Operation Manual

Diesel fuel flow sensor kit Installation and Operation Manual
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Engine curves are published by the manufacturer
of every engine. If you do not have the curve
for your engine, ask your marine dealer for
the curve.
Usually there will be several curves showing
the different characteristics of your
engine
5 Measuring engine performance
In the above graph:
a The top line shows the maximum power
that the engine is able to provide at each
engine rpm setting - the amount that
would be available if you were to ask
for it. This curve will be published by your
engine manufacturer.
b The lower line shows the propeller load
curve. This is amount of power required
to propel the boat, with the engine doing
those RPM (Remember that usually there
is a gearbox between the engine and
propeller - for all this discussion we will
refer to the RPM of the engine, not the
RPM of the propeller itself).
It takes a set amount of power (hp or kW) to
drive a particular hull at a particular speed, and
it doesn’t matter what the engine is, or how
much extra power might be available, or what
rpm and gearbox ratio you use. It is roughly
equivalent to the power required to tow the
boat through the water. So the lower curve
represents the power that the propeller draws
from the engine, or the load that the propeller
puts onto the engine.
This propeller load curve (the lower line in the
above graph) depends on many things, and is
unique to your boat. The propeller load curve
depends obviously on the diameter and pitch of
the propeller, but also on the hull shape around
5-1 Engine power and propeller curves
- horsepower , fuel consumption etc, each
plotted against engine revs.
The curve we want to discuss is the power
(horsepower or kW) versus engine RPM. The
curve will look something like this:
Power - horsepower
Engine RPM
600 800 1000 1200 1400 1600 1800 2000 2200 2400
Maximum engine RPM
Propeller load
Power