...with the alarm set to 100 fathoms... (grin)

OK, here's my best guess as to the primary contributing factors, aside from the likelihood of the cumulative effects of fatigue:

First, these 'navigators' on these boats are really much more playing the role of Weather Routers, and Tacticians... And this fleet is racing in such close proximity to each other, I think it could be very easy for these guys to become overly preoccupied with tactics, at the expense of basic navigation...

Also, this might have been an example of a sort of 'Follow the Leader' mentality at play... One of the things that has distinguished this running of the VOR, is the tendency of the pack to stick together. They're all transmitting AIS, with a range limited to about 6 miles, and there seems to be a real reluctance on the part of all the competitors to let anyone 'get away', or take a real flyer.... It's really not all that far from a group Match Race across oceans... All the other boats had passed safely past that reef and islands, and VESTAS was trailing them on just a slightly different track - could have been something akin to a race driver following the guy in front too deeply into a corner, instead of using his own braking point?