Not knowing your system, I'd suggest checking the actual motor voltages. With 13 - 14 volts from the system, I wouldn't expect more than a volt or two drop in the switches, giving at least 11 volts at the motor. Does the computer drive the motor directly, or is there another black box with the switching transistors? If so, the 6 volts may well be the normal error signal to run the motor.
What's wrong with towing the dingy???