12-6 Fuel consumption curves
A fuel consumption curve shows fuel consumption (fuel used per unit of distance travelled) and boat speed as a function of engine RPM. Fuel consumption curves require engine RPM, which requires SmartCraft™ or diesel sensors to be installed. Fuel consumption curves are powerful tools for assessing boat performance in different conditions and for helping you to run at the most economical speed and trim for the conditions.
12-6-1 Making a fuel consumption curve
To make a fuel consumption curve you will need to run the boat in a straight line for about 15 minutes using the engine’s full RPM range. For your first curve, choose a calm day with light wind and little current; have a typical load and a freshly cleaned hull. Later, you can make fuel consumption curves for different boat, weather or sea conditions. Compare these with your first curve to see how your boat’s performance changes with conditions.
Making a curve
1Start running the boat in a straight line.
2Choose a speed source for the curve (see section
3Press 
twice, then select Fuel.
4Select Fuel consumption curve, then select New.
5Enter the comfortable maximum RPM you know you can achieve for the engine rather than the maker’s value.
6The 657 then asks you to set the minimum RPM. Set the throttle to idle; on a multi engine boat set all engines to about the same idle RPM.
Now, do not change the engine speed. Wait for about 60 seconds for the boat to
stabilise, then press 
. Wait while the fuel computer records the data.
7The 657 then asks you to set the throttle to achieve a vessel RPM. On a multi engine boat set all engines to about the vessel RPM. When the engine RPMs are correct, the Vessel RPM box will turn green.
Now, do not change the engine speed. Wait for about 60 seconds for the boat to
stabilise, ensuring the Vessel RPM box stays
green. Then press 
. Wait while the fuel computer records the data.
8The 657 repeats the above step to record data up to the maximum RPM. Then the 657 asks if you want to save the curve. Select Yes. The fuel computer asks for a name for the curve.
Change the default name if required. Then
press 
. The 657 stores the new curve.
Note: To interrupt making the curve at any time,
press 
.
Northstar Explorer 657 Installation and Operation Manual | 49 |
