Staff

A Second Mate is a position held by a member of a crew. He is the second highest ranked officer on a crew outside the captain, the first being the First Mate. Typically, it was not essential to have a second mate on a ship, however captains of larger ships and crews may recruit one to have a stronger grip on his crew. On the crew he answers only to the Captain and the First Mate.

The second mate's duty is similar to the first mate and often he will share the jobs at hand between him and the First Mate. He is the next in line to take over as captain after the First Mate. This role is generally considered a "made-up" role, though it is sometimes used in fiction and by non-commerical/military persons.

One Piece
Cabaji is the second mate on Buggy's crew. Oddly enough, he seems to pull more favour with the captain and pull more weight with the crew then Mohji his First Mate. Pearl from Don Krieg's crew is also his second mate.