We built an 8x10 floating dock using 6 plastic barrels. Because we squeezed 6 barrels in we have some running parallel with the boards and others running perpendicular. The ones running parallel have 1 very "soft" board (from the roughly 35" of no support) and 1 board that pops up a 1/2' or so from the barrel pushing on it. Functionally I think the dock is fine, but the aesthetics are driving me nuts. Any bandaids I could put on the bulging board to bring it down? We used Trex wood if that has any impact.
You could spread those upward forces out and significantly reduce the bulging board if you can use a few 5/4 boards that would be installed perpendicular to the decking, beneath the decking, and above the barrel. Secure this (or these) new boards to the decking on either side of the bulging deck board and then secure the bulging deck board to the new board/s. This will likely require that the bulging deck board be removed and the barrel be pushed downward to insert the new boards.
The above is a Band-Aid for sure, but would spread the upward force of the barrel out over the adjacent deck boards. The 1/2" pop-up would disappear, but might cause the adjacent boards to rise somewhat creating a gradual hump.
To do this properly would be to add bracing between the deck joists that go over the barrel and keep it from even contacting the deck boards. This would be a bit more work, but would eliminate the new 5/4 boards and deck boards from being sandwiched together where rot would be prone to develop.
Engineered wood used for decking really needs to be supported on 12" spaced joists to prevent sagging over the years. What you are seeing is the sag but in reverse and at a faster rate because of the increased span.
