Best cuts for pontoon decking

Discussion in 'Multihulls' started by Carlazzomark, Jun 30, 2013.

  1. Carlazzomark
    Joined: Oct 2006
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    Location: Michigan

    Carlazzomark Senior Member

    What are the best cuts and placement for a marine plywood deck on a pontoon boat, assuming I want a platform over 8' wide, and sheets are only 8'?

    What are the issues of strength and support of the boat?

  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    You'll need to offer some more information about what you're trying to do and on what, for any reasonable answer.

    Most pontoon boats have an athwart support system of some sort, such as extruded or stamped sections, tieing the two hulls together. The decking is fastened to these typically.

    Making longer than 8' plywood sheets can be handled a few different ways. You can double plank, which is the easiest, but requires twice the number of sheets, though these will be half the needed thickness. You can scarf them, butt block them or use the Payson butt joint too.

    I'm a big fan of double planking, especially if you're not going to use a true marine grade of plywood. For example, if you want a 3/4" plywood deck, you apply two layers of 3/8" plywood, staggering the seams, all glued and screw together. The result is a 3/4" thick deck, as big as you want, with no seams, essentially becoming a homogenous and contiguous plywood deck. It costs a little more to do it this way, but this has many benefits, such as no seams to leak and if the seams are well staggered, stronger than a single 3/4" deck and it's really easy to do, compared to a scarf or Payson butt joint.
  3. Carlazzomark
    Joined: Oct 2006
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    Carlazzomark Senior Member

    Sorry. To better explain, I will be making a pontoon boat 24' x 8.5', with aluminum cross members every 16'-18" which tie the pontoons together, and marine grade plywood attached to them by bolts.

    I will be doing this in Italy with no special wood joining tools.
  4. Petros
    Joined: Oct 2007
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    Petros Senior Member

    how far apart are cross members, 16 feet? or 16 inches? is that 16 to 18 inches? If so than that means the plywood is spanning at most 18" between the supporting members?

    You can use 1/2 marine plywood with the face grain running perpendicular to the supporting cross beams, always have the joints in the plywood end over a cross member with both edges of the plywood deck attached to the cross beams. I would attach the plywood to the beams with screws at about 6" spacing.

    the plywood edges running perpendicular to the supporting beams can be left unsupported if you do not mind some slight differential deflection when someone steps right on the joint (and one side is loaded more than the other). If not you can use strips of plywood under the floor about3 to 4 inches wide that straddles the joint, with wood screws that go down through each edge of the plywood deck into the wood strip below. Adding adhesive to this joint will prevent moisture from being trapped in the joint.

    good luck.

  5. proagenesis
    Joined: Jun 2013
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    Location: european union

    proagenesis Junior Member

    the easiest way to ....

    hello ....

    I am just amazed .... not to find any one here to just recommend using >
    two component epoxy glue >

    and then > maybe covering the whole deck with some glass and epoxy filler !
    maybe under neat just epoxy .... and just the joints reinforced with some glass >

    the joints resulting > will be stronger then the ply itself !

    this will make a deck to last longer > and will be a lot easier on you to construct
    just look for a dealer of composit materials > and talk to him ....

    you still can use ....some screws to fasten the deck to the aluminum support
    just making sure to using some sealer > so the ply will not get water logged

    regards proagenesis

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