Wartsila ?31DF Series, Product Manual, Page: 18 / 216

Unloading rate, variable speed engines, 750 rpm
Table 2-2 Unloading rate
Emergency,
diesel opera-
tion only
[s]
Fast loading
[s]
Nominal
loading
[s]
Engine load
[% of MCR]
0 N/A
0
100
0 N/A
60
0
Fig 2-3 Unloading rate, variable speed engines, 750 rpm
The propulsion control must include automatic limitation of the load increase rate. If the control
system has only one load increase ramp, then the ramp for a preheated engine should be
used. In tug applications the engines have usually reached normal operating temperature
before the tug starts assisting. The “emergency” curve is close to the maximum capability of
the engine.
Large load reductions from high load should also be performed gradually. In normal operation
the load should not be reduced from 100% to 0% in less than 15 seconds. When absolutely
necessary, the load can be reduced as fast as the pitch setting system can react (overspeed
due to windmilling must be considered for high speed ships).
2-4 DBAE248994
Wärtsilä 31DF Product Guide 2. Operating Ranges