Rhine boat ride

this is the company I know: K-D rhine Their website should answer your questions. Just note that going North is going downriver, faster than going upriver.

https://community.ricksteves.com/travel-forum/germany/rhine-river-day-cruise

https://www.kdrhine.com

And there are other companies.

I suggest you AVOID the KDRhine site. That is a middle-man site which sells day passes.

Here is the official site:
https://www.k-d.com/en/

You do NOT need to pre-purchase anything. In fact you will get a 20% discount if you buy tickets at the dock (and show the train ticket you used to reach your cruise-start town.)

The best cruise-start town is NOT Bacharach... Catch the train from Bacharach to BINGEN to begin your cruise. In Bingen, buy a ticket to St. Goar or Boppard - that will give you a cruise through the most scenic part in 1.5 or 2.3 hours, respectively. Your course to St. Goar should cost about €16 this way - or a bit more to Boppard.

Here is a map of that popular and most scenic river segment between Bingen and St. Goar:
https://www.bingen-ruedesheimer.de/pub/media/wysiwyg/Rheinlauf/Loreleyfahrt_zugeschnitten.jpg

Then you can sightsee in those towns and return later by train to Bacharach. ST. Goar is home to Rheinfels Castle (take a tour.) Boppard is a handsome town with an exquisite chairlift ride to a scenic lookout.

There is no need to cruise all the way to Koblenz as the scenery deteriorates somewhat as you approach Koblenz.

If you choose to begin your cruise in Bacharach and head north, you will miss half of the most scenic part (which lies to the south.)

Russ, thanks for the catch! There's another thread on here about the danger of trusting search engines.

Thanks everyone, so helpful. We were just thinking of going to Koblenz to see where the Rhine and Mosel connect. Maybe it's not worth our time. Sure appreciate everyone's input.

We were just thinking of going to Koblenz to see where the Rhine and
Mosel connect. Maybe it's not worth our time.

Not knowing your plans, I suggested Rheinfels Castle once your cruise ends in St. Goar. But if you intend to head north after the cruise, it's not a problem - just use the trains. The most interesting castle tour on the Rhine IMHO is actually at MARKSBURG Castle, not a set of ruins, but a genuine, intact medieval castle - and it's in Braubach, about 10 minutes south of Koblenz on the east bank. So you could probably do a cruise from Bingen, take the train to Braubach for the castle, then the train to Koblenz on this day. That's pretty simple. If you like that idea, follow these steps...

• Catch cruise from Bingen as outlined earlier (11:30 from Bingen?)
• Get off in St. Goarshausen on the east bank of the Rhine (arrive 13:05) instead of St. Goar.
  
• Take the 13:32 train north to Braubach (arr. 13:53) and have lunch, then walk up to the castle for the 4 pm English tour.
• Return to train station for the 17:54 train to Koblenz (arr. 18:06) and walk to the Deutches Eck (Rhine/Mosel confluence.)
  
• Find dinner and then take a train back to Bacharach whenever you are done with Koblenz.

All your train travel is covered by one day pass - the Rheinland-Pfalz ticket:
https://www.vrminfo.de/en/tickets/tickets/ticket-offers/rheinland-pfalz-ticket/

(This ticket will get you the 20% discount at the boat dock in Bingen.)

I realize you have a rail pass - but this day pass price is pretty good, and perhaps you could use that rail pass day you bought somewhere else, if needed.

Wow, thanks so much Russ, this is perfect!

At the Rhine/Mosel confluence, take the cable car across the Rhine to the Fortress.