Iveco Marine Diesel Engines, Installation Handbook

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MARCH 2004 ENGINE/BOAT CHOICE FACTORS
2.27
MARINE ENGINES INSTALLATION
imum power speed by loading the dynamometric brake, starting from the idling maximum speed
with the accelerator at limit switch, until the maximum power is detected.
This ratio represents the regulator percentage difference at the rated speed.
The curve linking the maximum power value to the null power at the maximum speed is called gap
curve .The gap in IVECO marine engines usually amounts to 10%.
■
Maximum torque speed (n
c
) : it is the speed, or speed interval, at which the engine reaches the
maximum torque. It is measured during the above mentioned tests, starting from the maximum
power with the accelerator in limit switch position and increasing the load of the dynamometric
brake. The higher need for energy makes the engine reduce its running speed in order to obtain
the maximum torque.
The maximum torque speed is usually identified as the condition with the lowest specific con-
sumption. With a speed ranging between the maximum power value and the maximum torque
value the engine has a “stable” behaviour, i.e. it regulates itself to adapt its speed spontaneously to
the load changes.
Cs. Specific consumption - N. Power - n. Engine speed - M.Torque - A. Gap curve.
In marine applications, the typical rule for the power absorption is the square/cube rule depending on
the propeller; the type of hull used greatly affects this rule: in gliding boats, the hull dynamics makes this
rule change to a pattern more similar to that shown in figure 3, where there is a hump corresponding
to the power absorbed to reach the gliding position.
Therefore, on gliding boats it is necessary to install an engine with a great power and torque also at
intermediate speeds.
Figure 1