Examination of the intact stability and the seakeeping behaviour

1 Introduction
In the years 2008/2009 the world economic crisis caused a reduction in the number of transported
TEU, due to a signicant decrease in transported goods. Consequently a great number of container
vessels had been laid up or were forced to operate with a small amount of cargo on board.
In this loading condition container vessels have a very high stability. In many cases their vertical
center of gravity is even located below the lightship condition's coordinate. This is due to large
amounts of ballast water in wing and double bottom tanks as well as no or only a small amount
of cargo located at cargo hold bottom. The high amount of ballast water is needed to obtain an
adequate hull and propeller immersion as well as a limitation of the longitudinal bending moments
within the hull structure. In the typical loading conditions with higher amounts of cargo,
less ballast water is needed and the stability is lower. Under the described circumstances, several
accidents have happened to container vessels during the last years. The accidents caused not only
severe damages on ships but also heavily injured and even killed crew members. They have been
thrown through the bridge due to high transversal accelerations caused by heavy roll motions
of the ship. This highlights, that modern container ship designs face some problems concerning
insucient seakeeping behavior. Since several accidents have happened to ships sailing under
German ag, the BSU analyzed them by default. For three of the accidents, the seakeeping
behavior has been examined in detail by order of the BSU at the institute of ship design
and ship safety at the Hamburg University of Technology (TUHH) [1][2][3]. This
thesis shall examine the seakeeping behavior of several typical container vessels in equivalent
environmental conditions.
1.1 Key data of the three examined accidents
The examinations revealed signicant parallels between the accidents. They all happened under
comparable environmental and loading conditions.
ˆ All ships followed the standard procedure for heavy weather. This means, that they head
into the sea at slow speeds to minimize the risk of damaging the ship's bow structure due
to high slamming forces and green water on deck.
ˆ All ships encountered large rolling angles of more than 30 ◦ .
ˆ Due to the excessive stability and the therefore short roll periods of the ships, the high roll
angles resulted in transversal accelerations of up to 14 m /s 2 .
In the following, an overview of the environmental conditions and several ship data for the
three examined accidents is given. More detailed information about the accidents and their
circumstances may be extracted from the respective investigation reports.
1.1.1 Accident of the CMS Chicago Express [1]
ˆ The accident happened on September 24th, 2008 during heavy weather in the South
China Sea near Hong Kong.
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