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Northstar M121/M84 Installation and Operation Manual 51
13-6 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 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 for the
conditions.
13-6-1 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 13-5-1). Normally choose Water
speed to measure the boat’s potential
performance.
3 Press
MENU
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 M121/M84 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
ENTER
. Wait while the fuel
computer records the data.
7 The M121/M84 then asks you to set the
throttle to achieve a target RPM. On a multi
engine boat set all engines to about the
target RPM. When the engine RPMs are
correct, the Target RPM box will turn green.
Now, do not change the engine speed.
Wait for about 60 seconds for the boat to
stabilise, ensuring the Target RPM box stays
green. Then press
ENTER
. Wait while the fuel
computer records the data.
8 The M121/M84 repeats the above step to
record data up to the maximum RPM. Then
the M121/M84 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
ENTER
. The
M121/M84 stores the new curve.
Note To interrupt making the curve at any time,
press
ENTER
.