Man B&W S50ME-B9.3-TII, Project Manual

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MAN B&W 2.04
Page 4 of 9
MAN Diesel
198 69 93-5.3 MAN B&W MC/MC-C/ME/ME-C/ME-B/-GI-TII engines
Extended load diagram for ships operating in extreme heavy running conditions
When a ship with fixed pitch propeller is operat-
ing in normal sea service, it will in general be
operating in the hatched area around the design
propeller curve 6, as shown on the standard load
diagram in Fig. 2.04.02.
Sometimes, when operating in heavy weather, the
fixed pitch propeller performance will be more
heavy running, i.e. for equal power absorption of
the propeller, the propeller speed will be lower
and the propeller curve will move to the left.
As the low speed main engines are directly cou-
pled to the propeller, the engine has to follow the
propeller performance, i.e. also in heavy running
propeller situations. For this type of operation,
there is normally enough margin in the load area
between line 6 and the normal torque/speed limi-
tation line 4, see Fig. 2.04.02. To the left of line 4
in torquerich operation, the engine will lack air
from the turbocharger to the combustion process,
i.e. the heat load limits may be exceeded and
bearing loads might also become too high.
For some special ships and operating conditions,
it would be an advantage  when occasionally
needed  to be able to operate the propeller/main
engine as much as possible to the left of line 6,
but inside the torque/speed limit, line 4.
Such cases could be for:
• ships sailing in areas with very heavy weather
• ships operating in ice
• ships with two fixed pitch propellers/two main
engines, where one propeller/one engine is de-
clutched for one or the other reason.
The increase of the operating speed range be-
tween line 6 and line 4 of the standard load dia-
gram, see Fig. 2.04.02, may be carried out as
shown for the following engine Example with an
extended load diagram for speed derated engine
with increased light running.
Extended load diagram for speed derated en-
gines with increased light running
The maximum speed limit (line 3) of the engines is
105% of the SMCR (Specified Maximum Continu-
ous Rating) speed, as shown in Fig. 2.04.02.
However, for speed and, thereby, power derated
engines it is possible to extend the maximum
speed limit to 105% of the engine’s nominal MCR
speed, line 3’, but only provided that the torsional
vibration conditions permit this. Thus, the shaft-
ing, with regard to torsional vibrations, has to be
approved by the classification society in question,
based on the extended maximum speed limit.
When choosing an increased light running to be
used for the design of the propeller, the load dia-
gram area may be extended from line 3 to line 3’,
as shown in Fig. 2.04.03, and the propeller/main
engine operating curve 6 may have a correspond-
ingly increased heavy running margin before ex-
ceeding the torque/speed limit, line 4.
A corresponding slight reduction of the propel-
ler efficiency may be the result, due to the higher
propeller design speed used.