In Belfast, the queue for the shuttle was very long so we took a taxi with another couple for 20 euros (fixed price). We were dropped at the City Hall. We asked the driver for a card to call for a return trip. This was on a meter and was 10 euros!
There is a service bus which stops just outside the dock gates - quite a few people used that.
If anyone is interested, The Duke of York pub is very interesting and worth a visit!!