The tips screen suggests there is a variety of ways of hiring crew from port, but the only one I've found is visiting the pub. You can hire cabin boys or someone with a professional skill; sailors, hunters, craftsmen or men of science. Each professional has a level (1-10) and you can hire up to your prestige rating in total class levels. Initially that is 4. The higher the rating of the pub, the higher the maximum level of professionals available. Firing a crew member costs you one prestige, but it is sometimes necessary to make space for someone better or with a skill that has become important. If you can earn prestige quickly enough, you can hire level 10 crew that can make surviving battles a lot easier.