From 10 July until 12 Dec. the tracks will be under construction on the right side of the Rhein, all the way between Wiesbaden and Neuwied. This will include the towns of Eltville, Rüdesheim, Assmanshausen, St. Goarshausen, Braubach, Lorch, etc. that are on the RB 10 Route.
Look for the replacement (Erzatz) buses instead and count on the ride lasting a lot longer than the train would take.
A lot of bike riders are due for a shock.
This rail-line map includes the impacted railway:
https://www.seat61.com/images/rhine-train-map-detail.jpg
Here's the good news if you wish to visit the right-bank towns WITHOUT the possibly arduous bus ride...
The west-bank railway (Mainz > Bingen > Bacharach > St Goar > Boppard) stops in towns with ferry service that is frequent and will get you across the river:
Bingen < > Rüdesheim
St Goar < > St Goarshausen
The east-bank town of Braubach, home of Marksburg Castle and probably the most popular destination between Rüdesheim and Koblenz, does not have ferry service. But it is only a short distance south of Koblenz. So if you have a booking on the west bank in St Goar or Boppard, for example, you can... 1) take a west-bank train to Koblenz Hbf, then 2) catch either the direct SEV (Ersatz) bus or the regularly-scheduled and also direct local bus #1 to Braubach. This Koblenz > Braubach leg will take only a little longer than the train - about 20-35 minutes. Both bus options travel Koblenz > Braubach every hour which means two bus options every hour. (Note also that Bus #1 actually begins its run from Koblenz down by the Deutsches Eck and the cable car ride; if you are visiting this part of Koblenz, you can board bus #1 right there and ride all the way to Braubach on this bus with no changes.)
Also, the cruise boats which operate into the fall months stop in these towns as well - K-D and Bingen-Rüdesheimer have a variety of cruise options with stops on the east bank.
In 2004, I was staying in Boppard and wanted to see the Marksburg. The K-D boats were not running yet, so I took the ferry across at Boppard, walked the Approx. km to the station in Filsen, then took the train to Braubach. It was easy.
Actually, except for that train ride from Filsen to Braubach, I've never really spent much time on the right bank. All the rest of the places I wanted to see, Boppard, St. Goar, and Bacharach, are on the left bank, as is Bingen Stadt, from which I started my Rhein cruise back to St. Goar.
In 2004, I was staying in Boppard and wanted to see the Marksburg. The
K-D boats were not running yet, so I took the ferry across at Boppard,
walked the Approx. km to the station in Filsen, then took the train to
Braubach. It was easy.
Normally, the Bopppard ferry is a good way to get to Braubach from Boppard or another nearby town on the left bank. The ferry crossing time is just a few minutes, the walk into Filsen a few more - and you time those first two steps so that you can do as Lee suggests - catch a train from Filsen to Braubach (which only takes 7-8 minutes) without a long wait at Filsen station for the next train.
In the coming months, however, this approach will not be possible for two big reasons.
1) Starting next month, the trains between Filsen and Boppard will be idle.
2) The Boppard ferry crossing is out of commission right now and for the foreseeable future. It has been down since March, when some oversized vessel rammed and destroyed the ferry dock on the Boppard side. Local authorities still have no idea when the dock and the ferry will be back in service. For now, the most practical approach is the one I suggested, the Boppard > Koblenz > Braubach strategy by train + bus.
The K-D ship can sometimes be a good way to get to Braubach - thanks to Lee for mentioning it. It uses a different dock in Boppard and is currently in operation. But using it comes with conditions...
There is only ONE K-D SHIP per day at 10:15 which makes this crossing (30 minutes from dock to dock) in time for a tour of Marksburg.
This ship does not operate on Mondays.
The English-language tours of Marksburg are scheduled for 13:00 and 16:00, so once you are at the Braubach dock, you will have some significant time in Braubach prior to your English tour; lunch and a walk around Braubach (a beautiful town!) are good options, or just go straight to the castle for a German-language tour and follow along with a pamphlet in English.
There are only two ships per day returning to Boppard (13:05 and 18:55) and no ships at all on Mondays.
The one-way Boppard > Braubach fare costs 17 Euros p.p.; round-trip is 20 Euros. Boppard > Koblenz > Braubach by train + bus is entirely free of charge for those who stay in Boppard (VRM Guest Ticket.) Also...because this 30-minute cruise doesn't cover the most scenic part of the Rhine (Bingen > St Goar,) I think the K-D ship would be an unusual choice for most people.
Current report on the Boppard ferry situation:
https://www.boppard.de/aktuelles/faehrbetrieb-in-boppard-ruht-nach-unfall-wie-geht-es-weiter/#accordion-1-5
