Floating bridge.

My sketch models made from thighs and card. 

The external skin that could work in my design needs to exert force inward on the internal structure.

And the internal needs to exert the same force, so that these forces could be balance and the structure would stay up like these.

I broke the card structure because the thigh doesn't allow enough stretch!

My sketch up of the floating bridge to show scale and roughly how it would float.