I've built a few ~10-20 hp equivalent electric boat motors and some smaller brushless pod motors like the ones that efoils use -- It's really satisfying enginee

I've built a few ~10-20 hp equivalent electric boat motors and some smaller brushless pod motors like the ones that efoils use -- It's really satisfying engineering work and you have to master so many disciplines along the way: machining/fabrication, CAD, electronics, software, etc... And as with any project of that complexity, you could spend a lifetime just getting interested in a single part of the project.