Examination of the intact stability and the seakeeping behaviour

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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. 1
Page 1: Dezember 2010 SCHRIFTENREIHE SCHIFF
Page 5: 1st Examiner: Prof. Dr.-Ing. Stefan
Page 9 and 10: Contents List of Figures List of Ta
Page 11 and 12: Contents A.14 Vessel No. 14 . . . .
Page 13 and 14: List of Figures 2.1 Calculation mod
Page 15 and 16: List of Tables 3.1 Accident situati
Page 17: Nomenclature Symbol Unit Meaning A
Page 21 and 22: 1.2 Following objectives for the di
Page 23 and 24: 2 Theory 2.1 Description of the uti
Page 25 and 26: 2.1 Description of the utilised sea
Page 27 and 28: 2.1 Description of the utilised sea
Page 29 and 30: 2.2 Environmental conditions period
Page 31 and 32: 3 Data input The thesis is written
Page 33 and 34: 3.6 Free surface correction 3.6 Fre
Page 35 and 36: 3.10 Bridge height 3.10 Bridge heig
Page 37 and 38: 4 Examination For each vessel the s
Page 39 and 40: 4.2 Vessel No. 02 4.2 Vessel No. 02
Page 41 and 42: 4.3 Vessel No. 03 ˆ The documented
Page 43 and 44: 4.5 Vessel No. 05 accident situatio
Page 45 and 46: 4.6 Vessel No. 06 4.6 Vessel No. 06
Page 47 and 48: 4.7 Vessel No. 07 ˆ The stability
Page 49 and 50: 4.9 Vessel No. 09 Figure 4.16: Tran
Page 51 and 52: 4.10 Vessel No. 10 4.10 Vessel No.
Page 53 and 54: 4.11 Vessel No. 11 ˆ The limiting
Page 55 and 56: 4.13 Vessel No. 13 Figure 4.24: Tra
Page 61 and 62: 5 Evaluation Based on the determina
Page 63 and 64: 5.3 Recommendations accelerations s
Page 65 and 66: 6 Detailed examination The evaluati
Page 67 and 68: 6.1 Variation of the GM values acce
Page 69 and 70:
6.2 Rolling behavior of the large v
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7 Conclusions Summing up the result
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A Vessel data A.1 Vessel No. 01 Tab
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A.3 Vessel No. 03 A.3 Vessel No. 03
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A.11 Vessel No. 11 A.11 Vessel No.
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B Variation of the bilge keel area
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C Variation of the ship's speed 16
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Bibliography [1] BSU; Federal Burea
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