How to tell if a 1997 17 foot Carolina Skiff is waterlogged?

I have a 1997 17 foot Carolina Skiff and the original owner of the boat said he thought it may be water logged. I have a 2001 Yamaha 60hp 2 stroke on the boat and the thing flys, honestly with two people it tops out around 35mph. The boat seems to be good and the hull is strong but in the back of the boat their are a couple of patches on the deck where the floor seems soft but it feels like the foam under it is hard since the deck only moves a little bit up and down. How could I tell if the boats water logged and is that alright if the deck in the back in a couple of spots moves up and down a little(it does not feel like the foam is soft but that their maybe be a little air between the deck and the bottom foam?)|||If the boat was waterlogged you'd know it. It would be real sluggish at getting up on plane and wouldn't be very fast either.