2. Operating Ranges
2.1 Engine operating range
Below nominal speed the load must be limited according to the diagrams in this chapter in
order to maintain engine operating parameters within acceptable limits. Operation in the
shaded area is permitted only temporarily during transients. Minimum speed is indicated in
the diagram, but project specific limitations may apply.
2.1.1 Controllable pitch propellers
The engine load must be limited according to the diagram below when operating below nominal
speed, in order to maintain engine operating parameters within acceptable limits. Operation
in the shaded area is permitted only temporarily during transients to permit smooth overload
control.
Note that project specific vibration calculations may result in higher minimum speed than in
the diagram below.
The propulsion control must also include automatic limitation of the load increase rate.
Maximum loading rates can be found later in this chapter.
The propeller efficiency is highest at design pitch. It is common practice to dimension the
propeller so that the specified ship speed is attained with design pitch, nominal engine speed
and 85% output in the specified loading condition. The power demand from a possible shaft
generator or PTO must be taken into account. The 15% margin is a provision for weather
conditions and fouling of hull and propeller. An additional engine margin can be applied for
most economical operation of the engine, or to have reserve power.
Fig 2-1 Operating field for CP Propeller
Wärtsilä 31 Product Guide - a1 - 18 October 2016 2-1
2. Operating RangesWärtsilä 31 Product Guide
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