WinGD X72DF, Руководство по установке

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Marine Installation Manual 2021-08 2-5
2 Engine Power and Speed
2.4 Power range
X72DF
Light running margin
The Light Running (LR) margin (see Figure 2 - 2,  2-4 ) is added to compensate
for the expected change in speed to relative power, caused by the fouling and the
deterioration of the vessel over time. For a given engine power output, the light
running propeller (Line 8) operates at a certain percentage of higher propeller
speed compared to the nominal engine characteristic (Line 7). The light running
margin is agreed upon between the shipyard and the ship owner. The margin de
-
pends on the hull and the propeller cleaning interval, as well as the operation
route which will affect the rate of deterioration (e.g. speed, location, shallow
water, etc.)
Typically, the light running margin is specified in the range of 4 to 7 %. However,
additional power/engine speed allowance must be provided for the Power
Take-Off (PTO) installations (see section
2.6,

2-10 ).
Continuous service rating
The Continuous Service Rating (CSR) is also known as the Nominal Operation
Rating (NOR) or the Nominal Continuous Rating (NCR). Point A represents the
power and propeller speed of a ship operating at contractual service speed in
calm seas with a new clean hull and propeller. On the other hand, the same ship
at the same speed, under service conditions with aged hull and under average
weather conditions, requires a power/speed combination according to point B.
In that case, point B is the CSR point.
Engine margin
The Engine Margin (EM) is the relative power (in percentage) which remains at
CSR. Most owners specify the contractual ship’s loaded service speed at 85 to
90% power of the contracted maximum continuous rating. Different selections
are possible. This remaining power, the EM (e.g. 10 to 15%), can then be used to
catch up with delays in schedule.
This margin is deducted from the CMCR. Therefore, the 100 % power line is
found by dividing the power at point B by the selected percentage (e.g. 85 to
90%) of CSR power. The graphic approach to find the level of CMCR is illus
-
trated in Figure 2 - 2,  2-4 .
Contracted maximum continuous rating
The Contracted Maximum Continuous Rating (CMCR) is also known as the Rx
or the Specified Maximum Continuous Rating (SMCR). The CMCR is the point
obtained by applying the margins (SM and EM) to the propeller curves. The cal
-
culated CMCR point can be selected freely within the entire engine rating field.
NOTE
The shipbuilder has the responsibility to determine a light running
margin. This light running margin must be sufficiently small so that the
power range limits on the right side of the nominal propeller character -
istic (Line 7) are reached under any service condition (see Figure 2 - 3,

2-6 ).