K-D cruise line from Rudeshein am Rhein to Boppard

You might have to. This year, the only through boat from Ruedesheim to Boppard is the 16:15 departure from Ruedesheim. If you take the 11:00 departure, you will have to change at St Goar after you arrive at 12:40. Then you have your choice of traveling on to Boppard at 14:30, 15:30, 17:30, or 17:55.

Check out the schedule at https://www.k-d.com/en/

You can hop off and back on later. When you get off in Bacharach or Oberwesel, for example, you will need to have your ticket marked by the crew as you leave in order to reboard later.

You will also need to have a plan for the day... you must know WHEN the next boat is passing by, and if the boat you hop on terminates in St. Goar or St. Goarshausen, you'll also need to know WHEN the next boat heading to Boppard will leave after that. That might sound simple, but there are only a few boats per day. Pay close attention to the schedule and watch the time carefully.

Will you be taking your bags with you onboard? That's permitted, but the small towns you'll be visiting will not have lockers at the train stations or elsewhere. Sometimes the TI offices will hold bags for you if/when they are open - St. Goar's does this - but you will need to look into their hours of operation carefully in advance if you plan to use this service.

All in all, it tends to be a lot simpler if you just take the whole cruise at one time (if possible.)

Will Boppard be your final destination? If so it's an easy matter to leave the bags at your hotel and to backtrack BY TRAIN from Boppard to St. Goar, Oberwesel, Bacharach, etc. It takes almost no time at all to do this since the towns are so close to each other. St. Goar is 10 minutes away, Oberwesel 15, and Bacharach 20 minutes. And train service is hourly or better all day long. Boppard makes this train hopping off and on even easier with the VRM Guest Ticket, a freebie rail ticket good throughout your stay. It's valid as far south as Oberwesel on this line (buy an add-on ticket for the Oberwesel > Bacharach segment at €2.70 per travel leg.)

Thank you all. Very helpful.