Soft Hull Repair

I bought my 1976 Hobie 16 last summer and got a season's sailing out of it. I stored it outside under a tarp an it got the full force of our mid-Atlantic, Maryland winter. I just pulled it out yesterday and noticed the glass on one hull was very soft; if I press with medium force with two fingers the hull side will indent about 1/2 - 3/4 of an inch and this occurs for nearly the entire length of the starboard hull. I'm guessing some rotting is happening on the inside, since the glass and gelcoat all look fine from the outside.

Has anyone had experience with this in their hulls? What is the best approach for this type of deterioration? What is it that is rotting/breaking down that is causing this flimsiness and how do I fix it?

Thanks for the advice.

Scratch the repair idea; found some decent hulls nearby for pennies. I'll just be switching those out. Be sailing again in no time!

I was going to say . . .

That hull's dead. It just doesn't know it yet.