In boat use, there is no such figure hat really means anything – current drawn at any given voltage depends on the load imposed by the prop. One limiting factor is how much waste energy can be dissipated by the size of can, this heat comes from the inefficiency of the motor converting electric energy into kinetic energy. The inefficiencies creep in with losses due to the air gap in the magnetic path, losses due to the magnetism of the rotating poles changing rapidly and heat from the brushes. And having really strong magnets for the armature fields to push against. And good bearings. Good engineering minimises the losses, Graupner were very good at that.

There will be data sheets somewhere giving performance predictions which are fine in a pure mechanical system, like "how much weight and how high can this crane lift in a given time?", but driving a prop trying to accellerate water is a different world, and is why there is a lot of "Black Art" involved. A motor "can" draw a high current and get away with it if it is spinning fast through a light load – if it is heavily loaded and running inefficiently, more of the energy is converted to heat and the motor cooks even if it is pulling the same current as when spinning fast.

Hopefully someone will have one and know the current draw in his particular circumstances. If it happens to be the same type of boat as yours and it works OK, you have the assurance that your should work. Otherwise, there is empirical testing to be done involving a motor mount, prop shaft, various propellers, an ammeter and a bucket of water and observing how hot the motor gets.

15 amps approx. with a 30 mm 3 blade plastic prop

Edited By John W E on 15/02/2019 15:50:27

Edited By John W E on 15/02/2019 16:03:52