Electric boats are not something new. Pre-nuclear military submarines were electric with batteries charged by diesel generators. There are some industrial boats that use electric motors powered by diesel generators. Same for freight trains which have been using that configuration for many years.

A substantial generator is required for a large electric power boat, no way around it. It may not need to run full time if there’s a battery, but it would still need to supply the bulk of consumed electrical power. Not really any environmental benefit. Though there are some other benefits in terms of operating costs.

It’s possible to go all electric without a combustion powered generator on a sailboat. That’s feasible and you don’t need a $10M boat to do it, can be done with any sailboat. Though one thing is a boat must have a reliable motor to be seaworthy. You’d still need a generator backup. In that article they state the featured boat does have one. It would have to support the full electrical load of motor, charging, and accessory so I’d expect it to be pretty hefty.

The title of that article is a fallacy really. Sailboats are environmentally friendly anyway. Doesn’t matter if they have an internal combustion engine or electric motor. You only use the motor in situations where you can’t sail such as tight channels or doldrums. That’s infrequent enough to be negligible. Though I have seen people who own sailboats just motor them around all the time. You gotta wonder why buy a sailboat if you’re just going to motor everywhere, but people do it.