Getting to Cassis from Marseilles??

[mimicsr]

Has anyone taken the boats from the port in Marseilles that go to Cassis by way of the Calanques?? We are on the 10/22 Splendour and dock at 7:00 a.m. and leave at 7:00 p.m. I've read the boats leave at 2:00, and it's a four-hour trip, so they would get back at 6:00, not leaving much time to get back to the ship. Can you go by train or bus to Cassis, then catch local boats just to the Calanques for shorter time periods, then back to Marseilles by bus or train again? We know we could hire a driver or take a taxi, but our grown children are with us this time and they're on a rather tight budget. Since DH and I have cruised Europe twice before, we sort of know the in's and out's of doing it on our own. Thanks in advance for any suggestions.