We are in Tuscany now, but would like to go to Sardegna for a week or more. Can you advise on the ferries going from Livorno, Civitavecchia or Piombino? We have a rented car we'd like to take to the island. I'd also prefer a day time ferry, rather than an overnighter. Thanks!!
The fastest is from Civitavecchia (6.5 hours). From Livorno it's at least 3 hours more). It's also cheaper to cross from CV, generally.
You can check the following companies for the various options. There are deals offered so you need to check all.
Tirrenia
Moby
Grimaldi Lines
Corsica-Ferries
There are also websites that do searches of the best price (directferries.it)
Two persons with a vehicle is going to cost you about €200-250 round trip.
Check also with the rental company about contract restrictions on putting the rental car on a ferry. Some don't allow it.
Roberto has you on the right track. Buon viaggio!