Distance between pontoons for stability

Discussion in 'Stability' started by jtmboat, Feb 24, 2009.

  1. jtmboat
    Joined: Feb 2009
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    Location: Raleigh, NC

    jtmboat Junior Member

    First posting so hopefully i have correct forum and thanks in advance for any and all help.
    I'm about to make a small poling "skiff" that is for extremely shallow waters.
    I say "skiff" but it's more like a "dock" section or pontoon as it's going to be approx. 4' x 12' and 6"-8" tall and will be poled once in the flats and tidal creeks and used to fly fish from,,,the deck will be flat. I'll add a trolling motor as well.
    I'm thinking two pontoons seperated by some distance will be much more stable than a single hull but not sure how much they need to be seperated for optimal stability. Is there an "easy" formula or rule of thumb to go by to figure out the distance the two hulls should be seperated to acquire best stability?

    To keep within my orig. plans, i could make each pontoon 7" tall x 20" wide and 12' long and seperate each hull by 8" gap/tunnel. If each hull is 7" x 20" x 12' then each would have approx. 12 cubic feet of volume and thus each should float approx. 750lbs if weight is evenly distributed.
    Is 8" gap between hulls close to being enough or do you think it'd still be wobbly for standing up?
    Ideally, i'll have a large cooler secured to the deck so i can stand on for poling or sit on as a seat when using trolling motor.

    Any ideas or thoughts on this?
    Thanks again.
  2. robherc
    Joined: Dec 2008
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    robherc Designer/Hobbyist

    the 8" gap will be better than having only a single hull, but not by much. I'd recommend upgrading it to, say, 5'x15'x8". That way you could actually give it SHALLOWER draft, while spacing your hulls a bit further apart for enhanced stability. If you make the pontoons on the raft I just mentioned 18"x15'x7" deep, you'll be displacing 13 1/8 cuft of water, for about 814lbs total. Also, you'd then have 24" spacing between the hulls for MUCH better stability.

    If you HAVE to keep it to the 4' width AND the 12' length, then I'd at least recommend going down to 18" wide hulls, and adding an inch to the depth. You'd end up with slightly more draft, but the stability increase by going up to 12" spacing would be well worth it. (though I do NOT standing on a cooler, on top of a 4' wide boat!)
  3. jtmboat
    Joined: Feb 2009
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    Location: Raleigh, NC

    jtmboat Junior Member

    thanks robherc,
    that's sort of what i was thinking. I've got some 7" x 20" floatation billets to play with and a neighbor has some of the 10" x 20" billets....i think i'll make some type of frame to set on top of the billets and figure out a set of spreaders that will allow me to vary the distance between each pontoon to see what works best,,,testing both size billets like that should give me a pretty good base to guestimate what i want to end up with.
    thanks again.
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