I don't have any experience on ships. I don't know what O.S. or an A.B is.
That would be an Ordinary Seaman or the next step up, the Able Bodied Seaman.
Unless you get very lucky, I don't think you are likely to find someone small going your way. The better bet would be larger ships. Look for a ship that engages in the tramp trade and is going in the right direction. Speak with the ship's Master and ask how you might pay your way or otherwise earn your keep.
This could be a wild goose chase. Good luck.
T. P. Donnelly
S/V Tranquility Base
1984 Islander 30 Bahama