In my humble opinion there are too many bonuses for water movement.Currently I am playing in Modern era, and my ships have 6 standard bonus movement, meaning battleships can move 12 tiles per turn, destroyers 14.And new units will have abilities to move even more, which is kinda ridiculous.In essence it means water units can move in one turn to another continent and even more.At the same time comparable air units like bombers and P59 fighters have 8 range.Soon I'll discover jet fighters, and they will have 10 range, and in real world they are about 20-40 times faster then ships.