With that prop that motor is likely to get really hot and over heat the wires and connectors. I think you should check the motor connectors and see if it is still properly solder to the motor wires. Check the connectors on the esc too, battery and motor connectors. Because in my experience there is no way that setup will run more than a 1 1/2 to 2 minutes without melting the solder off the wires causing the connection to brake and make the boat stop. A 445 is too much for that small motor especially on 4s if you want a reliable setup. A graupner k40.5 might be much better for your setup. But I feel the motor is too small in the first place to be running 4s and props above 40 mm.