Marine Installation Manual
2021-08
6-3
6 Engine Dynamics
6.1 External mass forces and moments
X72DF
Second and
fourth order moments
Second (M
2V
) and fourth (M
4V
) order vertical mass moments are also generated,
although these magnitudes will vary depending on engine type and number of
cylinders. Unless a problematic vessel design leads to unfavourable vibration,
there is normally no cause for concern for engines with 7 cylinders or more.
However, 5- and 6-cylinder engines are known to generate high magnitudes of
unbalanced second order vertical mass moments (M
2V
) and should therefore be
carefully considered. Consequently, for 5- and 6-cylinder engines WinGD
strongly recommends that the impact of the second order vertical mass moment
on the vessel is carefully checked. In cases where the investigation reveals a pos
-
sible problem, WinGD recommends to consider the installation of one of the fol
-
lowing countermeasures, designed to reduce the effects of second order vertical
mass moments to acceptable values.
6.1.2
Countermeasures for second order vertical mass moments
WinGD strongly recommends the use of either of the following countermeasures
for 5- and 6-cylinder engines:
•
Engine-fitted electric balancer(s) (iELBA)
•
An electrically-driven compensator, fitted to the ship’s structure
These countermeasures should also be considered for other cylinder number en
-
gines if the second order vertical mass moments (M
2V
) surpass the necessary
limits. However, suitability will vary for different engines and vessel design, as
well as the status of the project, i.e. still in design phase, or retrofitting.
Integrated electrical balancer (iELBA)
The iELBA is structure integrated into the engine and is installed on the free end
and/or driving end. Each iELBA is comprised of two shafts with counter
-
weights, connected with gear wheels and driven by one electric motor. A fre
-
quency converter electronically controls the electric motor. This frequency
converter and the control system are installed in an electrical cabinet in the con
-
trol room. Alternatively, these items can be installed in the engine room.
Figure 6
-
2 Major components and details of the iELBA
SM-0272
A
1 Gear wheel
2 Counterweight
3 Electic motor
4 Shaft
5 Bearing
6 Housing
1
2
2
1
4
4
A-A
3
6
A
5
