New but wanting to learn, advice on methods needed

Discussion in 'Boat Design' started by SNEAKINDEACON, May 29, 2014.

  1. SNEAKINDEACON
    Joined: May 2014
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    Location: Tampa, FL

    SNEAKINDEACON New Member

    I wanted to make a tunnel hull skiff about 22'...this would be my first personal build, i've helped my father years ago with 3 different tremblay mullet fishing boats but thats really the extent of it.

    I want to do a couple of things..self bailing hull being first and foremost, I know the ride of my design in choppy water will be a tad bit wet. Also 8' beam is another want (i enjoyed the space of our old T-Craft)

    so my questions are, how to determine the proper height of my floor to keep it above the water line with say 2500# payload. Is 22' with an 8' beam appropriate or should i add some length and narrow the beam? Is the tunnel hull even worth doing since I will not be mounting the engine toward the bow, my worry was losing control during turns like the early carolina skiffs would. also, scarfing, should I drill through the areas scarfed or am I causing integrity issues by mounting the stringer on that point?

    I do appreciate all help, and appologize if I have missed a prior post that covered all of this, just havent seen much on self bailing hulls even though the concept is simple enough...both of the stapletons have this feature and i find it wonderful.
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    You need to first calculate the loaded displacement (weight) of the boat. Then you calculate the submerged volume of the hull that equals that weight in water. You also need to calculate the center of flotation and center of gravity. That will tell you where the waterline is. It is not really complicated but tedious.
     
  3. SNEAKINDEACON
    Joined: May 2014
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    Location: Tampa, FL

    SNEAKINDEACON New Member

    http://www.blueheronwings.com/bh/comps/bdesign.html

    these calculators would work for that correct? In the 1st calc I would just find the difference of 8 w / 22 long with 2" of draft vs 5" of draft? the draft dept i used were just estimates. but were actually somewhat close to 2500.
     
  4. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    A boat of those dimensions, less than L/B 3, is likely to be more than a little bit bouncy if you go at any speed. A 29 x 6 footer will have the same space and ride better, need less power for a specified speed, more economical to run, and probably not as wet. Of course it would cost a bit more for slip rental.

    Keep in mind that a boat with a sealed floor space, sufficient in volume for self bailing, will float upside down if ever capsized.

    How will you power the boat? How fast do you want to go? Is economy of operation a factor? Will you trailer the boat? Is it to be used on the flats, outside the sea buoy, etc? A fishing boat, scuba platform, pleasure cruising, gunkholeing?.......More details please.
     
  5. SNEAKINDEACON
    Joined: May 2014
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    Location: Tampa, FL

    SNEAKINDEACON New Member

    26' is my max length for the trailer, I thought of a narrower beam would reduce drag and allow me to get buy with a little less power.

    as for power, it will be an outboard, expecting about 80-100hp...thinking the 100 with a lower pitch prop since it will have a fairly heavy load and Ill need all i can get to get onto plane at times.

    itll be intercoastal and at most 1 mile offshore in the gulf...2-4' waves is about my usual environment...its just supposed to be a working boat essentially that i need a casting platform or two on. doesnt have to be fast, 20-25mph is more than enough for me.

    I've had issues without not being able to get some boats up on plane when loaded with fish and having to do 3-5 knots all the way in turning 4500rpm
     
  6. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Considering the very basic nature of your questions, it's pretty obvious, you don't have the skills necessary to design a hull. The logical choice is to buy a set of plans and many are available in this size range. Nor only do you need the hydrodynamics end squared up, particularly if you hang some serious HP on it's transom, but also the structural elements need to be able to tolerate the anticipated loading, especially when going fast. Have a look a Glen-L.com and Bateau.com for plans that might fit your requirements, remembering that you can changing styling to suit your wants and the math is already done for you, so it'll float where you paint the waterline.
     

  7. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    SneakinDeacon, Par himself is a very competent boat designer who probably has a stock plan that is worth examining. What he is saying about design and construction is the real deal. We have numerous professionals here, to their credit, most of them are very hesitant about posting self promotion stuff on the forum.
     
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