This exact thing happened to my 86' while sailing off Myrtle beach. It did not crack the transom, however. A hobie is rather difficult to sail with one of the rudders near horizontal. I had to accidentally gybe all the way back to the beach. It wasn't fun at all. Several of the ss screws broke off inside the hull.
I tried drilling out the screws, but that proved to be near impossible. EZ outs didn't work either. If you try to drill them out, invest in high quality cobalt left handed drill bits. That way if they grab the screw things are moving in the right direction.
I then sought the advice of others on this forum and several close friends. I ultimately came to two possibilities:
It was a given that I was going to upgrade to the one-piece gudgeons, then...
1. Cut ports in the sterns, re-drill the transom, and thru-bolt.
2. Cut out the aluminum plate, glue in a new plate, fiberglass over the new plate, drill, tap new holes, and install the new gudgeons.
I went with option 2. I just did't want to put ports in a perfectly solid hull. I did this repair in the spring and I've been sailing hard all summer with no issues. To be honest, the transom is probably more beefed up than it was from the factory. It sounds like a lot of work, and it was to an extent, but I am happy that I didn't have to through bolt and worry about potential leaks in the future. Plus, it just seemed like it would be really hard to work inside of the hull from a 4 inch opening.
So, here is the run-down of what I did. If you want more detail or would like to know where I got supplies, shoot me a pm.
1. Use a dremel to begin removing the gel, glass, and plywood from the back of the transom. Use the screw holes as an initial guide and then work your way outwards until you have the whole plate exposed. You will cut close to the outside of the hull.
2. Remove the plate. On an old boat there is likely going to be some corrosion. It will likely come out very easily. If not, take your time and try not to crack the inside glass. It is really thin.
3. Clean everything up nicely.
4. Glue in the new plate with 2 part epoxy thickened with cabosil
5. Let the glue set for at least 24 hours.
6. Fill in gaps with thickened epoxy mixed with Q cells to aid in sanding.
7. Begin to taper out the transom for new glass to adhere with a side-angle grinder.
8. Begin to lay filets of glass, starting small and building the transom back up.
9. When you feel like you've built them back, sand and fair them smooth.
10. Re-gel the transom
11. Drill new holes using the new gudgeons as a template
12. Tap the holes
13. Install the new gudgeons
14. Sail it like you stole it.
I hope this helps some. I was really intimidated by this repair and it took a couple of years before I felt like I knew enough about what I was doing. I had never done a major repair before on the boat or laid fiberglass. I simply didn't have the funds to take it to a boat shop, so I had to do it on my own. To be honest though, it wasn't nearly as difficult a repair as I thought it would be.
If you get in there though and start to see real structural problems, you may want to seek the advice and/or repair from a pro.
Here are some pics of my hulls and the process. I stopped taking photos after laying the glass. I think I just got a little antsy to get to the water. I ended up going with regular old white gel coat. It's an old junkyard boat so I didn't really care about the cosmetics. To be honest though, it looks kind of cool with the white transoms I think. http://s1319.photobucket.com/user/jsaut ... t=2&page=1
Pics would be helpful.