That is a nice idea, Tom, but the Danube is no river to mess with. It's big, has some sorta fast sections, is loaded with rather large barges and other boats of size... and it's got some interesting pollution problems.

I'd like to see these guys in a large tripping canoe of about 18.5' with outrigger floats one foot from the widest point on the hull, standing clear of the water unless called into use. No drag penalty and enormous secondary stability for peace of mind.