Do I understand correctly that your damage is underneath the cuddy floor? (Forward of the CB)
In that case, the solution would be to cut a generous opening in the cuddy floor (large rectangle) leaving just enough along all sides to comfortably tab the cutout back in place when done. (Closing the opening would mean glueing some strips of pre-laminated epoxy on all sides under the bits you've left over so that you get a bit of a shallow L shape. With the large opening you can easily clamp these strips. Then lay the cutout on top and glue in place. Finally fill the remaining groove, perhaps even with some high strength filler.)
If the damage is so far forward that it extends under the flotation tank at the front of the cuddy, cut a large circular hole centered in the bulkhead (sized so it can later be closed with the largest screw-in deck plate that you can source).
This would allow you to access the repair from the inside and remove any soggy foam (my suspicion is that the foam is in the tank portion only - that would be typical).
In case you are wondering, it is totally possible to make a repair from the outside only: you would lay up a "backing plate" that is a bit wider/longer than the gash, but thin enough to be flexible. You enlarge the gash by removing all torn laminate, and bevel the edges. The you reach in and rough up the inside. You insert your backing plate and glue it in place with epoxy. Slightly thickened, or use one per-formulated as a glue, like Gel-Magic from SystemThree. You can drill some holes and use screws, or even pop rivets to hold the backing plate tightly against the inside of the hull, so it conforms and helps the hull to assume a fair shape across the gash. When the glue has set, drill out the rivet (take out the screws, if you remembered to wax them beforehand).
Now you have a low spot in an otherwise fair hull: fill with layers laminate going to smaller sizes, not larger as you add layers in your stack. Fair and finish.
Even if you can access the inside, you may want to use this backing plate method, mainly to make sure the hull isn't distorted. Using fasteners to hold the backing plate is likely to give better results than pushing it from the inside (it's tough to make it lie flat -- as I experienced with a
repair that had inside access). However, getting the backing plate in place and even adding the temporary fasteners may be just a bit easier from the inside. Working from the outside, you may need a string or wire to the middle of your plate so you can pull it against the hull while working to fasten it.
You might also want to read this post: "
ten steps to adding a patch"