Examination of the intact stability and the seakeeping behaviour

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6 Detailed examination in tables 6.7 and 6.9, are a higher displacement and therefore a higher draft of about 1.6 m for the second loading condition set. For a vessel of this size, these dierences do not seem remarkable. Nevertheless for one of the rst loading conditions, a moderate maximum transversal acceleration of 5.5 m /s 2 occurs, while for one of the second loading conditions, the value becomes signicantly higher, reaching an extremum of 10 m /s 2 . These maximum accelerations occur for a GM solid ∼ = 9.25 m in both cases. The analysis reveals that signicantly dierent accelerations may occur for similar GM values and just slightly dierent oating conditions. Thus a simple way to decrease the risk of accidents, like the determination of a single upper limit for the GM for example, to limit the excessive stability and decrease the occurring transversal accelerations is not a feasible approach. 56
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. 57
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 and 18:
Nomenclature Symbol Unit Meaning A
Page 19 and 20:
1 Introduction In the years 2008/20
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
Page 71 and 72: 6.2 Rolling behavior of the large v
Page 73: 6.2 Rolling behavior of the large v
Page 77 and 78: A Vessel data A.1 Vessel No. 01 Tab
Page 79 and 80: A.3 Vessel No. 03 A.3 Vessel No. 03
Page 87 and 88: A.11 Vessel No. 11 A.11 Vessel No.
Page 93 and 94: B Variation of the bilge keel area
Page 95 and 96: C Variation of the ship's speed 16
Page 97: Bibliography [1] BSU; Federal Burea
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Examination of the intact stability and the seakeeping behaviour

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