Navitalia recommends

Be present at check-in at the ports of departure at least two hours in advance of the embarkation time set by the chosen shipping company. Arriving later than the check in time or the departure time will result in the loss of your ticket.

Remember to bring your ticket or voucher and a valid identification document for your chosen travel destination with you when you check in (Navitalia.com recommends visiting the Polizia di Stato website for more details at the following link: http://www.poliziadistato.it/articolo/24725/

Last and most important recommendation:

"ENJOY YOUR BOAT TRIP MINUTE BY MINUTE:

THE HOLIDAY BEGINS!"