Hmmm, this is very intersting! It would be great to have tide's in the game.
However, in SS06 we do have a kind of tide, only the water doesn't go up and down. But we do have up-stream and down-stream. That's nice for starters. Let's just hope, the dev's can work out a "working" tide, with high and low water, accordingly changing streams, etc.
And yes, a depth-sounder would be nice to have in that case, since a run aground with the Titanic @ Phi Phi-islands....