Yeah I am one of those 1/72nders....
It was the only game in town, and even then I had to Drive up to Gig Harbor, Washington every month.
Battle for two or three hours and then drive back to Portland, Oregon.

The light ship waterline is the bottom of the black, or boot line, painted around the side of the ship.
The boot lines are typically 3/8"-1" wide. So we could easily get balsa 1 1/2 inch below the water line for the larger ships. We have only launched one battleship, the club is proposing launching up to 4 this year for testing.
It almost sounds like your ship floats at the main level of the main deck. Are you talking about the weather or main deck. If that is the case, the balsa runs down from the main deck 2 1/2 inches or more down to the fiberglass bottom.

My LST went down RC tank and all with one penetration below the waterline