That's about half an hour at a not that fast 25 knots.
30 minutes from a city center. For any coastal city, that is likely to be no worse as the time to get to an intercontinental airport.
Still means about 2h00 from NYC to Shangai, door to door. Quite an improvement over the 17hours today.
Non coastal cities have a problem...
In any case it takes care of most nimby as it's to far away for the neighbors to care. So reasonable, in that aspect.
Of course ITAR, fear of nuclear strikes etc... general FAA/EASA regulations remain issues for this business plan.
Weather will also be an issue. Flights rarely get canceled for weather issues. But transferring from a ferry onto a barge at high sea in bad wind seems like an non fun experience in a three piece suit.
