How much water can the foam hold ?

I removed all the hardware, the splash rail, and the old paint before I weighed my (new to me) 1965 boat. I was shocked to find it at 145 pounds! The mast hole doesn’t leak and it’s been stored on a trailer in a field for years In the hot sun. Am I missing something ?

p.s. I’m making a kick up rudder from scrap wood and figure it will cost about $15. If it works as planned, I’ll post it.