I need a structural engineer. For decking calculations

Hi, I want to build a cantilever deck/ or minimal end supported deck, that will be at the end of a garden, oversailing a river wall. Connected to the deck will be a 7.5m bridge, leading to a pontoon for mooring a boat. The river is tidal. The pontoon will be held in place by a deep river pile. I have a few ideas, but would like some professional advice, and calculations to submit to the relevant authorities.