I have visited Bruges from Zeebrugge, it was a 10-15 minute journey and a coach journey that was provided by the cruise line and a minimum cost.
Suggest you go to ports of call on cruise critic for lots of useful informatio.
Cunard charge $59 a head for a rtn bus ride about £110 for a 10 mile trip for 4 i would get the train or a taxi .
Emailed firstname.lastname@example.org and got info about reserving a taxi from the Dock at Zeebruge to city center in Brugge. It is €45 each way and you can make a reservation for it by sending a credit card number to hold he reservation. Payment is made to the driver with a credit card or euros. The taxi is for 2 or 5 persons so sharing it would be much less than the bus offered by the ship. Plus the taxi drops you off in the city center where the bus or taking the train drops you outside the city. Alternatively the trains don't run from Zeebruge station on the weekends, so if you go to the Belgium rail site it will not show trains from Zeebruge.
The trains were every 40 minutes on the weekend from Blankenberge.