Maximum Continuous Rating Layout Diagram

are shown in percentage scales. The scales are logarithmic which means that, in this diagram, exponential curves like propeller curves (3rd power), constant mean effective pressure curves (1st power) and constant ship speed curves (0.15 to 0.30 power) are straight lines. The constant ship speed lines, shown at the uppermost part of the diagram, indicate the power required at various propeller speeds in order to keep the same ship speed, provided that, for each ship speed, the optimum propeller diameter is used, taking into consideration the total propulsion efficiency.

An engine's layout diagram is limited by two constant mean effective pressure lines L1-L3 and L2-L4, and by two constant engine speed lines L1-L2 and L3-L4. The L1 point refers to the engine's nominal maximum continuous rating (mcr). Based on the propulsion and

1390 2085 2780 BHP/CYL

Figure 10.2 Performance curves for S60MC engine

1390 2085 2780 BHP/CYL

Figure 10.2 Performance curves for S60MC engine engine running points, the layout diagram of a relevant main engine can be drawn in. The specified mcr point (M) must be inside or on the limitation lines of the layout diagram; if not, the propeller speed has to be changed or another main engine model must be chosen. It is only in special cases that point M may be located to the right of line L1-L2.

The specified mcr is the maximum rating required by the yard or owner for continuous operation of the chosen engine. Point M can be any point within the layout diagram. Once the specified mcr point has been selected, and provided that the shaftline and auxiliary equipment are dimensioned accordingly, that point is now the maximum rating

Engine speed, % of L1

Engine speed, % of L1

Line 2 Propulsion curve, fouled hull and heavy weather (heavy running)

Line 6 Propulsion curve, clean hull and calm weather (light running)

MP Specified MCR for propulsion

SP Continuous service rating for propulsion

PD Propeller design point

HR Heavy running

LR Light running

Figure 10.3 Ship propulsion running points and engine layout for S60MC model at which an overload of 10 per cent is permissible for one hour in 12 hours. The continuous service rating (S) is the power at which the engine is normally assumed to operate; point S is identical to the service propulsion point (SP) unless a main engine-driven shaft generator is installed.

All MC engines can be delivered to comply with the IMO speed-dependent NOx emission limits for the exhaust gas, measured according to the ISO 8178 test cycles E2/E3 for heavy duty diesel engines. NOx emissions from a given engine will vary according to the engine load and the optimizing power. Specific fuel consumption (sfc) and NOx emission levels are interrelated parameters and an engine offered with both a guaranteed sfc and the IMO NOx limitation will be subject to a tolerance of 5 per cent on the fuel consumption. (See also the chapter on Exhaust Emissions and Control.)

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  • awate isaias
    Is specified continuous maximum rating same as maximum continuous rating ?
    3 years ago

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