All engine builders provide diagrams for their particular models, from which various running conditions can be determined. The diagrams are assembled from information from engine tests taken under controlled conditions. The diagram for one engine of a range is then used as a standard for all other engines in that range.
Unfortunately there is no standardised format for these diagrams and the engineer must familiarise himself with the chart prepared for the engine with which he is working.
On figure is shown a graphical representation of various brake powers against revs per min and mean effective pressure. Such a diagram may be used by the ship’s staff to determine load/speed areas within which the engine can be operated safely. It should be appreciated that this diagram is not applicable to any particular make or range of engines but simply represents the way that some engine builders display these parameters.
There will also be different diagrams according to whether the engine is direct drive or driving through a CP propeller. On figure is shown a fixed pitch propeller and assumes that the power output varies as the revs3 and that the mean effective pressure varies as the revs2.