I know the sides are cored w/ balsa . What about the bottom in back by the motors? What to put a depth gauge in.

Unlikely the bottom is cored unless purpose-built race boat...

I have a 1984 chris cat and the bottom is cored and is about 2 inches thick in the last 2 feet

All Chris-Cats had fully-cored construction, including the bottoms. 1984 and early 85's were cored with Balsa, from mid-1985 on they were cored with Divinycell. I owned and raced one in Pro-Stock class for many seasons. GREAT rough water boat, not as fast as a Skater but untouchable in really snotty water.

Tom
Total Marine

Thanks for the response The boat needs a depth sounder installed and just wanted to know what is there.