look up a couple pics of a vaporetto. there are in 2 sizes. the typical big one on the grand canal is just a big flat floating dock. you enter in the center and stand(unless you are lucky). it makes about 15 stops. you can get on and off at whatever stop you wish. tickets are sold for a single trip, or for a time frame. i think transit grand canal takes about an hour from the train station to the end of the island. when they cross to lido, they move about 30mph(50kph).

the ride up the grand canal is a real delight. i get a seat and rest, while riding that piece of the canal. i usually do it twice a day, now that i have gotten very old.