Deck Rating AB or OS

Deck Rating AB or OS. You need an AB or OS to work as deckhand on seagoing vessels greater than 100 GRT.

In conclusion the OS is an entry level apprentice rating. While the AB is a journeyman rating. In contrast, holding a Master or Mate does not qualify you as an AB. Your MMC must say AB to work as a deckhand on seagoing vessels 100 GRT and greater. The biggest mistake that a mariner can make is NOT getting an AB. The result being that too many career opportunities are missed without it.