How about Puget Sound (Seattle, Tacoma, Olympia...), where there are ferries all over. Several routes have "foot ferries" (no cars) offering rides with added speed to get the commuters to home or work across several miles of semi-open waters. Only rarely are waves a serious factor, and I don't know if that's even serious enough to affect this watercraft.
Just one example of where this could really be useful and profitable. I can think of others.. Chesapeake Bay, Lake Champlain, Great Lakes...
What about between OAK and SFO terminals inside security, so that connecting flights (or East Bay passengers boarding and returning) could transfer to & from international gates at SFO?
The Great Lakes are not that choppy on average except during storms. But the primary use case would be along intercoastal waterways and rivers, which are also very calm except during storms.
There are plenty of places where the water route is much, much, much faster than the land route, and there are plenty of islands that are only accessible by boat.
Wikipedia says the lake is 483 km², while Lake Champlain is about 3x bigger at 1,331 km².
From Google Street View it seems the mainland is visible for nearly every direction.
Oh! I found another ferry, a car ferry from "Boheden, 956 93" to "Sandudden, 956 93 Överkalix", according to Google Maps. The lake Djupträsket is 8.68km² and the ferry is a few hundred meters.
And one between Sund and Jarenleden, on the lake Stora Le, 131 km² but it's narrow and the ferry is only about 600m.
Sweden has a LOT of lakes, and most of them are narrow. I assume they were made by glaciers? I found those two ferries by looking for two roads ending on opposite sides of a lake.