dredging machine

from The Collaborative International Dictionary of English v.0.48

Dredge \Dredge\ (dr[e^]j), v. t. [imp. & p. p. {Dredged}
   (dr[e^]jd); p. pr. & vb. n. {Dredging}.]
   To catch or gather with a dredge; to deepen with a dredging
   machine. --R. Carew.
   [1913 Webster]

   {Dredging machine}, a machine (commonly on a boat) used to
      scoop up mud, gravel, or obstructions from the bottom of
      rivers, docks, etc., so as to deepen them.
      [1913 Webster]