Hi AndyG Not sure what type of coupling was supplied but I use a common Universal coupling on my 48" Sea Queen and use a brushless 42 size 850Kv water cooled motor of 700 watts and it is happy driving a Prop Shop prop of 42mm at 45 amp on full throttle. Power is from an 11.1v Lipo of at least 2200 mA but Nimhs would work, just not as fast and less duration. My motor is mounted in the main cabin and I have no problem with the prop shaft. Originally designed for IC power so perhaps you have heard of problems when we used such powerful and not so well controlled devices. My model goes on the plane very easily and any more power would make it unstable. Pics attached to show my set up. You can just see the coupling in front of the motor.