The "crunching" noise is the damaged foam making noise. My one hull was solid, until I stepped on it and heard a big crunch. -Then it was soft.

I've had to repair both my hulls. I used the 'On the Wire'/Beachcombers method. My first delamination was 26" long in front of the pylon. It took a pint of epoxy to fill the void. Your "four feet" sounds big. You might want to consider repairing it in two or more stages, starting with the lowest(to gravity) section first. My repair had some problems with epoxy flowing out the lowest holes, until the cure was well under way.

I fixed my first hull, then the next year I had to do the second hull. During the second repair, I noticed the first repair needed some additional repair. This is probably due to the nature of the repair being a quick and cheap fix. You live with your choices, and I've been satisified. Its a cheap way to keep an old Hobie going.

Its important to do SOMETHING before you have a structural failure. Warning: the repair can be messy so don't get discouraged if it happens, just keep going at the repair. And don't get comcerned, if you don't follow the exact details of the repair methods. Just get the voids filled with epoxy.