SUB-COMMITTEE ON STABILITY AND LOAD LINES AND ON ...

Ref.: 391/09 and 520/09
BSU
Bundesstelle für Seeunfalluntersuchung
Federal Bureau of Maritime Casualty Investigation
The following table shows the respective tank fillings and the resulting maximum roll
angle:
Filling in t 10 50 100 150 200 250 300
Roll angle 38.0 37.2 36.9 36.3 35.9 35.5 35.0
in degrees
Filling in t 350 400 450 500 550 600 650
Roll angle 34.7 34.3 34.0 33.8 33.1 32.6 33.4
in degrees
Figure 30: Roll angle depending on the tank filling
The maximum effect is achieved with a filling of 600 t. This is equivalent to a
reduction in roll angle of about 2-3° compared to the roll angles present on the day of
the accident. Overall, with a partial tank filling the roll angle reduces up to that point
and then starts to increase again. The 600 t of ballast water would cause the centre
of gravity to shift downward by 28 cm, due to which the stability would increase. The
acting accelerations were calculated for this maximum reduction in roll angle with
ballast water of about 600 t:
Figure 31: Transverse accelerations on the bridge influenced by the tank
The histogram on the left shows the influence of the partially filled tanks and the one
on the right without a tank. It can be seen on the left histogram that the calculated
maximum accelerations decrease to about 10 m/s² compared to that of the accident
of 12 m/s². This is also equal to the reduction in roll angle calculated above in
qualitative terms. Furthermore, it can be seen clearly how a shift in the frequency
distribution of the accelerations to overall smaller values occurs, the larger
acceleration values are now reached in much fewer cases.
On the whole, this is logical because the tank can only minimise certain exciting
moments. If these are exceeded, in somewhat higher waves for example, then high
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