This is a function of battery capacity, boat performance and power setting. A typical QuietTorque system will have approx. 60 minutes of run time at full power.  If you use the sizing model of replacing the diesel with an equal powered QuietTorque  system and match the weight of the old motor, fuel tank, fuel, starter battery, and exhaust system, you will see about 15 to 20 NM range under battery power alone.  Go slow and go long, Go Fast and you severely limit your range. As a rule of thumb, every 1.0 – 1.5 knot increase in speed requires a doubling of power.