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 tem-
porarily during transients. Minimum speed is indicated in the diagram, but project specific limitations may
apply.
2.1.1 Controllable pitch propellers
An automatic load control system is required to protect the engine from overload. The load control reduces
the propeller pitch automatically, when a pre-programmed load versus speed curve (“engine limit curve”)
is exceeded, overriding the combinator curve if necessary. Engine load is determined from measured shaft
power and actual engine speed. The shaft power meter is Wärtsilä supply.
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.
Figure 2.1 Operating field for CP Propeller, 450 kW/cyl, rated speed 750 rpm
8 Product Guide Wärtsilä 34DF - 3/2012
Product Guide
2. Operating Ranges
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