The game is essentially broken with two players, because the
luck of the draw combined with only one action per turn can get a
player into a sitation where they have an imbalance between the
merchant ships and the pirate ships. Either you can attack or sail,
but not really both effectively once your hand balance goes over too
much in either direction. In the beginning, you can try to keep your
hand managed but once you draw a few too many of one kind, it can be
nearly impossible to recover.
One strategy I tried was to draw a lot of cards early in the game, but
once your opponent starts sailing merchant ships then you are forced
to attack them at some point.
By example, in one game, I won 75 to 25 and in the second game I lost
81 to 19. Both very lopsided scores, to say the least.
That being said, the game is still fun and it plays quickly enough,
but with two players it just isn't the same game as it is with three