We have friends who are wanting to do a Danube river cruise. Husband is a solo cyclist, wife does not cycle at all. So plan is he cycles along the route during the days, while she stays on the boat and does the boat organised day trip by coach etc. We would like to join them but of course tandeming being  twice the fun that is the way we would want to do it. We have been told we could bring our own tandem, but boat will only accept them if they come in two (notwithstanding that our Circe Helios is only marginally bigger than a large solo). Does anyone have experience of river cruise ships that will allow you to bring your own tandem? There must be some as Santana seem to be able to charter them, but maybe that explains why Santana's wonderful sounding trips cost so much money.