Here is a project we did about month ago. The homeowner tore out the original dock and we came in to replace it. The original dock was rotted and heaving up from the frost. We augured new 18" x 42" post hole footings dropped a cement cookie base for the support post and back filled the 4x4s. The dock is a 100' long and 7' width through most of the dock with couple of flair outs at each end. The original decking was running the opposite way we installed the new deck boards, which made a nice design feature with a center seam board every 12'. Running the decking this way also looked better from the view of the house by not seeing the seams of the deck boards butting up to each other. This is the standard way most deck boards run parallel to the long side of the home.
Posts set and working on the framing The outside of the dock is supported by the new post hole footings
and the 4x4s, the inside of the deck is built on top of the steel break wall
Here you can see the 12' sections with the seam boards running the opposite way
All the decking was screwed down with 3" exterior screws
The dock is all select cut treated pine- 2x6 framing and 2x6 decking