Tom Haberman's reply to my request for advice essentially confirmed most of what was posted here. He also prefers the inner skin patch followed by the lamination of the same epoxy/glass/foam sandwich (vacuum bagged), so that is the way we will try. Thanks guys!
I will do my best to photograph and post the repair progress.

Mr. Haberman was surprised that the composite did not show signs of weakening and failed without warning, but he didn't see the pictures from before the re-coat job. The weakening was visible, I saw it and just failed to act accordingly. My only excuses are that I didn't know Supercat 15 hulls were glass/foam composite and that I trusted the advice of a shipyard owner who, in turn, has no experience with composites and also did not know the hull was composite.

Besides, I might have understated how hard we were sailing the boat. The total crew weight was over 200 kg (over 440 lb) and the wind was blowing about 30 knots, with stronger irregular gusts, as is common in small inland lakes.

The pitchpole was preceded by three or four bow buries and happened on our way to the finish line, while pushing the boat hard to recover from a couple of horrible tacks that had cost us the first place. It was the first time on a beach cat for the crew (the shipyard owner). The finish line was in front of the club instead of downwind.

(digression: we do this when there are spectators like press or sponsors, so they can see the finish and take pictures. You don't want them in the water when it is blowing. end of digression)

So, we would point higher in the lulls and bear away in the gusts. Worked fine until a stronger gust caught us in the famous death zone. An older SC15 competitor said that I should have dumped, pinched and capsized, as he did. It cost him the race just like ours, but the capsize did not cause any damage at all.

Cheers,

So what is the latest with the repairs?

This is a spare time job for the shipyard and the owner has to supervise it personally. Also, I want to be present during the critical parts.

We waited a lot for the epoxy and pvc foam, barely started with the repair and then I travelled. When I returned the shipyard owner travelled. Work will resume when he comes back.

I'll keep the thread updated.
Thanks for the interest!

After almost five months in the shipyard and one month waiting for me to rig it, the SC15 was officially re-launched last sunday. The glass/foam/gelcoat job looks impecable, with a mirror-like finish. My daughter had to ask what side broke for she couldn't find it simply looking and feeling.

Unfortunately I have no pictures. The last months were very busy and I could only visit the boat twice and didn't have a camera with me.

Still, AFAIK it was fixed using the drawings I made based on the instructions and techniques received here and from Tom Haberman - many thanks to all of you!

I tried to post the drawing and instructions here but (for obvious reasons) they are in Spanish and the max size makes the image fuzzy. Anyway, it gives an idea of what to do and anyone interested can get the uncompressed file from me.

Very Cool!