Hard chine flat bottom

Discussion in 'Boat Design' started by COLD-EH', Oct 4, 2007.

  1. COLD-EH'
    Joined: Dec 2005
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    COLD-EH' Junior Member

    Hi! I am building a flat bottom boat and wondering the benifits/disadvantages and characteristics of a hard chine. The hull is 16 1/2' long, 86" wide bottom flaring at 105 degrees. The bow tapers to 5' at the 12' point from the stern. What can I expect?
     
  2. Loveofsea
    Joined: Jan 2007
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    Location: Southern California

    Loveofsea New Member

    Here is a link to a story about the flatbottom skiff that i designed and built. I have logged over 60,000nm of open ocean in this skiff since '91.

    http://www.oceanskiffjournal.com/Su...02Issue01/General/GoodSkiff/boatprofile1.aspx

    My skiff is 19ft LOA, the bottom length being 17.5ft. The bottom is 59" at the widest point, 2/3 fwd of the transom and tapers to a width of 51" at the transom. I would not recommend a 16.5' hull with a width of 86". Also, i would keep the flair to 100' to 102' max.

    What do you plan to use your skiff for and how do you plan to power it?

    Brad

    (loves the sea)
     
  3. COLD-EH'
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    COLD-EH' Junior Member

    Pretty impressive Brad! This thing is not really a skiff but an airboat. Just really wondering how this thing might handle?
     
  4. messabout
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    Location: Lakeland Fl USA

    messabout Senior Member

    Airboats in this part of the world are typically soft chine layouts. They are very wide in comparison to length, in about the same proportion that you have suggested. Airboats are inherently top heavy and the Florida boats keep well rounded chines so that the boat will skid rather than trip. If you are planning to use a powerful engine in the quest for speed, then do give some consideration to the tripping possibility. Flare in an airboat is not necessary except for the possibility of keeping the spray down. That can be accomplished with a pair of whiskers just as well. A slab sided boat is not as pretty as one with flare but a lot easier to build. If you plan to trailer the boat 105" is too wide in many US states. Best check the Alberta regulations.

    Will you be powering this boat with an aircraft engine or a big automotive V8? 350 cubic inch engines are popular herabouts. Some of them use race car engines that make upwards of 500 HP. I think those guys are out of their minds but they don't pay much attention to what I think.
     
  5. COLD-EH'
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    COLD-EH' Junior Member

    Yeah, flare is 105 degrees, width is 96" and 89" X 12' bottom. Big auto engine. Was wondering if a water rudder would reduce the trip hasard?
     
  6. Pericles
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    Pericles Senior Member

  7. rwatson
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    rwatson Senior Member

    Depends if you are sailing or powering. Flat bottom sharpies like the Norwalk Island sharpies sail well heeled over, as the flat bottom and side make a V at sailing angles.
    Powering will be fast, but in any kind of sea, it will pound a lot. Quite jarring over 15 knots
     
  8. lewisboats
    Joined: Oct 2002
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    lewisboats Obsessed Member


    no as it is the chine which will dig in regardless of the rudder. A vee bottom will bank into a turn but a flat bottom doesn't bank nearly as well, and when it starts to slide...it has the ability to catch the chine and flip...very quickly.

    Steve
     
  9. COLD-EH'
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    COLD-EH' Junior Member

    Yeah I'm getting pretty convinced i need to do something about it. The hull is .105" steel and I could cut out a wedge to soften it BUT I was looking at the hull and I think I will do an add on about 1" above the bend and make a nice glass rounded chine out of foam and glass. Positive flotation, extra bumpers and soft chine. Just bolt the side attachments on to the hull. Sound like an acceptable plan?;)
     

  10. COLD-EH'
    Joined: Dec 2005
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    Location: Edmonton, Alberta, Canada

    COLD-EH' Junior Member

    I found a video of an airboat with pretty much the same hull shape as mine. Doesn't look like it's tipping over so I'll leave it as is for now and if I don't like the way it handles at least i have a plan up my sleeves!

    http://www.southernairboat.com/photopost/showphoto.php/photo/2390/cat/526

    Here's another couple I kinda get a kick out of!

    http://www.southernairboat.com/photopost/showphoto.php/photo/1810/cat/526

    http://www.southernairboat.com/photopost/showphoto.php/photo/413/cat/526

    Thanks for the help!
     
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