This may be too late to help Janfred but nearly all ships dock at the cruise ship complex located near the Piazale Roma. It is possible to get the Alilaguna Line boat from the port over to St Marks Square although this is normally not the best way to get around Venice. There is a new People Mover which is a small automatic train that runs from the parking area out in Troncheto over to the Port and finally over to the Piazale Roma. This People Mover costs about 1 Euro and only takes a couple of minutes. Once at the Piazale Roma it is easy to walk across the square to the ACTV (vaporetto piers) where you can get the vaporettos to anywhere in Venice or the other islands in the Lagoon (i.e. Lido, Murano, Burano and Torcello). A single ticket on the vaporettto (or the Alilaguna) costs 6.5 Euros. However it usually makes more sense to buy a timed Vaporetto ticket that allows unlimited use over a period of time (12, 24, 36, 48, 72 hours). As a rule..if you use the vaporetto as few as 3 times in the first day the timed tickets are a bargain.