It doesn't look like anything other than the underside of the polygons. I was tumbling though, so it was hard to get a good look. It certainly didn't look like "underwater", but it acted like it. The PT's bouancy kept pushing it to the surface where it would get knoked under by the CV again.
The initial impact was neat as I watched the bow of the PT get pushed under, and as my view point was still above the surface it looked ok, but bad in a "oh crap" fashion.
Another change I noticed was that the main guns on the CA are now aimed from the gunnery nest and not from the turret. Much better.