Help designing a knockabout 3.4m cat dinghy with FREESHIP

Discussion in 'Boat Design' started by catdinghy, Sep 11, 2013.

  1. catdinghy
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    catdinghy Junior Member

    Thanks

    I'll give that a miss on a one off ;)

    Why? Stiffen the panel, buoyancy or both?
    Remember any excess weight is bad in my opinion anyways
    .
    Doesnt add strength though does it? So surely a 2 to 300gsm DB would be better?
    Thanks, a bit of extra structure internally compared to what I wanted, but I think I am starting to lean towards a v nosed flattie.
    I was always impressed at what my 8x4 flattie did before, so a 4ft longer, 1 ft wider Vnosed version should be better again
     
  2. philSweet
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    philSweet Senior Member

    pictures of the little one are here- http://www.boatdesign.net/forums/boat-design/teotwawki-boat-42752-2.html post #28

    edit To answer next bunch of questions, yes to stiffen, keep feet and gear dry, and provide a sump. Also, it is just as likely to get holed through from the inside as the outside on a little dink. So no worries if you need to haul a big ugly chunk of something. One unexpected benefit of the cat dink design is the ability to have a clean side and a dirty side. You can carry a dead genset in and still bring the laundry back.

    The Dynel is good nonskid, but doesn't clean real easy, if that's an issue with this dink.
     
  3. catdinghy
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    catdinghy Junior Member

    Option 2
    A v nosed flattie
    At the end of the day an easier build and it should be able to carry more load and should be as stable as the cat dinghy I would think.
     

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  4. Mr Efficiency
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    Mr Efficiency Senior Member

    I'd put about about 5 degrees of vee in at the transom, rather than dead flat, that looks pretty good imo, will be stable and good for a short excursion or two. And as you say, an easier build.
     
  5. catdinghy
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    catdinghy Junior Member

    Reason?
    There is a smidgen of v in the bum, more poor drawing than intentional
     
  6. dskira

    dskira Previous Member

    [​IMG]

    Must be a very noisy hull and with some stabilty probleme if you lean over.
    I will see this configuration for a larger boat.
    A prototype will be nice, and hope it will prove me wrong.
    Nice rendering
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    You want it to bank a little in turns, and not have the tail skate around and dig the chines in, will help it track better on plane. Don't forget to rake your transom about 13 degrees at least.
     
  8. lewisboats
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    lewisboats Obsessed Member

    This is something I played with a couple of years ago... food for thought.
     

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  9. lewisboats
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    lewisboats Obsessed Member

    Outboards are set up to be optimal with 13-15 degrees of rake. Not enough rake and you can't tuck the motor in properly... which leaves the prop pointed at an angle towards the surface, driving the back end of the boat down.
     
  10. catdinghy
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    catdinghy Junior Member

    Well, I suppose that the next question, how do you set 15 degrees for the transom rake?
     
  11. lewisboats
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    lewisboats Obsessed Member

    1:1=45 deg, 1:2=22.5 deg, 1:3=15 deg so in this case for every inch off of vertical you measure up three inches. A 15" transom will be off vertical 5"
     
  12. catdinghy
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    catdinghy Junior Member

    Thanks, still couldnt get my head around it as, and obviously I am dong this wrong, this transom is 700mm high so 27.5 inches high.
    If a 15 inch transom is 5 inches off vertical then a 25 inch transom is 8.3 off vertical?
    So 210mm in from vertical? Is that right?
     
  13. catdinghy
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    catdinghy Junior Member

    And whats going on here?

    What is this mystery "side part 1 (port)"
    It doesnt show in the line drawings, just the plates.
     

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  14. lewisboats
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    lewisboats Obsessed Member

    Yes... so your 27.5 transom is off 233 mm. However... you won't find a motor with a leg that will fit just that so you will have to provide a transom cut out to fit the motor. The closest is 25 inch but those are harder to find and more expensive. I would go with a 20 inch and a splash well behind it.
     

  15. lewisboats
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    lewisboats Obsessed Member

    Turn on interior edges and then go into layers and uncheck the bottom and the transom. After that go back and highlight the meshes until you find the part that fits. I think you have too sharp an area or one that it can't translate into a whole panel. The same thing with your transom... it should be one piece. You have one or more points out of alignment which makes it a 3d surface so it breaks it up into two pieces. Attach your file and I'll take a peek at it and see if I can find the discrepancy.
     
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