This section is available on request - MAN Diesel & Turbo

MAN B&W 17.02
1st Order Moments on 4�cylinder Engines
1st order moments act in both vertical and horizontal
direction. For our two�stroke engines with
standard balancing these are of the same magnitudes.
For engines with five cylinders or more, the 1st
order moment <strong>is</strong> rarely of any significance to the
ship. It can, however, be of a d<strong>is</strong>turbing magnitude
in four�cylinder engines.
Resonance with a 1st order moment may occur
for hull vibrations with 2 and/or 3 nodes. <strong>Th<strong>is</strong></strong>
resonance can be calculated with reasonable accuracy,
and the calculation will show whether a
compensator <strong>is</strong> necessary or not on four�cylinder
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 vibrations.
Balancing 1st order moments
As standard, four�cylinder engines are fitted with
1st order moment balancers in shape of adjustable
counterweights, as illustrated in Fig. 17.02.02.
These can reduce the vertical moment to an insignificant
value (although, increasing correspondingly
the horizontal moment), so th<strong>is</strong> resonance <strong>is</strong>
easily dealt with. A solution with zero horizontal
moment <strong>is</strong> also <strong>available</strong>.
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.
MAN B&W S70MC/MC-C/ME�C/ME�GI, L70MC-C/ME�C,
S65MC-C/ME�C/ME�GI, S60MC/MC-C/ME�C/ME�GI,
L60MC-C/ME�C, S50MC/MC-C/ME-C/ME-B, S46MC-C/ME -B,
S40MC -C/ME B, S35MC/MC -C/ME- B, L35MC, S26MC
MAN Diesel
Page 3 of 3
Since resonance with both the vertical and the
horizontal hull vibration mode <strong>is</strong> rare, the standard
engine <strong>is</strong> 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 Delivery
are <strong>available</strong> on request.
Adjustable
counterweights
Aft
Fixed
counterweights
Fig. 17.02.02: Examples of counterweights
Fore
Adjustable
counterweights
Fixed
counterweights
178 16 78�7.0
198 39 25�0.5