Here is your starting point (FAQ Forum):
http://www.hobiecat.com/forums/viewtopic.php?f=18&t=1156This is a hugely discussed topic, so if you do a search, you will find tons of info on this subject.
The general repair process for small areas is to drill a series of holes through the outer skin and into the foam core, but not through the inside skin (use a depth gauge on your drill). Then use a syringe filled with epoxy to inject resin into the soft area. Once the resin hardens, the hull should be solid.
For larger areas, or areas that are saturated with water, you will likely need to cut out the existing core and re-build the laminate. For older boats if there are large areas of delamination, it generally isn't worth attempting to repair and the boat should probably just be parted out and the hulls scrapped. The problem is that once delam starts, if you don't repair it soon enough, the entire hull will go soft and eventually fail. Hobie 14s and 16s generally develop soft spots just in front of the forward pylons. This is a structurally critical area of the hull and if you sail the boat in this condition, it is very possible that the entire bow will snap off.
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