The Collaborative International Dictionary of English v.0.48:

Roustabout \Roust"a*bout`\, n. [Etymol. uncertain.]
   A laborer, especially a deck hand, on a river steamboat, who
   moves the cargo, loads and unloads wood, and the like; in an
   opprobrious sense, a shiftless vagrant who lives by chance
   jobs. [Western U.S.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

roustabout
    n 1: a member of a ship's crew who performs manual labor [syn:
         deckhand, roustabout]