De acordo com o dicionário Michaelis docas = docks

Veja o que diz o Webster's:

dock1 (dak)
n.
1 a large structure or excavated basin for receiving ships, equipped with gates to keep water in or out
2 a landing pier; wharf
3 the area of water between two landing piers
4 a platform at which trucks or freight cars are loaded and unloaded
5 a building, platform, or area for servicing aircraft
vt.
1 to bring or pilot (a ship) to or into a dock and moor it
2 to join (vehicles) together in outer space
vi.
1 to come to or into a dock and moor
2 to join up with another vehicle in outer space

Etymology
[orig., mud channel made by a vessel's bottom at low tide: hence, dock < MDu docke, channel < It doccia, conduit, canal: see douche]

(C)1995 Zane Publishing, Inc. (C)1994, 1991, 1988 Simon & Schuster, Inc.

Compare com a definição do Aurelio:

doca1
[Do ingl. dock.]
S. f.
1. Parte de um porto onde atracam os navios para carga e descarga.
2. Dique para construção ou reparo de navios.
3. Armazém de entreposto, para o comércio marítimo.