We'll be traveling from Paris to St. Goar. The plan is to stay overnight in St. Goar, cruise to Bacharach and take a train to Venice. Is this doable?
Where would we get the train to Venice? Through Bacharach?
Go to the Deutsche bahn website. Enter Bacharach in the "from" block, then enter VENICE in the "to" block, date and time you want to go and, Voila! All you options. Minimum 3 changes and 12 to 14 hours. http://reiseauskunft.bahn.de/bin/query2.exe/en?ld=96252&seqnr=5&ident=nx.024753252.1365123446&rt=1&rememberSortType=minDeparture&REQ0HafasScrollDir=2
Don't do that. It is too long of a journey from Frankfurt to Venezia. Day trains take more than 8 hours, night trains are crap and much slower and require yet changes. Take a flight from Frankfurt to Venezia (or worst case Milano Malpensa airport + train).