We took the ferry from Naples a couple of years ago in October. Very cheap and easy to get to as the ferries are close to the cruise terminal. Only problem was that on arrival in Capri there were massive queues for the funicular (to reach the town)although these did not take too long to disperse. I imagine that there will be even more people around in August! Jill.
It would be very helpful to know which ports of call you are talking about. Capri from Naples or Sorrento in eminently possible provided you use the ferries and some are faster than others. As for the other ports I don't know. ... Neil.
We took a ferry from Naples to Capri and it was really easy. The ship docked very close to the ferry port and a short walk got us there. Be aware however that we were accosted by a young enthusiatic girl(one of many) who asked did we need to know which ferry we needed and took us to the ticket office, then held out her hand for a tip which we gave her for her cheek! The ferries run frequently and although the crossing there was fine on the return journey the weather had turned and we had one of the most frightening crossings you can imagine. I am a good sailor but loads of people were vomiting it was so choppy. Capri is lovely and worth the trip so good luck. Carol.