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49Northstar Explorer 657 Installation and Operation Manual
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
1 Start running the boat in a straight line.
2 Choose a speed source for the curve (see
section 12-5-1). Normally choose Water speed
to measure the boat’s potential performance.
3 Press
twice, then select Fuel.
4 Select Fuel consumption curve, then
select New.
5 Enter the comfortable maximum RPM you
know you can achieve for the engine rather
than the maker’s value.
6 The 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.
7 The 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.
8 The 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
.