Quote:
Originally Posted by ET2SN
Well, to go even deeper- 
Now imagine the stress of reversing the field while the motor is running near its rated speed (at some point you'll also block the rotor for a couple of seconds).  |
Add the additional force of the screw as it is moving through the water thus making want to continue to spin in the same direction. You are adding to even MORE counter torque than just stopping the shaft and reversing it. Take your blocked rotor test and double the amount of stress due to counter electric motive force.