Goblin ships are classed based on function and location of standard operations.  While there are designations for non-merchant ships; they are seldom, if at all, commissioned.

KMS - Kalimdor Merchant Ship (Based from Ratchet or Steamwheedle Port.)

AMS - Azeroth Merchant Ship (Based from Booty Bay.)

UMS - Undermine Merchant Ship (Based from Undermine or Bilgewater Port [Isle of Kezan].)