1.5Kw electric outboard design

[vax]

This thread started here: viewtopic.php?f=39&t=33547
I don't want to hijack other's threads, so I made new one.
The goal of this project is to design, build and test open-source electric outboard.
Motor: KD 63-18L Brushless Outrunner 259Kv
Gearbox: taken from Audi A4 starter motor
Propeller: taken from old 8hp Veterok outboard (14mm shaft)
The middle part is made of stainless steel and will have 18mm stainless tube for hull mounting.
Motor cover is made of POM plastic and gearbox rear part (not in pictures yet) will be aluminium or stainless steel.
Seams are connected with 70x1.5mm threads, fixed and sealed with urethane glue. I tried different O-ring solutions, but they needed somewhat bulky bolt connections, that I feeled weren't streamlined enough...

[Gödel]

Since boat drag goes up steeply with boat speed I'd think you'd want a motor that has constant torque so the motor hp peaks at the highest RPM but I couldn't readily find a torque/speed curve for this motor.