Exam Question

A ship consumes an average of 70 tonnes of fuel per day on main engines at speed of 17 knots. The fuel consumption for auxiliary purposes is 8 tonnes per day. When 800 nautical miles from port it is found that only 140 tonnes of fuel renmains on boarrd and this will be insufficient to reach port at the normal speed. Determine the speed at which the ship should travel to complete the voyage with 20 tonne fuel remaining.