If you were actually tacking (ie going thru head-to-wind) then it's really odd that there was enough shock loading on the boom to do this damage (barring a weakening of the boom).
However if you were gybing from beam to beam then in fact the loading could be significant if not controlled.
I wonder if in fact the loose footed sail is a large factor - I'd like to know if anyone ever actually analyzed the boom loading of loose footed vs bolt rope mains.... The major loads will be on the clew and tack in any case, I suspect. Esp with the outhaul eased I wouldn't expect the bolt rope to really spread and absorb a lot of load. But who knows......
...And I've only just had the bolt-rope cut out of our mailsail to make it loose-footed!! With mid-boom sheeting, I, for one would REALLY
like to know before I go out again.
Which begs the question: I must have seen hundreds of different arrangements over the years, but does anyone know the "optimal" ("best") way of attaching main sheet blocks to the boom in a mid-boom sheeting set-up??