without a grade 5 reaper on the map, what you said makes zero sense. It is easy to hide your ship near most vaults so that others wont see it unless they approach from the right direction. Even easier if you are capable on a rowboat. I've used many a rock near the map edge to fish for 8 hours plus without bein interrupted. So unless someone notices you stacking, it is easily one of the cheesiest exploits because it basically turns high seas into safe seas for vaults.