The search function would have yielded the answer for the last two posters.
The classing recommendation is also for hero sailors. Why? Because with each classing beyond fighter (at lvl 40), your crew growth will not increase (as is the case for all other sailor types), but DECREASE (fighter +5, ace +4, sqd ldr +3 crew per level). So even if your displayed ability bonus goes up with further classings, the total ability - displayed ability multiplied by (vets + experts) - will only increase more slowly, depending on the number of vets you have.
So be sure never to class sqd ldr. Whether to class ace or not, see above (no. of vets).