Examination of the intact stability and the seakeeping behaviour

7 Conclusions
Summing up the results from the thesis can be done by stating: All examined container vessels
have a signicant problem with their seakeeping behavior in the ballast arrival loading condition.
Within this examination, all vessels reach very high transversal accelerations on their bridges.
This problem with excessive accelerations occurs for loading conditions, where the vessels have
no or only few cargo on board resulting in rather small drafts and thus high stability values. For
twelve of the analysed vessels the ballast arrival loading condition is most critical while for the
three largest vessels the most critical condition occurs at higher drafts at the FP.
Further, this thesis proves that the named problem is not caused by the high stability values
only. Other factors like the ship's trim or the ship's hull form also have a great inuence on the
seakeeping behavior. Therefore a simple approach like the determination of a single upper limit
for the GM does not seem to be a feasible approach to avoid such accidents in the future.
Particularly due to distinctive nonlinear eects, mainly on the roll motion, the seakeeping
behavior can denitely not be calculated with simple linear approaches. Therefore it is recommended,
that the seakeeping behavior for each single loading condition should be evaluated
during the early design process by the application of numerical methods, which are capable to
simulate these nonlinearities. In this way it can be identied, whether a ship's ballast arrival
loading condition should be stated to be a seagoing condition or if there is an increased risk
of accident. With such methods, it is possible to reproduce the behavior of the ships during
real accidents very well (refer to the accident reports [1][2][3]). Thus the seakeeping calculations
performed for this thesis, also represent well the real seakeeping behavior of the analysed vessels
and are adequate to estimate the risk of encountering an accident.
Having gained this knowledge, it becomes obvious that there is a need for establishing mandatory
regulations for the determination of the seakeeping behavior and to increase the safety on
the bridges for the crew.
Furthermore, since the excessive stability alone is not responsible for the accidents, the operating
could be considered as main cause. This is not reasonable, because the crew of all vessels
within the analysed accident situations [1][2][3] followed a good seamanship for the behaviour
in heavy seas. This behavior, which consists mainly of heading into the waves at slow speeds,
is the result of long lasting experiences on vessels in heavy sea. Following this procedure it is
ensured, that vessels keep their manoeuvrability and do not face high slamming loads on the
bow structure as well as green water on deck. These eects can cause severe damages on the
ship's hull structure and on the stowed containers on deck.
Concluding, it has to be stated, that container vessels facing the described circumstances
generally have a highly increased risk of encountering accidents and it is strongly recommended
to perform reliable calculations during the ship design and the approval process in order to
identify operational constraints and thus prevent probable accidents.
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