Friction-induced wear during the rolling process needs periodic remachining of caliber roll grooves, which increases operational costs and reduces roll fatigue life. Stress analysis showed that a regular reduction in the initial diameter by up to 3.5% results in a 12.2% increase in maximum stress amplitude, reducing the estimated fatigue life by a factor of 1.5. Although fatigue life is reduced, the risk of failure under normal operating conditions remains low. Further analysis, considering mill design and roll hardness, demonstrated the feasibility of additional roll diameter reduction, thereby enabling increased production using the same rolls. The findings support further diameter reduction without compromising performance and underscore the importance of integrating such analysis into the roller design process to optimize fatigue life and roll utilization.

Computerized maintenance management systems (CMMSs) are software packages that support or organize the maintenance tasks of assets or equipment. They are found in the background of any ship maintenance operation and are an important part of maintenance planning, spare parts supply, record keeping, etc. In the marine market, there are a number of CMMSs that are competing fiercely to program a better and more modern program that will capture the market, which has been accompanied by published analyses and scientific papers. At the same time, the quality of the data entered into CMMS databases is questionable, a fact that has been ignored in practice and scientific circles; until recently, there were no published analyses and there was no way to measure the quality of the data entered. This article presents two proposals for improving the quality of CMMS databases and calculates their potential benefits. By implementing the first proposal, the evaluation methodology for the ship’s Planned Maintenance System database, between 10% and 15% of databases will have significant financial or safety benefits. This measure will also have an impact on more than 40% of the other databases that can also be improved. The second proposal will have a smaller impact of only 4%. The overall benefit of these proposals is to improve more than 60% of the databases and will result in a significant increase in safety or financial savings.

Calculation of torsional vibrations is essential in the early phase of the design of any ship propulsion system, after selection of shafting diameters in accordance with the Classification Rules. Later on, during ship trials, the calculation shall be validated by measurements on board. The calculation results depend upon inertial moments of actual masses, stiffness of shafting components, damping in the actual shafting components, as well as the excitation forces and moments exerted by the propulsion engine(s) and the propeller. Inertial moments and stiffness can be determined with no ambiguities. However, this is not the case with either the damping, or the engine excitation. Actually, during validation on board the calculation supposed damping is the main influential factor to be verified. The aim of this paper is to present and compare several models to define and compare damping definitions in the the torsional vibrations calculation (Frahm's model, Archer's model, physical damping, magnification factor, etc.) in a systematic way, to enable designers to correctly apply the selected damping model. Further on the engine excitation may be expressed by means of cylinder pressures or tangential forces to the cranks. The essentials of the two models and the procedure to convert one excitation model into another one are also presented. The application of the presented damping and excitation models is presented on an actual ship propulsion system and conclusions drawn.

Split Trailing Suction Hopper Dredgers (TSHD) are special type of working ships, whose hulls open to discharge cargo to certain unloading positions while being at sea. Although they have variable hull geometry, their hydrostatic and stability characteristics are usually calculated for unchanged initial hull geometry loading conditions only, and such calculations are supported by classification society stability regulations for that ship type. Nevertheless, in this study, we show that hydrostatic particulars for intermediate loading conditions of variable ship geometry can be calculated by using analytical solutions of basic hydrostatic integrals for arbitrary list angles, obtained for polynomial radial basis function description of ship geometry. The calculations will be performed for symmetric hopper opening during cargo discharge procedure, thus covering all Split TSHD regular unloading conditions, without examination of ship hull opening failure modes. Thus, all ship hydrostatic properties will be pre-calculated analytically and prepared for further stability calculations, as opposed to the usual numerical calculations for initial geometry and even keel only, as currently used in naval architecture design.

This paper examines the problem of evaporation of Liquefied Natural Gas (LNG) occurring at different places in the LNG supply chain. Evaporation losses in the LNG supply chain are one of the key factors for LNG safety, technical and economic assessment. LNG is stored and transported in tanks as a cryogenic liquid, i.e. as a liquid at a temperature below its boiling point at near atmospheric pressure. Due to heat entering the cryogenic tank during storage and transportation, a part of the LNG in the tank continuously evaporates creating a gas called Boil-Off Gas (BOG), which changes the quality of LNG over time. The general methods of handling and utilization of the Boil-Off Gas at different points in the LNG supply chain are presented. Attention is given to the issue of LNG energy content transferred during loading and unloading of LNG tankers, as well as to the Boil-Off Gas generated by evaporation of the cargo during maritime transport. The results presented in the paper have been derived from the scientific research project 250 - 2502209 - 2366, "Management of Ship Power Systems under Fault Conditions and Failure" supported by the Ministry of Science, Education and Sports of the Republic of Croatia.

Owing to ever increasing share of the natural gas in the world consumption of the power sources, the international maritime traffic with the liquefied gas is recording constant growth with even greater future anticipations. It results in the need for the construction of new LNG receiving terminals. In order to be integrated in those trends and to make provisions for additional quantities of power sources necessary for its future economic development, the Republic of Croatia is making plans for the construction of such a terminal. Successful planning and designing of LNG terminal depends on the application of appropriate methodology for the evaluation of terminal capacity. This paper gives a simulation method for the evaluation of receiving LNG terminal capacity. KEY WORDS: liquefied natural gas, receiving terminal, evaluation of terminal capacity, model, discrete simulation.

Increasing the energy efficiency of the marine propulsion systems currently represents one of the priorities that have been placed in front of all subjects of maritime shipping market. More and more ship owners aspired to larger and more powerful diesel engines demanded from the marine engine manufacturers to implement various technological modifications to increase the engine efficiency, extend the life of engine components, and thus prolonge regular overhauling period of them. One of the way to meet these demands, among other things, is to improve the tribological characteristics of engine components. The aim of this paper is to present structural modification of tribological system "cylinder liner - piston ring - piston" of large bore slow speed marine diesel engine to reduce friction problems in mentioned system

Marine diesel engine is a complex multivariable nonlinear dynamic system. Its basic structure consists of interdependent and connected subsystems with a large number of different components. Faults can appear in any component of the system. Therefore, for improving reliability and marine engine systems safety fault diagnosis methods are more and more important. This paper gives an especial review on interference diagnosis methods in a function of timely localization and isolation of faults. Fault tree analysis shows all causes of heavy fuel oil separator incorrect operation. Influence of impurities in fuel oil on environment and possible fuel oil system faults as a direct consequence of separator incorrect operation has been analyzed. Fuel oil systems faults have been simulated using Full Mission Engine Room simulator Kongsberg Norcontrol. Symptom behavior in time has been presented by binary matrix. Table analysis has been conducted by fuzzy facts. Results obtained through simulation point to the importance of fault diagnosis for the timely prevention of the occurrence of faults, thereby contributing to the reliability and availability of marine engine systems.

Brodski dizelski motor je složen multivarijabilni nelinearni dinamički sustav. Njegova osnovna struktura se sastoji od međusobno povezanih podsustava i velikog broja različitih komponenti, te se kvarovi mogu pojaviti na bilo kojoj komponenti sustava. Stoga, za poboljšanje pouzdanosti i sigurnosti brodskih strojnih sustava metode dijagnostike kvarova imaju sve veću i veću važnost. Ovaj rad pruža poseban osvrt na dijagnostičke metode zaključivanja u funkciji pravovremene lokalizacije i izolacije kvarova. Analiza stabla kvarova prikazuje sve uzroke neispravnog rada separatora teškog goriva. Analiziran je utjecaj nečistoća u gorivu na okoliš i moguće kvarove u sustavu goriva kao izravna posljedica neispravnog rada separatora. Kvarovi u sustavu goriva su izvedeni na brodostrojarskom simulatoru Kongsberg Norcontrol. Ponašanje simptoma u vremenu prikazano je binarnom matricom. Analiza tablice izvedena je uz pomoć neizrazitih činjenica. Rezultati dobiveni simulacijom ukazuju na važnost dijagnostike kvarova u svrhu pravovremenog sprječavanja pojave kvarova, čime se doprinosi pouzdanosti i raspoloživosti brodskih strojnih sustava.

Enviromental protection and preservation of human environment have recently become one of the most important parts of scientific advanced research. Since they primarily resolve the issues of pollution from shore, today the attention has been focused to the pollution from ships. Air pollution is a serious problem for both human health and the overall ecosystem. Emissions from ships include air pollutants, greenhouse gases and substances that destroy the ozone layer with the consequence of endangering human health and the environment. Emissions of sulfur (SOx) and nitrogen oxides (NOx), which causes acidification adversely affects the environment and human health. Emissions of volatile organic compounds (VOCs) from tankers, combined with nitrous oxide, participate in the formation of ground-level ozone, which adversely affects the health and the environment. Air pollution knows no borders and it is one of those areas that require the highest level of international cooperation. The reason for the intense need for a solution to this problem is the growing increase in air pollution emissions form ships because the emissions of stationary plants significantly reduced the adoption of various environmental laws. This problem has priority, so the international and national regulations on emission limits from ships in some countries, have been adopted especially those which are exposed to more emissions from ships, which are closer to the sea waterway.

The results of experimental determination of the actual flow rate external gear pump show that increasing pressure reduces the value of the actual flow rate and volumetric efficiency of the pump. On the basic of hydrodynamic characteristics of the pump, mathematical expressions for the actual flow rate and volumetric efficiency have been given. The applied measuring system is described and measurement results have been presented. In accordance with Poiseuille's law, assuming that the physical properties of liquid are constant, a little pressure on the suction side of the pump is ignored. By the method of approximation of measurement results using linear regression defined model of the actual flow rate of the pump.On the basis of a defined experimental model for different values of pressure of the pump, values of volumetric efficiency of the pump have been calculated which differ less than 1% of the experimentally determined values, what justifies the model application. The resulting model allows the determination of the actual flow rate of the pump and volumetric efficiency as a function of pressure at the pressure side of the pump.