Hello, we will be in Germany near the end of October 2017. We will arrive to the Rhine/Mosel River areas on Saturday Oct 28th (coming from Berlin via train) and want to see the river(s) and castle(s) on that day primarily. We want to be at the Nurburgring on Sunday Oct 29th and then continue into Belgium. It seems that we will need to rent a car to prevent it being a nightmare getting to the racetrack. I'm also having a hard time finding boat options from the south (Bingen? Bacharach?) to the north (St Goar? Koblenz?) this late in the year. Are we going to miss out on a Rhine and/or Mosel boat ride in late October?
There should still be ships running at the end of Oct. Start your cruise in Bingen, Rüdesheim or Assmanshausen. If you only begin in Bacharach, you miss 3/4ths of the castles. That is too short of a cruise to even bother with.
Are you looking on the KD website?
Regularly-scheduled KD cruises are possible through 10/22:
Bingen-Rüdesheimer operates cruises through 11/5 (in German):
(See "Loreley-Fahrten" cruise schedule on the upper right of this flyer to cover the most scenic part of the river - Bingen to St. Goar; the KD schedule offers the same cruise segment.)
It's just under 1.5 hours of cruising, whichever company you choose. Then use the trains to return to your car in Bingen (stopping on the way to sightsee in St. Goar, Oberwesel and/or Bacharach on the way back.) Here's a map of the target cruise zone:
Rüdesheim can be a starting point as well (though you don't get much more scenery since you merely cross the river over to Bingen.) Aßmannshausen would mean skipping some of the nice scenery immediately north of Bingen - I'd do R'heim or Bingen instead.
If you cruise only Bacharach to St. Goar you miss out on the excellent part just south of Bacharach.
Cruising beyond St. Goar can be a bit repetitive of the previous sightseeing and becomes a waste of time and money the further north you cruise (especialln near Koblenz, where some of the scenery gets a little industrial.)
I'd suggest a tour of Marksburg Castle - a never-destroyed medieval knights castle in Braubach: