MAN B&W 17.02
Page 3 of 3
MAN Diesel
198 39 250.5MAN B&W S70MC/MC-C/MEC/MEGI, L70MC-C/MEC,
S65MC-C/MEC/MEGI, S60MC/MC-C/MEC/MEGI,
L60MC-C/MEC, S50MC/MC-C/ME-C/ME-B, S46MC-C/ME -B,
S40MC -C/ME B, S35MC/MC -C/ME- B, L35MC, S26MC
178 16 787.0
1st order moments act in both vertical and hori-
zontal direction. For our twostroke engines with
standard balancing these are of the same magni-
tudes.
For engines with five cylinders or more, the 1st
order moment is rarely of any significance to the
ship. It can, however, be of a disturbing magnitude
in fourcylinder engines.
Resonance with a 1st order moment may occur
for hull vibrations with 2 and/or 3 nodes. This
resonance can be calculated with reasonable ac-
curacy, and the calculation will show whether a
compensator is necessary or not on fourcylinder
engines.
A resonance with the vertical moment for the 2
node hull vibration can often be critical, whereas
the resonance with the horizontal moment occurs
at a higher speed than the nominal because of the
higher natural frequency of horizontal hull vibra-
tions.
Balancing 1st order moments
As standard, fourcylinder engines are fitted with
1st order moment balancers in shape of adjust-
able counterweights, as illustrated in Fig. 17.02.02.
These can reduce the vertical moment to an insig-
nificant value (although, increasing correspond-
ingly the horizontal moment), so this resonance is
easily dealt with. A solution with zero horizontal
moment is also available.
1st order moment compensators
In rare cases, where the 1st order moment will
cause resonance with both the vertical and the
horizontal hull vibration mode in the normal speed
range of the engine, a 1st order compensator can
be introduced as an option, reducing the 1st order
moment to a harmless value.
Adjustable
counterweights
Adjustable
counterweights
Fixed
counterweights
Fixed
counterweights
Aft
Fore
Fig. 17.02.02: Examples of counterweights
Since resonance with both the vertical and the
horizontal hull vibration mode is rare, the standard
engine is not prepared for the fitting of 1st order
moment compensators.
Data on 1st order moment compensators and
preparation as well as options in the Extent of De-
livery are available on request.
1st Order Moments on 4cylinder Engines
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