Not tested it yet. I'm actually going to power it with two 18.5V 5000mAH Lipos, 37 volts in total. (1.28KG). The speed controller is water-cooled. I don't know what the top speed will be but I suspect it will be ridiculously fast! I'll start with a 50mm prop and try out different sizes. Could this potentially be the fastest fireboat in the world? (Motor: Scorpion HK-4035-560) (ESC: Turnigy Marine) (10/10)