Donnie,
This plan means that you will be installing some sort of subsoil bearing foundation very close to the water's edge. This part of the project may dwarf the cantilever portion in engineering needs. I have to assume that the soils you will be penetrating to establish a suitable foundation will be wet. You may be going down pretty far to get to stable subsoil. The upside is that, depending on the size of the proposed structure, you may be able to minimize the amount of required foundation piers by making them stout and reinforced. Then, the lack of foundation members can be spanned above grade with suitably "beefed up" framing.