Hi Ramona,
Shoalhaven Inlet is the body of water between Shoalhaven Heads and Comerong Island. It used to be the entrance to the Shaolhaven River but closed off to the sea now due to the river diverting along Berry's Canal. If the Shaolhaven River floods the Council digs a channel through the sand blocking the entrance to assist water exiting the Shaolhaven.
My guess is the snake has come from Comerong Island. I have been told by the locals that snakes swimming about are quite common here. First time they have heard of a Snake making its home on board a boat. One benefit is he probably kept the birds off the boat.
Here is the snake skin that alerted me to his presence.