Hollow Hull. Is this normal?

Hi,

Today I made two hole on my Centurion Avalanche 2004 in the V-drive Area. One 2inch for the Depth finder and another for the ballast intake.

I was sure hulls were one solid piece of fiberglass, but apparently it's not the case on my boat. It's the first time I'm piercing a hull so I really didn't know what to expect.

From the outside, there is the gelcoat, 1/2 inch fiberglass, then hollow for maybe 1/4 inch , and then 1/3 inch fiberglass. Is this normal?

Also, on the side where i made a one inch hole for the ballast intake, everything was dry. This was not the case for the hole I made on the bottom besides the speed sensor. It used to be the bottom drain plug which i removed to replace it by the thru hull depth finder. It kept pouring water and it's all wet.

Again, should i be worried?

Thanks!!