Cube purple wont follow cruise speed setting

Once I flip the auto switch my boat will not go cruise speed. I must move the throttle and set the cruise speed manually. Does anyone know why?

Could it be your CRUISE_THROTTLE and CRUISE_SPEED are too different?
https://ardupilot.org/rover/docs/rover-tuning-throttle-and-speed.html#cruise-throttle-and-cruise-speed