An interesting detail is that beyond 10 km you can't see the overturned F12 anymore even when standing straight up and the water surface is flat with a cristal clear sky. That is due to the round shape of the earth. The overturned craft will then be hidden by the horizon.

So any boat that can get away from you by that distance in a short time (15 knots => 21 minutes) is dangerous.

Wouter

Wouter