A Practical Assessment of Existing Bulk Carrier Local Structural Strength in Relation to the Allowable Hold Mass Curves

A PRACTICAL ASSESSMENT OF EXISTING BULK CARRIER LOCAL STRUCTURAL STRENGTH IN RELATION TO THE ALLOWABLE HOLD MASS CURVES
K Chatzitolios, Bureau Veritas, Greece G de Jong, Bureau Veritas, France Dr JE Kokarakis, Bureau Veritas, Greece SUMMARY The allowable hold mass curves for vessels built after 1998 are mandatory in the loading manual & the loading instrument as per IACS Unified Requirements S1A. The majority of the bulk carriers in service have been constructed before 1998 and generally do not have allowable hold mass curves. Pre-1998 bulk carriers engaged in multi-port operations need to have allowable hold mass curves to control the local strength of the cargo hold structure for the envisaged loading conditions. The curves are produced according to the loading conditions of the approved loading manual as a function of the draught. For the case of an individual hold they are determined by examining bending and shear stresses in floors and girders, as well as buckling stresses in the associated plating. For the case of two adjacent holds the strength of the transverse bulkhead and cross deck is considered as well. The curves can be checked with finite element analysis or other methods to obtain the applicable safety margin. The paper presents a theoretical derivation of the hold mass curves as function of the draught and provides some comparisons with formulations by other class societies and IACS requirements. A practical methodology to determine the hold mass curves when not available is proposed. An interesting application, presented in a case study in the paper, is the determination of the maximum draught as a function of the static still water bending moment at the empty holds. The combination of a hogging hull girder bending moment and hydrostatic pressure at 60 to 70% of the scantling draught may cause severe buckling of the bottom plating and exceed its ultimate strength. A methodology on how to assess this loading condition for holds which are not

References: Intercargo, ‘Intercargo Briefing: Loading Rates’, Rev.0.1, 21 November 2008 Lloyd’s MIU, ‘SeaWay’, May 2009 IACS, ‘Bulk Carriers - Guidance and Information on Bulk Cargo Loading and Discharging to Reduce the Likelihood of Over-stressing the Hull Structure’, Rec. 46, 1997 Bureau Veritas, ‘Rules for the Classification of Steel Ships’, Pt B, Ch 5, Sec 5, [2], April 2009 Journée JMJ, Massie WW, ‘Offshore Hydrodynamics’, First Edition, Delft University of Technology, January 2001 Bureau Veritas, ‘Rules for the Classification of Steel Ships’, Pt B, Ch 5, Sec 4, April 2009 Bureau Veritas, ‘Rules for the Classification of Steel Ships’, Pt B, Ch 5, Sec 3, [2], April 2009 IACS, ‘Harmonised Notations and Corresponding Design Loading Conditions for Bulk Carriers’, UR S25, Rev. 2, July 2004 Bureau Veritas, ‘Rules for the Classification of Steel Ships’, Pt B, Ch 5, April 2009 AUTHORS’ BIOGRAPHIES 4. 5. 6. 7. 8. 9. 7. Kostantinos Chatzitolios currently works in Bureau Veritas as a hull surveyor in the plan approval office (HPO) of Piraeus, Greece. He joined Bureau Veritas in 2005 after obtaining a Diploma in Naval Architecture and Marine Engineering from the National Technical University of Athens. In the four years that he has worked in HPO he has dealt with stability and hull matters of bulk carriers, oil tankers and passenger ships. In the last two years he is specialized in the hull structure of bulk carriers (existing and CSR) and oil tankers. Konstantinos is currently undertaking a Masters degree in Business Administration (International MBA) in the Athens University of Economics and Business. Gijsbert de Jong holds the current position of product manager at Bureau Veritas and is based in the Head Office in Paris. He is responsible for the international business development in the field of container ships and dry bulk carriers, as well as a number of specialised ship types. Gijsbert joined Bureau Veritas in 2001 after obtaining an MSc in Naval Architecture & Marine Engineering from Delft University of Technology. Before moving to Sales & Marketing Management in 2007, he has worked as hull surveyor and department manager for the Bureau Veritas plan approval office in Rotterdam. During this period Gijsbert has built up extensive experience with dry cargo & container ships, dredgers, asphalt carriers, product tankers, reefers & tugs. In his present position he is working closely together with BV’s technical specialists and extensive international network to develop new products and services meeting with the maritime industry’s specific needs. Gijsbert has published technical papers on container ships, bulk carriers, arctic shipping and fuel cell power systems and regularly writes articles for marine industry magazines. Dr John Emmanuel Kokarakis, a 1979 graduate of National Technical University of Athens, he holds PhD (1986) and Masters degrees in Naval Architecture (1983) and Masters in Mechanical Engineering (1984) from the University of Michigan. He worked for over ten years as a consultant undertaking technical problems worldwide. His specialization was in the area of technical investigation of marine accidents. In his capacity as a forensic engineer he participated in the technical investigation of the Exxon Valdez grounding, Sea-crest Capsize, Piper Alpha fire and explosion, Aleutian Enterprise foundering in Alaska as well as many other accidents of less notoriety. The last eleven years he works in Greece, in the area of classification. Having served in the plan approval office of American Bureau of Shipping in Piraeus, he then joined Germanischer Lloyd heading their tanker and bulk carrier team in Greece. He is currently the Technical Director of Bureau Veritas in the Hellenic and Black Sea Region. In his duties Dr. Kokarakis is responsible for the smooth technical operation in the region as well as in the harmonic cooperation with the BV offices worldwide to the benefit of the BV clients in Greece. He was a member of the team which developed the Common Structural Rules.