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Object and purpose of research. This work was intended to analyse technical solutions that could contribute to power efficiency of in-service fleet in the light of new IMO policy aimed at the mitigation of greenhouse gas emissions from international marine traffic. This is the second publication in the series of articles discussing various aspects of this new IMO policy, as well as shipbuilding challenges that have to be faced in order to meet relevant requirements. Subject matter and methods. This work is an analytical review of available publications on above-mentioned topic. It relies on Krylov State Research Centre experience in the optimization of ship fuel consumption, as well as on the results of IMO correspondence group discussions on power efficiency with participation of Krylov State Research Centre and RS experts. Main results. This paper discusses the efficiency of measures taken all over the world to improve fuel efficiency of ships taking into account the experience of their implementation at the early stage of IMO regulations for greenhouse gas emissions. It is shown that each of these measures might reduce the emissions from global marine traffic by ~5%, which is not enough to achieve the final goal, i.e. 70% reduction in emissions by the year 2050 as compared to 2008. Besides, these measures cannot be implemented in full due to certain limitations. For example, in Russia the main obstacle is that practically all its ships must have an ice class, so they cannot use a whole number of various power-saving devices because of their vulnerability to ice impact. Still, provided that power-saving devices are robust enough, they might prove to be a useful (and sometimes the only possible) way to reduce gas emissions of a ship after several years of service. It is incorporated to the system rating the ships in terms of their emission score assigned as per the new provisions of MARPOL Annex VI adopted in 2021, see Part I of this series. Conclusion. Analysis of power saving measures (along with assessment of their efficiency and applicability to ice-class ships) enables a justified selection of power efficiency enhancement tools for a ship in case its annual Carbon Intensity Indicator (CII) goes beyond IMO thresholds that gradually become more and more stringent in accordance with new provisions of MARPOL Annex VI. Still, these measures will not be sufficient to achieve target levels of emission reduction prescribed by IMO. These levels could only be achieved through radical changes in marine power systems, like the transition to alternative fuels with low or zero carbon footprint. This matter will be discussed in the third article of this series.

Object and purpose of research. This paper discusses cavitation erosion on propeller blades. The purpose of this work is to review and analyse modern studies on cavitation erosion, as well as to apply these research results for better under-standing of cavitation damage risk on full-scale propellers. Materials and methods. The paper reviews recent studies on cavitation erosion, as well as the author’s own findings in cavitation erosion on full-scale steel propellers, analyzing the energy needed to create cavitation damage of recorded size. This energy was calculated as per the model based on the results of metallurgical studies discussing the effect of shot blasting upon steel properties. Comparison of these results with those obtained as per classic formulae for the collapse energy of cavita-tion bubble made it possible to estimate the conditions of cavitation erosion on propeller blades. Main results. The review of recent studies on cavitation erosion has shown that current progress in the technologies of experimental studies and computer-based simulations made it possible to considerably improve the knowledge about cavitation erosion process as compared to the level of the 20th century. This review shows that cavitation erosion studies followed three practically independent paths: experimental studies and computer-based simulation of flow around propeller blades with locali-zation of peaks for one or several criteria reflecting the intensity of cavitation energy fluctuations; the studies intended to esti-mate the pressure exerted by collapsing cavitation bubbles and emerging cumulative jets; and finally, the studies on the proper-ties of materials affected by cumulative jets and collapsing bubbles. At this point, it would be practicable to merge these three paths using the results of full-scale cavitation erosion analysis for propellers. KSRC findings in cavitation damage of full-scale steel propeller has shown that cavitation damage recorded in these studies might occur due to a certain combination between the required energy, bubble-blade interaction pressure and the size of affect-ed area on steel blade surface, and this combination, in its turn, might take place when cavitation bubbles consisting of vapour fraction with partial air content hit the blade surface and collapse. Conclusion. This paper shows the capabilities of modern research methods in obtaining new data on the inception mecha-nism of cavitation erosion. Still, to develop the methods for prediction of cavitation erosion (in particular, on propellers), it is necessary to merge the results obtained in different branches of cavitation studies. The basis for this merging could become a power-based analysis of cavitation processes, with help of the cavitation erosion model suggested in this paper and based on the similarity between cavitation erosion and shot-blasting.

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