I suggested in the past that different power levels should get different kinds of maps when they claim. Basically, there would be no limits on who you can attack. However, you would get better maps from attacking higher powers, and better maps would mean better rewards. This would encourage players to wait for stronger players to sink instead of sinking anyone, but they could also sink lower level players if they need the sailing for their assistant. This would also reduce the incentive of using alt accounts, as their sails would not be rewarding. This would also make sailing more relevant to higher powers, because 150,000 coins isn't much let's face it.