Family trip Train to Rudesheim/ Boat back to Frankfurt

We are independent travelers and would like to take the train to Rudesheim and boat back to Frankfurt.

Cruising from Rüdesheim to the NORTH will provide the Rhine Gorge scenery you are after. South of R'heim there isn't much to look at, so the cruising options are skimpy. So instead of cruising back, you should plan to use the train to return to Frankfurt. Here's a map of the best cruise segment:

https://i.pinimg.com/736x/ca/e1/50/cae1500f42cf03c44bea2da512d659a0.jpg

Most of the cruise boats terminate in St. Goarshausen or St. Goar. St. Goar is the more interesting town, so I'd stay on the boat all the way to St. Goar and get off there. You can tour Rheinfels Castle there if you like.

Two additional villages to visit: Oberwesel and Bacharach.

The best way to see them is on your return trip by train from St. Goar to Frankfurt. (This is better than trying to get off the boat on your way to St. Goar because trains run very frequently between these towns.) It's only 5 train minutes from St. Goar to Oberwesel and then 5 more to Bacharach. See map of the train lines which connect these towns:

https://i.pinimg.com/originals/7e/28/f2/7e28f27b065b0991f133fb11e5f56c79.jpg

You should have no trouble finding wine in any of these towns.

Once you've seen Oberwesel and/or Bacharach, you will catch a train or combination of trains back to Frankfurt.

The Day Ticket for Germany is a day pass that permits unlimited trips by regional train and can be bought for 5 adults (€82) to cover all your train rides. (Note that on weekdays there's an after-9-am restriction.) To find train schedules, use the DB link below:
https://int.bahn.de/en

Show the train ticket at the KD cruise kiosk to get a 20% cruise discount.

KD cruise boat departures from R'heim to St Goar are at 9, 11, 14:15 and 16:15.
https://www.k-d.com/fileadmin/KD_Fahrplaene/KD_Fahrplan_2024_web.pdf

Taking the ship back to Frankfurt would take hours. This is not a regular ship route. You want to go to Rüdesheim from Frankfurt on the train and take the ship to Sankt Goar or St. Goarshausen. Wine tasting can be done just about in any town in this area. Show your train tickets for a discount on the ship.
A fun place to stop for wine tasting is in Rüdesheim at RheinWeinWelt. The train station is located right outside the venue, so easy to get home after having a few glasses.

It's important to your valuable vacation time that the train is massively faster than the boat, especially upstream towards Frankfurt. In a general sense, the dayboats in the scenic Middle Rhine don't have enough daily trips to be regarded as a hop-on municipal bus service. If you plan carefully and restrict your shore time, you may be able to boat to two towns. Download the KD schedule covering your travel dates.

Thank you so much for your helpful replies—so great to get detailed information! If you should ever need information about San Francisco and the Bay Area in California, I’m your person!

Just to clarify, Frankfurt is not on the Rhine, for one thing. So it's not a normal part of a cruise experience. It would be good to read a guidebook on the area, which might cause you to have more questions. It would also have general info on how to buy train tickets, and which towns are worth a stop.

I personally found that the KD boats were not numerous enough to treat them as "hop on, hop off" busses. You need a targeted approach to your dayboat experience; Whatever you're interested in, castles, old towns, cable cars, art. It's not at all like visiting a winery, but I would note that there is a wine cafe right across the street from the (unattended) Boppard train station. It's easy to wait for the next train there, but I'd get the bill paid in advance so you can be sure to make your train. (Having already bought your ticket at the machine in the station, if you don't have an all-day ticket or whatever.)

In general, my experience was that serious or famous wineries in Germany absolutely require a reservation or a prepaid tasting ticket. Of course, I'm not talking about town square wine festivals, which tend towards September, not your trip. But check local calendars.

As noted, the only important scenery is between Bingen and Boppard or St. Goar. And that is downstream, so slightly faster on the boat (but it's not so that you miss the views!) Usually at least sausages, beer, and wine on the KD boats. Remember sun protection.

Concur with Russ above and many others have recommended the same. We'll be staying in Rudesheim and plan to take the KD Cruise north from there to St. Goar then various trains back visiting Bacharach and/or Oberwesel. Going north is actually going downstream and much faster than taking a boat the other way.