I would suggest you read the thread by Harry Smith on his Sea Hornet, which sounds very similar to your model. **LINK**

In my opinion Harry tends to go for the hotter end of motor/prop/battery combinations but it's a good place to start!

Dave M

If you are trying to chose a suitable motor for a particular kit, it would help us to know the name of the kit…

Almost all kits come with some motor recommendations. Have you checked the instructions? 

Edited By Dodgy Geezer on 12/04/2016 13:53:57

With any brushless motor, inrunner or outrunner, it isn't the rotating bit that needs cooling, it is the static bit with the coils on it. With an inrunner, a coil works because the coils are outside, but for an outrunner a flat plate added to the motor mount does the job just as well. OTOH if the right combination of motor and prop is fitted, no cooling should be needed unless there is a strong, if irrational, need to have a source of potential leaks into the hull.

An inrunner motor is physically like a brushed motor.
An outrunner had the outer case rotating with the shaft.This means that you cannot put a coil around it.

Inrunner usually rotate very fast indeed, and are good for racing boats. Outrunner run slower with more torque, and are usually better for sports boats like yours. The one you have picked is an outrunner.

It looks good and powerful – perhaps too powerful, and certainly rather expensive for me.  I note it has a 5mm shaft –  I would tend to go with a 4mm shaft and a 4mm prop-shaft – perhaps  something like this, which should provide lively but not extreme performance:

http://rclife.co.uk/Brushless-Motors/Brushless-Outrunner-Motors/C3548-1100KV-Brushless-Outrunner-Motor?sort=p.price&order=ASC

Brushless motors are odd things – they have no brushes, and brushes tend to limit the power you can put into a motor. Without brushes, you can keep putting more and more power into a motor until it melts. So specifying the maximum power a brushless motor can develop depends rather a lot on the cooling you can provide.

Outrunners tend to cool themselves better than inrunners, and for most sports boats the trick is to run the motor at a sufficiently low power to mean that extra cooling is not needed. The motor you picked, for instance, can take around 40A at 15v – I'm guessing you might think of running it at 10A/7.2v?  100W should be fine for an Aerokits  River Police, though I would defer to the motor specialists for a better guess.  The motor you picked is 600W max – my other suggestion is 500W…

I would think you would not need to cool the motor if running at 7-10v.  Just make sure that it's in a reasonable-sized engine compartment, and perhaps allow a little ventilation? If you need to cool an outrunner, it's an odd exercise – the outside rotates and there's a small section which stays static and is used to clamp it to the motor mount. The motor mount itself is then cooled 

Edited By Dodgy Geezer on 12/04/2016 23:30:01

A. That is a good question and one which depends on so many things that there is no easy answer. I would get an ESC rated above the motors advertised maximum current draw and then use a wattmeter on the boat to actually check the actual current consumption physically. You will not be able to calculate the current draw by using maths.

It is more likely that the ESC will be the thing that needs cooling if it is 40, 50 or even 60A. A fuse here is essential with such large currents. A wattmeter should be purchased straight away if tinkering with motors this powerful, and an array of props also will be required, two blade plastic S and X pitch will do nicely, to get the best speed/power consumption mix.

Ashley

Air ESCs rarely have reverse since planes rarely need to go in reverse. Truck ESCs usually have reverse, but often have a brake facility on the way to reverse. In a boat, reverse is the brakes and when you want to avoid denting a concrete bank, you want it in a hurry, no faffing about with brakes that only exist in theory.