@Jezza: Great, then let us know the detailed figures
@PowerGlider: The cooling surface on the outside is plenty. Let it run through the motor would make it expensive due to potting and also vulnerable to the process. Saltwater is very aggressive, especially over time, bearings and all the other unprotected surfaces in contact may face severecorrosion.
The back iron depends on the winding pattern, so you can minimize this Halbach is in my opnion not necessary. If you have deeper questions, you can ask me directly
@beonwater: Both the magnets, and the rotor are custom made. You can get them from prototyping companies, but it’s expensive in that way… therefore I asked you all, if we can increase the quantity, the price gets lower.