A cabin boy has 33% chance to hit, which goes up to 56% with a re-roll. A hunter has 50% chance, which goes up to 75% with a re-roll, and 87.5% with two re-rolls.

So, for an expected outcome of one hit per boat, you would need three cabin boys, two cabin boys and a craftsman, or two hunters. For a greater chance than that, try two hunters and a craftsman or three hunters (expected 150%).

As your captain, uniquely, has the ability to take levels and skills in each class, he can be ultimately flexible in a fight, albeit game over if he falls. It's easier to hire level 10 hunters than it is to build your Captain to level 10, so I suggest starting him with Sailor and Scientist to begin with (using the Smart trait.) Use the re-rolls by default to maximise offense and swap to healing when necessary. Getting him the Whaler Man and Field Medic skills eventually will give him excellent passive team skills during fights.

Or you might be better off leaving the heavy lifting to the crew for the most part. Your captain does not get morale from killing enemies - whereas your crew does.