It’s really the ideal application for a hovercraft.
Which is why BARB have two, with a new fast replacement for their small craft being sought.
Would I sail a boat across from Bristol to Cardiff? Hmmm, I’ve spent many hours over many years around or crossing the Severn, and I’d want to be very, very experienced, particularly with regards to navigation before even thinking about it. Quite apart from the speed of the current and the tides, there are lots of shoals and narrow channels that are visible from the bridges at low tide, but very difficult to navigate around once the tide starts to rise.
[edit] The steam ship is the Waverley, a paddle steamer, which runs trips. I’ve been on her for an evening works trip, and it was great fun. I’ve seen the Matthew making her way upstream too. [/edit]