luggage on vaparetto

I've read one bag per person isn't an issue, but after that, it gets iffy.

I, too, would like some clarification on this.

What sizes are the bags? Do you mean just one suitcase per person, which you can easily handle yourselves, plus a small shoulder-bag/handbag? I've had no problem with that amount of luggage on a vaporetto, but there are fees for more than one large piece. The vaporetto usually gets crowded somewhere along the journey, even if not at your boarding point, then at least by your destination point. See also this thread from last year: https://community.ricksteves.com/travel-forum/italy/riding-the-vaporetto-in-venice-with-luggage.

The largest suitcases we bring to Europe qualify as airline carry-on size, even if we choose to check them on the flight: http://www.ricksteves.com/travel-tips/packing-light/packing-smart.

My family had no problem bringing a check in size roller bag (each) on to the vaparetto and we rode it all the way to the stop before St Marks.

We have taken larger cases with no issues. Just try not to block the gangway area.

Suitcases shouldn't be a problem, but I'd suggest keeping them close to you so they don't impede other passengers. If any of your group will be wearing Backpacks / Daypacks, take them off when you board the Vaporetto and place on the deck (if you forget, the driver will probably mention it uisng words like "Il Zaino sul terra").

Our family of four each had a small roller bag and a small backpack.... we got on without much issue. It was a bit challenging, but over all no trouble. The vaporetto stops on opposite sides of the canal - you might check in advance to see what side your stop is on so you can try to be nearer that door, and not have to cross all the way across with your luggage if it's super crowded.

Kim

For five people, enjoy a taxi ride.

For 5 people, the vaporetto will cost a total of 35 euro. A water taxi will cost about twice that.
If your hotel is in the center of one of the islands, far from a vaporetto stop, the splurge for the taxi might be worth it. The taxi can get you very close to your hotel or even right to the front door if it has a canal dock.
If it is close to a stop vaporetto stop, and especially if you will be buying a vaporetto pass for every one, then go with the vaporetto. I've had no problem with a 22" roller board and a back pack hand carried on.

My mom last year had a checked size bag (maybe a 26 inch) as well as a 20-21" carry on, and she had no issues...they just directed her to put her bag on or under the rack on the vap. Hubby and I with our carry on size just stood over to the side with our bags trying to stay as out of the way as possible...

The area just behind the captain's wheelhouse is the designated area for luggage. Keeping it with you would create traffic jams, particularly if you are a knot of several people. Stack it up and leave one person to keep an eye on it. If you standing just behind it you can look out the open area to both sides with a relatively unobstructed view unless you are very tall (have to bend down for a good look) or very short because the hordes of taller people may partially obstruct your view. The open decked area there has the second best viewing area on the boat - after the front facing seats forward of the wheelhouse (don't stand there, only sitting is allowed or the captain will shout at you) and better, just, than the seats at the stern.

As Ken says, backpacks and rucksacks must be removed.

From our experience last week, it seems like you can take bags with no trouble. We had 2 small Paul behinds and a shoulder bag each. We actually watched a girl lug 4 huge bags along with numerous carried bags onto the vaporetto to Murano.