The engineer's end view of te dock has the four-foot deck width measured to the centers of the pilings. This would indicate that the pilings would be "notched into" the deck, which would be an expensive way to build a dock. If the pilings are actually planned to be tangent to the deck, the effective visual width of the dock would be more like six feet, not four.

Just our opinion, but we wouldn't hire an engineer who made this many mistakes in his drawings - built to this drawing, the deck would actually be five feet wide (look in the crosshatched area) - not four feet.