Luggage during cruise on the Rhine

It appears that the tourist office will store luggage for free during the hours it is open. I cannot vouch for this information, but it appears on the TO's own website, so it sounds pretty reliable. Note that the office's hours vary with the time of year.

"We are picking up the ship in Boppard, making a stop in St. Goar then onto Bacharah."

I take it you are sleeping in Bacharach, right? So wouldn't it be better if you didn't have to schlepp bags to the boat in Boppard, off the boat in St. Goar and to the TI office, and back on the boat again, and to fuss with them during your cruise? It would also be better to see the entirety of the most scenic section... So don't pick up the ship in Boppard. Wherever your day starts, I suggest you take the train straight to Bacharach and drop your bags at the hotel - that means just ONE shuffle with your bags.

THEN... while it is possible to board a boat in Bacharach, it's much wiser to take the train to Bingen (10-12 min.) to start your cruise north to Boppard. The part south of Bacharach, which your first plan overlooks, is part of that scenic section - BETTER IMO than the part between Boppard and St. Goar. If you skip this part you miss several handsome castles, like Rheinstein:
https://www.uli-franke.de/wp-content/uploads/2014/07/20140622_144833-Burg-Rheinstein.jpg

The last part of this cruise (St. Goar-Boppard) could be skipped if you're short on time by ending the cruise in St. Goar. Boppard is only 10+ minutes from St. Goar by train in case you really want to get there.

From Bingen it's 2.3 hours north by boat to Boppard - cruising with the current (from south to north) you see more territory in less time. You can stop over in St. Goar either by boat or after your time in Boppard (when you return to Bacharach by train.)

Here's a map of that most desirable Rhine segment between Bingen and St. Goar: http://www.bingen-ruedesheimer.com/images/map/rhine-valley290.jpg

I want to emphasize what Russ said about the direction of travel. You want to go DOWN the Rhein (down as with the flow, not down as on a map hung on the wall). The current on this part of the Rhein is very strong from the southeast and the boat does not go very fast against it. I made the mistake of going against the current in the*** direction*** of Koblenz to Mainz and sights passed so slowly. You can only look at a town or a castle for so long before you want to see something else.

Regional Bahn trains (MRB and VIA) run hourly in each direction on both sides of the river, stopping at every station. Plus there are faster trains that only stop at a few stations.

If you are going to spend the night on that part of the Rhein, check in first, then take the train to where you want to start your cruise. By the way, if, at the kiosk where you buy the boat ticket, you show them a Bahn ticket that got you there, you get a 20% discount on the boat ticket.

Thank you! I did not realize the down river and south were not the same thing. I greatly appreciate the suggestions and am looking foward to our trip!!!