Aeration (pardon earlier spelling) could initiate at any point along length of fin totally dependant on route and where air is originating from.. Suspect its nearer base ???(ie its nearer surface) but this is only one aspect likely to cause spin out ; and the reason I mentioned it was to clear up the misuse of the term cavitation.. (Which IMO simply never happens on any wind driven craft.;Hydroptere whose fins and foils must operate at significantly higher pressure differentials than WS does not cavitate.) I`ve seen cavitation damage on stainless steel surface piuercing props; never seen anythiing similar on WS fins.. (spoken to a few who insist they`ve seen it tho ???)
A fin aerating is only one reason fins release but it is hard to seperate aeration from simple overloading or too high A0A.. Suspect in WS its probably a combination of all 3 to some extent.
ie) Any fin will spin out
a)if aerated. (chop; leaving water etc etc)
b ) if overloaded ,that is more load put into it than it can handle
c) if expected to operate at too high(or low? ) AoA (angle of attack) that is sailed too close to wind.
Fin design;shape; cord; thickness..will all effect when above will happen.