Some info for future foot passengers:
The ferry arrives at 0645 in Caen and by 0700 you can be walking out the front door of the terminal (I stopped for a quick cafe).
Walk straight up through the carpark in front of the terminal and onto the main road, about 50yds on the right (heading away from the ferry) is the No 61 bus stop which will arrive about 10-15 minutes later.
Bus fare 1.50eu to the Gare SNCF (30 mins).
There is then a 0904 to Le Mans (direct) @ 27eu (they run every 90 minutes) so there is time to have another cafe et pain au chocolate, play the piano in the station and in 90 minutes (the 4th stop) you will be arriving in Le Mans.
From there it's the T1 tram from right in front of the station (direction Antares MMArena) to the end of the line and just a 15 minute walk Les Epinettes.
I can recommend the bus/train/tram route as very achievable and the timings would seem to work in return as well as a train leaves Le Mans at 1755 arriving Caen 1940 which would get you to the 2300 ferry (there is a 1958 arriving 2149 which is doable but could be tight unless you get a taxi).
I had actually bagged a lift - 2 to be honest:
Mrs W and the crew had met up with a stag do on the Tue ferry who had a spare space in their minibus - but that was a Thu AM sailing (not PM) so not a lot of use.
I also met a decent old cove in the foot passenger queue on Thu night who was on his way to his 35th Le Mans and was being picked up in France and offered a lift. However as we tried to board the ferry, his ticket was rejected - he was a Le Havre passenger not Caen - you see we hadn't actually talked about which port he was being picked up at or I was going to. Ah well...the train worked very well