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]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "dockage":
   admission, admission fee, anchorage, anchorage ground, basin,
   berth, breakwater, brokerage, bulkhead, carfare, cellarage, charge,
   charges, cover charge, demand, dock, dockyard, dry dock, dues,
   embankment, entrance fee, exaction, exactment, fare, fee, groin,
   harbor, harborage, haven, hire, jetty, jutty, landing,
   landing place, landing stage, license fee, marina, mole, moorings,
   pier, pilotage, port, portage, protected anchorage, quay, road,
   roads, roadstead, salvage, scot, scot and lot, seaport, seawall,
   shipyard, shot, slip, storage, toll, towage, wharf, wharfage