If you buy a day ticket,can you get off and back on at different stops on Rhine? How long are the stops and how long does it take to get from Cologne to Bacharach and then to Heilelberg. I thought this might be an alternative to train travel for a short period.
I don't think it would be a good alternative. The one hour boat ride from Bacharach to St. Goar is 14km and takes probably 10 minutes by train or car.
The difference may be even more pronounced when the road doesn't follow the curves of the river and the speed limits are higher.
The boat will also cost considerably more than a train, especially the local train which can be hopped off and on (just check the schedule for the next couple of departures so you know whether you need to hurry or take your time getting back to the station). The trains and boats both run regularly although (at least in fall) they can often run an hour apart.
It also depends on how you like to travel.
Some people are trying to get from Point A to Point B. All they care about is how to get there the fastest and cheapest way.
Then there are others who want to also enjoy the journey between Points A and B. Personally, after days of harried travel, an hour cruising down the Rhine isn't a bad thing. Get yourself a beer, put your feet up, and enjoy the beauty of the river.
It's been years since I did it so I can't say much about schedules and such. But I remember the trip and truly enjoyed it.
Surprise, surprise!
There is no K-D boat connection all the way from Köln to Bacharach. The best you can do is to take the 8 AM boat out of Bonn, which is 3 hours by boat from Köln or 24 min to the Hbf by train. That boat gets to Koblenz at 1:10 PM, and another boat leaves Koblenz at 2 PM, getting to Bacharach at 6:30 PM. That's 10-1/2 hours in transit! If you don't count 50 minutes in Koblenz, the actual time on the boat is over 9-1/2 hours.
The only boat that leave from Köln does so at 9:30 in the morning, but it only goes to Bad Hönnigen (3:25 PM). You'd have to spend the night there and catch the 8:05 boat the next morning. It gets to Bacharach at 3:30 PM.
The K-D site does not even mention any boats to Heidelberg.
Note, K-D does partner with Pemicon, which runs cruises from Düsseldorf to Basel, Switzerland, but these are very expensive multi-night cruises in cabins, and probably don't let you off at other than scheduled stops.
Thanks to everyone for your great input on river cruises - you've convinced me to stick with trains since they're much faster.
Once you're on the Rhine after Koblenz you'll find many choices for cruising. It's noted that the best of the Rhine is around St.Goar-Bacharach-Bingen for just cruising.
For example, we bought RT tickets for St.Goar-Bingen on a boat that stopped in each place. This allowed us time to enjoy some cruising and to hop on/off to go wherever. In Bingen we saw some of the flower show. Then we ferried across to Rudesheim for wine tasting shops and lunch. Then we hiked the trail from the Niederwald monument and hopped back on a boat in Assmanhausen.
Some people just stay on and cruise and relax for 2-3 hours and they do offer RT cruises without stops for this reason.
So it depends on what you want to do.