> for starters you're not bound to islands big enough for an airport.
The competition for that space is seaplanes, including both floatplanes and flying boats, which have been around for a century. Electric versions of those exist, like https://harbourair.com/corporate-responsibility/goingelectri... , and https://el-fly.no/ wants to build an electric amphibious flying boat.
Yes, a ground-effect vehicle has better wing efficiency than an aircraft. However, it has disadvantages, like how it handles waves. A flying boat, for example, only needs to worry about the waves at the departure and arrival locations, which may be in a protected harbor or channel, while a GEV must deal with larger waves between the islands.
See https://en.wikipedia.org/wiki/Ground-effect_vehicle#Advantag... for additional comparisons.
> So what starts small, and touristy
I flew on a seaplane between the US and the Bahamas, https://en.wikipedia.org/wiki/Chalk%27s_International_Airlin... . It was a fun touristy thing, but not touristy enough to maintain a commercial seaplane service.
> On the environmental front I expect the usual "complain about anything new" crowd
Thing is, this isn't new. Ground effect vehicles have been around for decades, the technology is pretty mature, and the problems also pretty well known. If someone cracks that nut - great! - but a lot of people have tried and failed to extend its use outside of some niche areas. That history of failure tends to dampen enthusiasm.
> But it's hard to see how this does more environmental harm than planes or boats.
That calculation is not easy. If you want to minimize environmental harm the most, switch to sailboat. Cook used no fossil fuels to travel to and around Hawaii, and neither did the Polynesians who discovered the place.
If you want to minimize CO2 emissions, ban all inter-island flights and switch to ferries - https://ourworldindata.org/travel-carbon-footprint says ferries emit about 1/7th of the CO2 as short-haul flights.
And there are electric ferries these days, like https://www.electrive.com/2021/03/02/worlds-largest-electric... , though that's not ocean going. See https://electrek.co/2023/01/17/worlds-largest-electric-ferry... for one in the works.