Requirements for the vessels operation at heavy-lift cargoes carriage

Abstract

The approaches used by different classification societies to standardize calculated acceleration under ship motion during heavy lift cargoes transportation are analyzed in the paper. The methods of estimating the efficiency of securing devices of “non-standardized cargoes” carried on ships are investigated. The analysis of the parameters taken into account in determining the design accelerations at ship motion is carried out. Five representative vessels, which had previously carried heavy lift cargoes under different conditions, are selected. Computer modelling of these vessels motion at different course angles is performed in “SafeSea” programme, and calculated (conditional) amplitudes of motion regulated by the Rules of the Russian Classification Society are determined by “Stabedit” programme. The forced and own periods of onboard rolling are calculated in the specialised software complex “Anchored Structures” at variation of wave modes, loading states and values of metacentric height. The calculation results for representative vessels have shown a satisfactory matching of own and forced rolling periods. It is noted that in the range of 1.5 m ≤ h3 % ≤ 4.5 m for the considered intervals of metacentric height, in most cases the forced rolling periods are slightly longer than the own ones. Based on the results of the research, the recommendations for determination of rolling amplitudes of inland and mixed navigation vessels of “P”, “O”, “M”, “O-PR”, “M-PR”, “M-SP” classes carrying heavy lift cargoes are given. The proposals on standardised design acceleration at motion of a ship carrying heavy lift cargo are also given for the mentioned classes of ships. The results of the research are included in the draft Guidelines for the assignment of design acceleration at rocking of mixed (river-sea) and inland navigation vessels and safety margins of heavy lift cargoes securing systems, developed for the Russian Classification Society