Hi Marc,
there's a misunderstanding: theory and practical measurements are completely identical - there is no difference at all.
The only thing which really differs (and this is what I'm always repeating!!) are the motor designations of the manufacturers.
When you use the same propeller on the same model you will
ALWAYS get the same power consumption, no matter which motor you use. (Maybe there's a slight difference because of the different degree of efficiency of the two motors - but that's all!)
Try a 200 watts motor which has enough torque to move your propeller. And then next try a 1500 watts motor with the same degree of efficiency and the same propeller: the power consumption and the power output will remain exactly(!!) the same with both motors. And this is absolutely logical: why should the same boat with the same propeller need
more power when you install a bigger motor? This is what the theory says - and what the praxis confirms.
525 watts does
NOT mean: your boat is powered by 525 watts. It also does
NOT mean: your boat needs 525 watt to run maximum speed. It
just says: the motor consumes up to 525 watt maximum input power (= 47,3 amperes on 3S) if it is stressed up to it's permitted limit (e.g. with a huge prop).