Triple pontoons?

Discussion in 'Boat Design' started by ddrdan, Jul 15, 2010.

  1. ddrdan
    Joined: Mar 2009
    Posts: 67
    Likes: 2, Points: 0, Legacy Rep: 37
    Location: Raleigh NC

    ddrdan Junior Member

    I've started building a 20' x 8'-5" houseboat on 2 pontoons. 25" x 25" x 20' square pontoons. I'd like to add a pontoon in the middle to gain a higher weight capacity.

    The current design has the deck framing integrated into the outer pontoons. Much like a catamaran with thru hull connections.

    I was thinking of a 12" x 20" x 16' pontoon centered under the deck framing. The center pontoon will attach to the framing 5" below the top of the outer pontoons. Thus the 20" depth to match the base of the outer pontoons.

    Is there any advantage to making the center pontoon deeper, or shallower than 20"?

    What adverse effects will a center pontoon have in the way of stability?

    Thanks,
    Dan
     
  2. Deadeye
    Joined: Jan 2009
    Posts: 49
    Likes: 2, Points: 8, Legacy Rep: 20
    Location: BC, Canada

    Deadeye Bender of Nails

    I've been wondering that myself and I'd like to share a couple of perceptions I have so you folks can either confirm or quash them for me:

    1) One problem seems to me to be wave motion and comfort - it seems that as a wave passes under a 'normal' two-pontoon boat, the wave would pass under one pontoon, then the center 'space', then the other pontoon.
    With a center pontoon, there would be a point where most of the boat is being supported on the windward and center pontoons, then as the wave travelled under the boat, the boat would rotate around the center pontoon onto the center and leeward ones. This seems like it would give a 'snap' to the boat's motion that would quickly get annoying.

    2) The center pontoon would need to have the same draft as the outers, otherwise the boat would be trying to float on the center and leeward pontoons (like a trimaran). Plus it would make beaching and trailering easier...

    Like I said, I don't know if my thoughts are accurate or not, it seems intuitive but that's never a guarantee !! :?: :) :?:
     
  3. ddrdan
    Joined: Mar 2009
    Posts: 67
    Likes: 2, Points: 0, Legacy Rep: 37
    Location: Raleigh NC

    ddrdan Junior Member

    I was thinking if I placed the bottom of the center pontoon to just below the draft line on the outer pontoons, I'd have the additional displacement when I came close to max draft?

    I want it if I decide to add one or two passengers on backwater day trips.

    With that vertical gap would it ride better in the wave condition you explained?

    This boat won't see many severe wave conditions. It's a floating hotel I'm building to dock my flats boat too at night. More time on the water means more fishing!!!!:)

    [​IMG][​IMG]
     
  4. Deadeye
    Joined: Jan 2009
    Posts: 49
    Likes: 2, Points: 8, Legacy Rep: 20
    Location: BC, Canada

    Deadeye Bender of Nails

    Personally I think there's a wide gap between "won't see many severe weather conditions" and "preparing for the worst"

    Your first drawing shows that the center pontoon is actually shallower than the outers because the 5" drop on the center pontoon doesn't seem to be included.

    If it were my own project, I think I'd look at providing reserve bouyancy by enlarging the two outer pontoons rather than adding a third - but don't take my comments as anything resembling design expertise.

    How are you looking to power it ?
     
  5. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 110, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    The surface area will be higher with 3 floats than with 2 fatter floats , costing fuel at low speeds.

    FF
     

  6. ddrdan
    Joined: Mar 2009
    Posts: 67
    Likes: 2, Points: 0, Legacy Rep: 37
    Location: Raleigh NC

    ddrdan Junior Member

    Thanks for the input from all.

    I guess I'm SOL.:) The outer pontoons are already built.

    I'm powering it with a 25HP outboard.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.