A.Mike Shannahan, a master carpenter in La Porte, Texas, responds: Plywood would not be my choice for the decking; even treated plywood can have problems with delamination when used in the open on a project like the one you describe. Plywood would also be at a disadvantage in the harsh wind and high water conditions that occur during tropical storms and hurricanes: The "lift" on 4x8 sheets could wreak havoc on framing connections and bearing members when wind and wave action team up on your dock.
I would use 2x6 or 2x8 decking of pressure-treated Southern Pine (.60-retention) nailed in place with 20-penny hot-dipped-galvanized spikes. Space the deck boards 3/4 inch to 1 inch apart to allow plenty of room for movement and for water to flow through during storm tides. All heavy members below the deck — cross ties, stringers, joists, and so...
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