Something like "L7e"? There are some European classiciations that are theoretically pretty interesting. But you still have to get certified parts, like motor without electric noise and batteries and controller and (I think) still have to test them together in a certified expensive lab. Also windshields.

I wish we had a constitution that costs arising from bureaucratic regulations always have to be paid by the state and never by the citizen. That would fix regulations real quick :D

I suspect that some people manage it because they know people / worked with them and they give them a bit of leeway. So you can get lucky. We have a saying "Where there is no plaintiff, there is no judge".

Well to go slow you only need very little power. But it goes up exponentially much more like with wheels. So you need to design a boat that is long, thin, light and with a large roof surface area. Basically a catamaran or a power trimaran. Then you want glass solar so it's affordable and lasts 20+ years but that is top heavy. But theoretically with the right design solar panels are cheaper than a sail and less complex and easier to maintain than sail+motor+house battery.

But 4-5 knots (~mph) is quite easy. From my amateur calculations 6-7 knots is already hard. I mean those speeds that are sustainable for 24/7 cruising. If you have a large car battery you can go vrooom for a few hours and then slowly recharge over a few days. But my goal is really a slow but seaworthy condomaran.