.

  6. #6

    Default Re: My ideal boat - trying to design my own hull.

    If it will be plywood, consider including fiberglass. 20-some years ago I omitted the glass from my cuddy cabin - went with poxy and paint. The plywood split and checked. I just cut the cuddy cabin off the other day - the cuddy is in the dump.



  7. #7
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    Default Re: My ideal boat - trying to design my own hull.

    My last hull is completely glassed.
    My boats are only in the water for hours. I just want to try paint only once. It may only last some years but it is totally experimental anyways.
    20years doesn't sound bad at all. The total cost of my hull will be under 100€ without glass and should go together in hours.

    Can you explain the word "checked" to me? It swelled on the surface and the paint came off?


    Another design idea. I want to try a collapsible centerboard case/daggerboard case so that it still can go in the middle.

  8. #8
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    Default Re: My ideal boat - trying to design my own hull.

    I've read about Herreshoff designs that got more volume distributed forward that the bow comes up better in a turn. That design should go better windward. I might go with a smaller bottom aft.

  9. #9

    Default Re: My ideal boat - trying to design my own hull.

    I use the term "check" to describe wood splinters peeling up from the surface. In plywood they range in size from micro-splinters up to large toothpicks. In solid wood they can be the size of a finger.

  10. #10
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    May 2015
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    Default Re: My ideal boat - trying to design my own hull.

    What will be the intended use and expectations from this hull in terms of speed, load carrying ability, stability? Will it be sailed, rowed, take an outboard or all three?
    Different answers might yield very different hull shapes, especially in the length and beam limits you have specified.

    The 10ft Duo by Richard Woods is another possible shape, a flat bottom that blends into a a shallow V aft.

    The ideal volume distribution depends on the speed regime that the hull will be optimised for. Hulls with fine ends generally excell at displacement speeds and if designed with low wetted area will require very little drive to move right along. Try and calculate the prismatic coefficient for the PT11 as well as its wetted area and use those values as a start if you want comparable performance.

  11. #11
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    Default Re: My ideal boat - trying to design my own hull.

    A hull that is as much fun as possible to sail. Planing if that is possible or should I just go for good displacement speed? The Duo is very nice but could be a little wider and longer.
    Priority is still very easy to built...3, max 4 panels. Not too small or too low, don't need water in the boat nor do I want a sailboard or sit on the sides.

    Test007.jpg

    I am sailing on Alte Donau in Vienna. Sheltered, not much wind most of the time, shore is never more than 50m away.
    No motors allowed, no rowing. Might do a section for the Mirage drive some day.
    Last edited by heavyweather; 10-09-2017 at 08:54 AM.

  12. #12
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    Apr 2010
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    South Australia and Tasmania
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    Default Re: My ideal boat - trying to design my own hull.

    4 part nesting with a collapsible centreboard and you want to build it in hours, all for under 100 euros? Good luck with that.

  13. #13
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    Default Re: My ideal boat - trying to design my own hull.

    Thank you PhilY.

  14. #14
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    May 2010
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    Chicago
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    Default Re: My ideal boat - trying to design my own hull.

    my 2 cents: I am building to a set of lines from Chapelle / Smithsonian so the shape is determined, but there were no construction plans for the "Western Lakes Mackinaw." I have spent a HUGE amount of time wading through conflicting scantling advice and alternate configuration possibilities on how to build this thing. Be warned.

    Ken

  15. #15
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    St. Simon\'s Island, GA, USA
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    Default Re: My ideal boat - trying to design my own hull.

    Don't do it. After you have designed your own boat, and built it, about five times, you may, just may, design and build a half decent boat. Life is too short, and there a lot of good designs to suit every purse and taste.

    This even applies to flat bottom skiffs. A good one is a joy and delight, but they are rare. Most are dogs, probably built by home designers.

  16. #16
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    Default Re: My ideal boat - trying to design my own hull.

    It makes me a bit uncomfortable that you are calling your boat a "copy" of the PT 11. It's not a copy. I think I know how you developed the panel profiles, but neither the hull shape nor anything else about the boat is a PT 11. I think that what you are doing is interesting and I have enjoyed following the development of your boat, but I hope that you will call your boat your own design.

  17. #17

    Default Re: My ideal boat - trying to design my own hull.

    Quote Originally Posted by ahp View Post
    Don't do it... Life is too short
    I lived the first 50 years of my life under the impression that life is too short - runnin around all crazy in the rat race tryin to fit 100 years of living into 50 years. Then I retired.

    The epiphany came when I decompressed, had a ton of time, and realized, holy crap, life is long.

    Perhaps the most rewarding time of my life was the 20 or so months that I spent designing and building my boat. Especially when I delayed the completion a year, just to relax and enjoy the build.

    One day my neighbor teased me by asking, "Are you ever gonna finish that boat?" My answer - "When I finish, then what will I do?" So, what the hell is wrong with rebuilding it five times?

    Enjoy the design/build, and the rebuild, and the rebuild, and the rebuild, and the rebuild, and the rebuild.

    BTW my design/build turned out OK.


  18. #18
    Join Date
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    Default Re: My ideal boat - trying to design my own hull.

    Quote Originally Posted by heavyweather View Post
    A hull that is as much fun as possible to sail. Planing if that is possible or should I just go for good displacement speed? The Duo is very nice but could be a little wider and longer.
    Priority is still very easy to built...3, max 4 panels. Not too small or too low, don't need water in the boat nor do I want a sailboard or sit on the sides.

    Test007.jpg

    I am sailing on Alte Donau in Vienna. Sheltered, not much wind most of the time, shore is never more than 50m away.
    No motors allowed, no rowing. Might do a section for the Mirage drive some day.
    In a light wind location like that planing will be rare in a boat you don't want to sit out on. It will be even rarer with the extreme aft rocker in some of your designs.

    Herreshoff did some nice dinghies but that was almost 100 years ago, at a time when technology meant that performance dinghies required a very different shape to modern ones. Nor did Herreshoff design boats for very constricted waterways as far as I am aware. A Jack Holt design is probably a much more useful inspiration since his boats work very well in such environments and were designed with the benefit of decades more experience in dinghy designs.

  19. #19
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    Apr 2012
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    440

    Default Re: My ideal boat - trying to design my own hull.

    Russell,
    I can call the boat anything you like.
    Then it's my design based on anything I could find on your design.
    First I took all photos and the one drawing I found. I processed the photos with photometric software to get some measurements (angles and relations), then I used the EXIF data (for focal length and distortion correction) to compare the resulting CAD drawing to the original photo in original perspective.
    Then I found a cad drawing (small PNG file If I remember) of the hull panels on your websites. I then compared my unrolled hull to what I suppose is the original cutting data?
    I figured calling it my design would be rather respect less but if you like I won't mention the PT-11 anymore in regards to my resulting hull. I can also mail you my cad drawings if you are interested, would be interesting for me too to see how near I came with my process.



    Thank you Poxy,

    I do get much more time building boats (or anything like RC planes) than actually using them anyways so the most Joy is in the building and tinkering anyways.
    Very nice boat you got there, I hope you enjoy using it as much as building. Are you building something right now?
    (I was nicknamed Poxy in University bc I was always doing Epoxy stuff...)

    Chris,
    I guess I will just go with a non planning hull then.
    What's the use of much aft rocker like in the Mayfly 12?
    Can only guess that it reduces lateral resistance aft and easier turning when not heeled?
    It probably doesn't matter much for my "sailing" anyways...I just like to give some thought to things and have fun doing so.


    ahp,
    Any suggestions for a suitable hull? I already listed anything I consider inspiration but nothing suits my needs enough/in all points.

  20. #20

    Default Re: My ideal boat - trying to design my own hull.

    Quote Originally Posted by heavyweather View Post
    Are you building something right now?
    I am always building something. Depending on how you define "rebuilding", I am rebuilding, for the fourth time, a boat I built 25 years ago.

    The first version I built was a hull designed by a reputable marine architect with my wheelhouse design.





    Turns out I made her too bow heavy. I used her for a few seasons then family came along and the babies needed shelter so I moved the center-of-gravity back and converted her to a cuddy cabin.






    After a few seasons, I got tired of getting hit in the face with spray when quartering into a head sea (on my usual route) so I added a windshield.







    Now the kids are gone and I am tired of surfing a flat-bottom boat in following seas and tight-roping around that cuddy so I am converting her to a semi-vee with a pilothouse console.






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