Hydrofoils are great when they work. Using them in places where there are lots of debris in the water (say a city harbor) does not seem like a good idea. When I was a kid they tried running hydrofoils between Seattle and Victoria BC. When they worked it was great. Pretty fast and a nice ride. But the boats kept hitting deadheads and damaging the foils. Then the boats had to cruise to port just like any other boat, slow(er) and in the waves. Not much of a difference then, plus they had to repair the boat.
IMO, it won't take many instances of the Seabubbles dumping the passengers in the water (it is an open boat) because they hit an old tire at speed in the river/harbor/whatever before people decide that there is a better way to get there.