The official site for the Barcelona Bus is www.tmb.net where maps and prices are shown but you get more information on the US site www.viator.com where it's called the Barcelona Hop on hop off tour. You can but tickets when you board. There are 2 routes which cross at Placa de Catalunya (the start point) so you need to plan your day in advance. There is a tourist bus stop at the Maritime Museum which is near to the Columbus tower should you want to get on the tour bus asap. There is also a good metro system if you need to get around a bit quicker but beware of pickpockets (and the same goes for the Ramblas and adjoining streets where theft is a major problem)
I don't know the name of the docks but they aren't that large. A local bus service usually runs from the docks to the bottom end of the Ramblas but gets very busy particularly for the return journey in the afternoon so you may want to budget for a taxi to get back to the ship.
Some sights can't be seen from the tour bus (e.g. Parc Guell) but that's the point of a hop on/off bus. If you finally get off the bus in Placa de Catalunya you are at the top of the Ramblas. From there you can walk down to the Columbus (Colom) tower where the local port bus runs from. Hope this help.
Ive done island cruises and we went into barcelona and im sure it was called somthing towers we docked at might be wrong .
I agree with Bradley .. from the ship (if you like walking ... its not a long walk to the Columbus Coloum which is at the end of Ramblas. You could then walk up Ramblas and at the end in the square both of the Hop-on-off bus start ... near the end of Ramblas you will see a booth that sells the day tickets.
They will also provide a map so you can plan the places you want to see .. bear in mind one of the stops is Columbus Coloum .. so its a good idea to make this your last stop as it is the closest stop for the ship.
If you only have 8.30 to 3pm to see the sights suggest you go to the websites suggest by Bradley and plan your day in advance as Barcelona is a big city and has a lot to see show you ... it's a great place (well worth seeing) but be carefull with your belongings as a few light fingered people around.
Have a great time .. I will be in Barcelona in November for the third year in a row and always look forward to returning.
We took to bus all over Barcelona when we di OV cruise 2 yrs ago. We got off early 8am and walked up Las Ramblas, but nothing was open. We stopped for loads of coffees as it was so hot as it approached mid day. The buses are brilliant you get on and off, the we did the full tour doing gothic part taking us back to top of Las Ramblas, and walked back to ship, we were in the berth at side of terminal building, so it was quick getting back on. The queues at the stops were very long, so we used to walk on a bit and join a shorter queue bit further up, we enjoyed what we did, but not too much time to shop in between, much to my hubbys delight.