I saw a thread a couple of years ago in which someone showed the process of how they repaired a massive whole to the hull during a race series at the dock.
You will need a dry towell, high quality packing tape, some cardboard, and a sharp knife.
1. Dry the hull all around the hole.
2. Seal the hole with packing tape. Overlap the packing tape at least a couple inches out on to the good part of the hull. As you apply the packing tape, carefully cut the ends of each piece. Do not tear the ends and do not allow any wrinkles at the edges. Water will get under wrinkles and lift the tape off the hull.
3. Make a piece of cardboard that is as large as the outer edge of the packing tape. Restated, make a cardboard cover that extends to the edges of the tape applied in number 2
4. Cover both sides of the cardboard with packing tape. This will make your repair stiff. Extra layers of packing tape on the inside of the cardboard will significantly add to the stiffness of your final repair.
5. Tape the cardboard over the previous layers and extend the packing tape well beyond the repair. If you can find some of the high dollar aluminum water sealing tape with the thick butyl style adhesive, use it for the outside layer over and beyond the packing tape.
The aluminum stuff is on the shelves at the Home Depot in Austin. We used some three months ago to repair a boat we will not be repairing in the shop until October and the boat has been sailing almost every weekend with the aluminum tape as the surface...No leaks so far.
Note about the aluminum tape: It is not strong like packing tape. We did not use it for structure. We only used the aluminum tape to cover and seal our packing tape structural repair.
use hint: The aluminum stuff comes with a peel away paper backing. We let the paper tail dangle and eventually it swung around and got stuck on some freshly uncovered tape. We had to throw away a couple feet of the expensive tape because the paper only releases one time from the glue.
Also, the glue is super sticky. Wherever it touches first is where it will stay.
I remember that someone at the British Virgin Islands made such a big repair. I can't find that thread/post at TLF in the moment. Perhaps "bviemma" does remember who did that, write her a PM.
I have an old hull I'm saving for parts. I can cut you a patch from that, assuming you need more than a 2"x2" little patch. The BVI article patch was about 12x12" as I recall.
Then you epoxy on flanges on the edge of the cut hole, and drop the patch onto the flanges. Then fill, fair, paint etc.
Or, try your homeowners insurance, and maybe you can get a Pro to do it. It's pretty common for them.
Yes, the one I was referring to was quite large. Maybe 12x18 inches. I have a pretty good recolection of the process of matching the shape on a borrowed hull, I just wanted to print it for my files.