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

Ref.: 391/09 and 520/09
Sig. wave length 113 m
Period 8.5 s
Head sea
BSU
Bundesstelle für Seeunfalluntersuchung
Federal Bureau of Maritime Casualty Investigation
Beam sea
Beam sea
Vessel
Figure 41: Polar coordinate diagram up to 12 kts, period 8.5 s – FRISIA LISSABON
On the above three diagrams, the different speeds and courses up to a roll angle of
30° are shown with the corresponding periods of 8.5 s to 9.5 s for the significant
wave lengths of 113-141 m.
Certain parallels with the accidents involving the CCNI GUAYAS and the CHICAGO
EXPRESS can be seen in the polar coordinate diagrams. Parametric rolling is not
dominated and resonances are not visible, therefore, the cases are comparable.
However, in the case of the FRISIA LISSABON a large angle range is present in
which large roll angles do not occur with such long waves. The calculations fit very
well with the statements. The accident occurred in a head sea at an encounter angle
of 60°, which equates to an angle of 120° on the radial axis in the above polar
coordinate diagram. However, it also reveals that the accident could have been
avoided had the vessel been steered into the sea, which was not possible owing to
the draught and fairway conditions leading up to the scene of the accident. Due to
the high level of swell, the weather situation was worse than during the accidents off
Hong Kong. The calculations relating to the FRISIA LISSABON show clearly that the
rolling of the vessel could have been significantly minimised and the accident thus
avoided if it had been possible to steer the vessel directly into the sea at a sufficient
speed of about 5 kts. However, the data from the polar coordinate diagrams are not
available in the required stability information on board since such calculations are not
made in this regard. Accordingly, the crew had no knowledge of this information. The
frequency distribution of the transverse acceleration on the bridge at a speed of 5 kts
is shown on Figure 42 below.
_____________________________________________________________________________________________________
Page 52 of 71