Additional cooling of outrunner motors?

Maybe a dumb question, but for for those whom not plan to have direct water cooling on outrunners, have understood heat might be an issue. The question is, what if You would drill holes(through the cover) between the magnets, would that have an impact the electrical function/efficiency on the motor or not?
Holes as such would probably not much increase the airflow into the motor but with some help of a small “catchers” some airflow effect can be achieved?

heat comes from the copper on the rotor, It might be easier and more effective to put a small propeller on the shaft to help dissipate heat in the case.
Also space beetween magnets is really small so drilling between might be a challenge, and if you succeed you might have to balance the rotor…

Yes, you are right, space is tight and balancing might be needed. The propeller is a good idea. The issue is that as You say, the heat is in the rotor, so what we would need to have a improved airflow and change of air inside the casing, around the rotor, most solutions basically cools down the outer side only.

If would be able to make cut open some of the the narrow space space(not only holes)between the magnets, the rotor would maybe act as an impeller, throwing out the hot air through the narrow openings in the casing and possible improve airflow and cooling?

Balancing can be got by drilling an identical hole on a symetrical point wr to the axis.
2 holes or 4 = better cooling.

How much air do you plan to have inside the enclosure?
What is the mass of this gas?
At which rate do you plan to exchange the air to get rid of e.g. 250W power losses?

Will as first project start with a e surfer, no foil. This means will have the motor inside the board. My plan is to have water cooled engine mount but dont think that will be enough. Have not decided Yet, but think there are several ways of getting rid of the hot air. A closed system would be to have aluminium plates with fins, both inside and outside. Another option is to simply change the air. The combustion engine jet boards must have a huge amount of air coming into the engine compartment, apparently safely, so probably can copy something from there( snorkle?). Getting parts from china takes time, so many delivery errors so far, unbelievable, will take months before can start the build:)

This will be a Very different build… straight axle, one standard propeller, 2 x 6384 120kv with belt drive( 1/1 ratio!) 120kv 7S, 2 x150A budget ESC and probably DIY Lifepo4 32700 battery bank…Throttle will be wired, at least start with that. Will loose a few KG but parts are relative cheap so can afford if i “let the smoke out” :slight_smile: I am fixing two real boats simultaneously so not that much time for this, maybe late autumn ready only.

To the question about how much air, that depends on the cooling design. Hull will be done from 20mm xps and epoxy +cloth, so can adjust the space freely pending on design.