I read a book recently on the history of the East India Company, and in particular its ships.
The ships had a captain, but then 1st mate, 2nd mate, 3rd mate and so-on.
It seemed necessary if breaking into the job, to effectively buy your way with a combination of passage and training into 5th or 6th mate, and generally each voyage (a voyage typically taking 2-3 years) you had a chance of climbing the ladder one rung. At about 3rd mate, the income started to catch up on the training debt, 2nd mates actually had spare money, and a captain needed 2-3 voyages (i.e. 6-10 years) to then retire comfortable for the rest of their lives.
Other specialist jobs (carpenters, traders, and so-on) had their own separate career structures, were cheaper to get into, but the rewards were lower as well.
Nothing like modern aviation at-all really
In the modern merchant navy, incidentally, I think it's a requirement - and has been for most of a century, that to fill a command position, you have to be qualified to do the job above you. So, a first mate has to hold a masters certificate, for example.
G