Full disclosure, I'm cribbing heavily from Marcus Rediker's Slave Ship here.

Work on a slave ship was actually a pretty crappy job, as far as positions aboard ships sailing the Atlantic went. Considering the amount of time spend in and around Africa and the Caribbean, the climate was miserable and dangerous; fever was a constant threat to Europeans who spent time in the tropics. Disease ran rampant aboard slave ships, and it was obvious that the ship's human cargo would kill any member of the crew they got their hands on (a fairly rare occurrence) As icing on the cake, crewmen aboard slavers had to employ violence at a frequent rate to keep the white crew alive and safe. This stretched as far as throwing people overboard if food or supplies ran low.

Because slaveships were a miserable place to work, only the most poor and desperate tended to apply as crewmen. Few spent their careers entirely on slaveships, as they would happily take other jobs as they came along.

Masters of slaving vessels were notorious for their cruelty, Floggings were frequently performed on both white and black people to encourage discipline and good order. Another reason for ship masters' cruelty was likely the stress they were under from their ship's owners. Rediker likened ship masters to foremen: middlemen responsible for earning profits for and enforcing the will of distant proprietors that had neither the time nor the inclination to closely observe the trade in human lives their business rested upon.

Hope this helps!