If you want a ship simulation of diving in a sub, as DIAMANT said, try the Silent Hunter series.
Or you could use Virtual sailor, I think there is a titanic wreck scenery for it also..
I just don't think any sub or underwater feature will go well in SS, as it is, SS requires good PC specs, with the likelyhood of more features and a better wave spectrum in SS10 which most likely means a higher minimum PC specifications, and well, adding a underwater seabed fully textured will require an even higher min PC spec.