Good news (I think) is that it hardened up after 12 hours. The cracks
were two surface 'skin' cracks on the starboard rails in line with the
footstraps - seemed to be a bit soft here too when I was examining the
cracks, but it was hard to say if that was just loss of integrity from
the crack, there wasn't any big voids, so I didn't bother with filler.
The patches just went over the surface. The port side rail was always
hard, but likely I hit the chop with more impact on starboard tack. I
gently pushed on the patches this morning, I couldn't feel any obvious
voids from melted foam. Maybe I was lucky.
Yellowing is no problem on a 1990 - ish board. I was just hoping to
get another few months out of it - 2/3 of the people consulted on the
beach said "throw it out, opportunity to get a new board", the other
1/3 said "easy fix".