Scrovegni Chapel on our own from cruise ship

I think Uniworld is a river-cruise company, so maybe they are not affected by Venice's restrictions on ocean-cruise ship anchoring. Just be sure about where you'll be starting from.

I'm sure there are lots of weekday trains, but it's probably a half-hour walk (if you don't hit the Vaporetto schedule well, and have a way to pay the fare) from the Venice train station to the cruise terminal you named. So half-hour to wait for the train, half-hour on the train, half-hour walking back to the last boarding time for the ship. Worst case, bigger bucks for a taxi. But the taxi can't go to the cruise terminal, of course.

I know you don't want to "pay" for the ship's excursion, but you could arrange with the guide to leave the official group and rejoin it at the bus pickup point, which would give you the assurance of meeting the ship, and not having to do any independent travel planning (other than booking the popular Chapel in advance.) I would confirm with the Cruise Director that you can do this. Is the trip "included" in the cruise?

Yes, Uniworld is a river cruise. And the walking tour of Padua is included in the trip. Uniworld busses us from the San Basilio wharf to Padua.
The walking tour does have free time for lunch.
So it's good to know that the Scrovegni doesn't take a lot of time.
I appreciate all the suggestions!

JBC, it isn't so much that the Scrovegni doesn't take much time; it's that your visit is limited to only 15 minutes! But it is certainly well worth the trip.

Check out the website for details; you must buy your ticket in advance, and you will have a very strict timed entry. www.cappelladegliscrovegni.it.

Padova is a lovely town. Nice university, piazzas and restaurants. I am sure there will be a lovely and informative walk through town to the Basilica of St. Anthony and back. Italy has lots of lovely towns and Basilica's. BUT, the Scovegni Chapel is spectacular. Because of the timed entrance for it - and because each group has to sit and wait in a climate controlled room to limit the outside humidity entering with them - I am not surprised that it is not "on the tour." Use your cruise excursion for transport. Book as early a time as you can manage logistically at the Chapel, or near lunchtime, and time your arrival at the Chapel well in advance and leave lots of time to sit being acclimatized before your actual tour. Set several possible sites with your guide to rejoin the group as they have wandered on. I expect the Scrogveni Chapel will be your principal and maybe only memory of Padova in five years.

Seems wacky to me for a tour to go from Venice to Padua and not include the Scrovegni chapel!

I hope you can confirm with someone at Uniworld that you can peel off from the walking tour to spend about 45 minutes to see the chapel (you spend as much time in a special climate-controlled room as you do inside the chapel). If not, Google Maps says that you can do the whole trip in one hour and 2 minutes, including walking 22 minutes to the train station in Venice and 13 minutes walking from the train station in Padua to the chapel, but of course that is not taking into account the time it takes to buy a train ticket, get oriented, maybe get a bit lost. But still, even doubling the Google Maps time estimate, a do-it-yourself trip to see the chapel on your own seems doable and well worth the trouble.

Maybe someone on this forum has actually done this trip --- we have only taken the train from Padua to Venice, but we found it very quick and easy to do.

In the room in which you are getting de-humidified and whatever else is happening, you are sitting in chairs and watching a nice little video about the paintings.

Thanks to all for you help. Very much appreciated.

Entry groups for the Chapel are very small. I bet the capacity of Uniworld's bus would fill multiple entry groups, so including the Chapel on its tour would not be workable.

There's a tram in Padua that runs from right near the train station, past the complex where the Scrovegni Chapel is located and on past or at least near St. Anthony's. It's very useful for sightseeing in Padua; you just need to be sure you get the tram going in the right direction. I'm not positive there's an easy-to-use ticket machine at every step, though. I've always arrived in town by train and stopped at the tourist office right outside the train station to buy the city's combination transit/sightseeing pass. If you use the Uniworld tour to get to Padua, that probably won't work for you.