The Collaborative International Dictionary of English v.0.48:

Dockage \Dock"age\, n.
   A charge for the use of a dock.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dockage
    n 1: a fee charged for a vessel to use a dock [syn: dockage,
         docking fee]
    2: landing in a harbor next to a pier where ships are loaded and
       unloaded or repaired; may have gates to let water in or out;
       "the ship arrived at the dock more than a day late" [syn:
       dock, dockage, docking facility]
    3: the act of securing an arriving vessel with ropes [syn:
       docking, moorage, dockage, tying up]