I must admit to being a bit confused by the posts. St Marks Square is quite a distance from the cruise port, especially if you have luggage. Yes, you can always take a water taxi but that is going to cost you over $100. If you do not have much luggage you could simply take the vaporetto (6.5 Euros for a single ride or other deals for 24, 36, 48, or 72 hour passes) assuming you can handle your luggage (they do charge extra if you have more then one piece). The nearest vaporetto (also known as the ACTV) stop to the port is at the Piazale Roma which is a 15 - 20 min walk to the port with a slope when you go over the bridge. Some of the cruise lines run a free shuttle from the Piazale Roma to the port and it is also possible to get a land taxi at the P. Roma to take you to the port for about 15 Euros. Your best bet would be to take the Aliliguna "M" line which is a private boat company. This M line runs from St Marks Square direct to the cruise port. This line also charges 6.5 Euros (one way) with a 3 Euro fee for more then one piece of luggage. The M line runs every 30 min from St Marks Square leaving at 5 and 35 min past each hour.