Ship Operation Research Articles

Contribution of scientists of the Odessa national maritime university to the creation of the theory and methods of management the processing of ship

The article the results of an analytical review of the achievements of scientists of the Odessa National Maritime University – ONMU (formerly the Odessa Institute of Sea Fleet Engineers – OISFE) in the field of creation and development of the theory and methods of management processing of ship (PS) within the limits of intraport operational management (IOM). It is shown that the mentioned scientists were involved in research work in the middle of the 20th century at the stage of formation of IOM as a science. Her first scientific results were the methods of drawing up tape charts, hourly schedules and operational plans for processing of ship. It was noted that in the future, researchers from the OISFE took an active part in providing the methodology of IOM, first of all, the management of PS, the principles, approaches and methodological tools of the sciences born of the scientific and technical revolution, thanks to which it became possible to consider the tasks of PS management in an optimal setting. The methods of solving these problems developed by the scientists of OISFE-ONMU are briefly characterized, starting with the determination of the optimal distribution of port transshipment resources between ships and ending with the search for the optimal option for their use in ship operations are substantiated the main provisions of the system optimization of the PS management as a general direction of the development of IOM at the current stage.

The Development of Ship Recycling Facility Cluster in Indonesia

With a number of 80.849 units ship operating in Indonesia, the Ministry of Transportation estimates that 29,944 units ship of those vessels have been in service for more than 20 years. Furthermore, recycling ships are necessary. Ship Recycling Facility (SRF) should be ecologically friendly following International Maritime Organization (IMO) policy under the Hong Kong International Convention. Docks, cranes, steel cutters, and warehousing are necessary. SRF facilities, along with ecologically suitable hazardous material treatment. If this facility became a cluster, it would operate more effectively. This study aims to provide a different area in Indonesia where a prospective SRF cluster could grow. This research uses Diamond Porter’s method to determine a country’s comparative economic advantage towards the SRF cluster in Alang City, Gujarat, India, which is the global leader in ship recycling. The factor conditions; related and supporting industries; demand conditions; and firm strategy, structure, and rivalry are all examined in this study. To accommodate ship owners, the SRF business, and the government in carrying out ship recycling, the results of this study are a reference for formulating specific regulations for the SRF cluster. This research found that Kamal and Bojonegara are viable for the SRF cluster.

Investigation of Applying Technical Measures for Improving Energy Efficiency Design Index (EEDI) for KCS and KVLCC2

While extensive research is being conducted to reduce greenhouse gases in industrial fields, the International Maritime Organization (IMO) has implemented regulations to actively reduce CO2 emissions from ships, such as energy efficiency design index (EEDI), energy efficiency existing ship index (EEXI), energy efficiency operational indicator (EEOI), and carbon intensity indicator (CII). These regulations play an important role for the design and operation of ships. However, the calculation of the index and indicator might be complex depending on the types and size of the ship. Here, to calculate the EEDI of two target vessels, first, the ships were set as Deadweight (DWT) 50K container and 300K very large crude-oil carrier (VLCC) considering the type and size of those ships along with the engine types and power. Equations and parameters from the marine pollution treaty (MARPOL) Annex VI, IMO marine environment protection committee (MEPC) resolution were used to estimate the EEDI and their changes. Technical measures were subsequently applied to satisfy the IMO regulations, such as reducing speed, energy saving devices (ESD), and onboard CO2 capture system. Process simulation model using Aspen Plus v10 was developed for the onboard CO2 capture system. The obtained results suggested that the fuel change from Marine diesel oil (MDO) to liquefied natural gas (LNG) was the most effective way to reduce EEDI, considering the limited supply of the alternative clean fuels. Decreasing ship speed was the next effective option to meet the regulation until Phase 4. In case of container, the attained EEDI while converting fuel from Diesel oil (DO) to LNG was reduced by 27.35%. With speed reduction, the EEDI was improved by 21.76% of the EEDI based on DO. Pertaining to VLCC, 27.31% and 22.10% improvements were observed, which were comparable to those for the container. However, for both vessels, additional measure is required to meet Phase 5, demanding the reduction of 70%. Therefore, onboard CO2 capture system was designed for both KCS (Korea Research Institute of Ships & Ocean Engineering (KRISO) container ship) and KVLCC2 (KRISO VLCC) to meet the Phase 5 standard in the process simulation. The absorber column was designed with a diameter of 1.2–3.5 m and height of 11.3 m. The stripper column was 0.6–1.5 m in diameter and 8.8–9.6 m in height. The obtained results suggested that a combination of ESD, speed reduction, and fuel change was effective for reducing the EEDI; and onboard CO2 capture system may be required for Phase 5.

Determination of Generator Maintenance Level on Motor Tanker Using Fuzzy Logic

The electricity necessity on the motor tanker are supported by generators with a capacity of 3x1,225 MVA. This generator is used to drive the load of the main engine, pump, cargo plant, and steering system. The problem is how to know the condition of generator performance to be standardized because the generator operation must be available to use to support the ship operation. Consequently, if the generator does not work optimally, the ship operation will be hampered and can be detrimental to the company’s operation. The solution to this problem is the need to carry out appropriate and standardized maintenance. This study focuses on determining the maintenance level for a 3x1,225 MVA ship generator. The model is specified as a scheme of the generator maintenance system. The parameters set include: vibration, insulation resistance, power, and fuel consumption. Fuzzy logic is used to define maintenance actions: corrective, planned, and predictive. The object of this investigation is on MT Salmon Mustafa. The results of this research are that fuzzy logic can be used to determine the level of maintenance actions. The average percentage of the error or uncertainty level measured both by four input variables and by Fuzzy logic consisting of three conditions is 6.9952%. The truth level of the calculation results is 93.0048%. This indicates that the calculation results are sufficiently accurate and reliable.

Energy and speed optimization of inland battery-powered ship with considering the dynamic electricity price and complex navigational environment

Decarbonization has been a trend worldwide, especially in the shipping industry. A pure battery-powered all-electric ship (AES) may be the most flexible way to achieve ship decarburization in recent years. Compared with the conventional ship, the initial investment cost is high, and energy redundancy is low for battery-powered ships. Therefore, an energy management strategy that can minimize the operation cost and guarantee energy use safety is crucial. In this paper, considering the dynamic electricity price and environmental factors, a co-optimization method of ship speed and energy use is proposed for an inland battery-powered ship. Firstly, the energy consumption model is constructed by analyzing the interaction of the hull, propulsion motor, and propeller. Then the speed and energy optimization model is proposed to minimize the ship operation cost. Finally, a neighborhood search differential evolution (NSDE) is adopted to solve the proposed complex nonlinear optimization problem to obtain optimal sailing speed and departure time. Then case study is implemented with an actual battery-powered cargo ship. The results show that the method could provide ship operators a reference for better management of the inland battery-powered AES.

Suggestions on Health and Safety Measures and Epidemic Prevention and Control Measures on Luxury Cruise Ships

In recent decades, there have been a number of large-scale infectious diseases on large cruise ships, which has had a huge negative impact on the development of the cruise industry. A large number of passengers and crew members did not receive timely and adequate medical treatment, resulting in illness aggravation and even death. This paper investigates the weaknesses of luxury cruise in the field of public health and epidemic prevention in the law through the analysis of luxury cruise public health events. In the daily operation of large cruise ships, there are also some health and safety loopholes that are not taken seriously. Some shortages of the epidemic prevention and security risks are found in the field of personnel composition, the health security check during boarding, frequent flow of personnel and medical conditions aboard luxury cruise. There are some suggestions on perfecting the existing legal standard system, improving public health management, speeding up the ventilation system upgrade, improving the ability of medical, etc. The above deficiencies are found and summarized in this paper. It analyzes two cases during the COVID-19 outbreak, and gives suggestions on the prevention and control of the epidemic in the case of outbreaks of infectious diseases on luxury cruise ships. It is hoped that under the cooperation and efforts of various parties, a complete epidemic prevention system and emergency response plan will be established, which will help improve the epidemic prevention and control and response capacity of cruise ships.

Time Charter or Trip Charter? An Assessment of Market Efficiency in Shipping Market

This paper explores the economic value of charter hire rate forecasts in the bulk shipping industry for ship operators by introducing a chartering strategy defined as a sequence of different types of contracts that maximises profit. Ship operators are assumed to divide ship use to trip charter and time charter market depending on the quarterly excess charter hire rate forecasts, i.e. the difference between time charter and trip charter (spot) rates. Ship operators use the recursive forecasting approach and switch the chartering strategy across the two positions. The decision is based on economic measurement rather than statistical significance. The economic benefits realized by ship operators who apply our forecasting rules exceed those derived from the fixed policy approach of using either alternative, and will be used to disprove the validity of the efficient market hypothesis. The paper applies the regression methodology and forecasts two steps ahead of quarterly spot prices regressed recursively on fixed variables, thus extending research in terms of the scope of analysis. We have applied statistical evaluation in addition to the economic evaluation and found that the proposed model outperforms the historical mean forecast. This paper emphasizes the importance of a sound diversification strategy within the business platform to target the more profitable business segment and test if macroeconomic indicators and commodity prices are satisfactory indicators for forecasting charter hire rate.

Simulation Analysis and Experimental Verification of Tribodynamics of Reciprocating Friction Pairs in Low-Speed Marine Engines

The performance of reciprocating friction pairs in low-speed marine diesel engines has an important impact on the economy, stability, and safety of the ship operation, which deserves special attention. However, the available research is very limited. In this article, a new tribodynamics modeling method and an online measurement method for friction force are proposed. The friction force is simulated and verified by experiments. Based on the principle of multibody dynamics and mixed lubrication theory, a tribodynamic model coupling the reciprocating friction pairs (piston assembly–cylinder liner, piston rod–stuffing box, and crosshead slipper–guide) is first established. The friction force and dynamics are theoretically analyzed. Then a friction measurement method, which can measure the friction force of reciprocating friction pairs under engine firing conditions, is developed and used to verify the simulation. By comparison, it is found that the simulated friction is in good agreement with the experimental one. The results show that the crosshead slipper and piston assembly have obvious secondary motion, which will affect the vibration and noise of the engine. The friction force of the piston assembly is much higher than that of other reciprocating friction pairs. Improving the lubrication state near the top dead center of the piston assembly is of great significance to reduce the friction loss of the low-speed marine engines.

Identifying essential skills and competencies towards building a training framework for future operators of autonomous ships: a qualitative study

AbstractPast and ongoing research in the design, development, and implementation of fully autonomous and unmanned ships has revealed operational, environmental, and financial benefits for the maritime industry. However, with the benefits of being highly intuitive and intelligent systems, there are risks of mistakes and failures caused by their operators i.e. the unavoidable human element. With predictions of both seafarers and non-seafarers to be involved in the critical operations of autonomous vessels, it was imperative to identify key maritime stakeholders and conduct research which would investigate their beliefs and perceptions on the training requirements of the future shore-based operators. The key maritime stakeholders were 37 participants who were a mix of seafarers, maritime regulators, maritime education and training providers, and persons involved in other facets of the maritime business. The qualitative research involving in-depth interviews with the participants provided key insights which helped in identifying essential skills and competencies towards building a recommendatory framework which can be used as a basis to reform the Standards of Training, Certification, and Watchkeeping (STCW) Code in order to make seafarers future ready.

Insight into the marine microplastic abundance and distribution in ship cooling systems

Microplastics (MPs) are becoming widely recognized as one of many global environmental issues. Although recently, it has been suggested that marine plastics may affect a ship's operation, the presence of MPs in a ship's cooling system has not received significant attention. In this study, samples of 40 L each were taken from each of the five main pipes (sea chest (SC), ejector pump (EP), main engine jacket freshwater pump (MJFP), main engine jacket freshwater cooler (MJFC), and expansion tank (ET)) in each season (February, May, July, October 2021) to identify and characterize MPs in the five main pipes of the ship cooling system from the training ship Hanbada, Korea Maritime and Ocean University. As a result of FTIR analysis, the total MP abundance was 24,100 particles/m3 in the cooling system of the ship. MP concentrations were observed to be higher (p < 0.05) in winter and spring (dry season: 1578 ± 604 particles/m3) than in summer and autumn (wet season: 990 ± 390 particles/m3). In addition, the MP concentration in the seawater cooling system (SCS) (1509 ± 553 particle/m3) was slightly higher (p > 0.05) than that in the freshwater cooling system (FCS) (1093 ± 546 particles/m3). Compared to previous studies, it was confirmed that the quantitative amount of MPs on board was similar to or slightly less than the concentration of MPs investigated along the coast of Korea (1736 particles/m3). To identify the chemical composition of MPs, an optical microscope and FTIR analysis was carried out, and PE (polyethylene), PP (polypropylene), and PET (polyethylene terephthalate) were identified as major chemicals in all samples. MPs in the form of fibers and fragments accounted for approximately 95% of the total. This study provided evidence of MP contamination in the main pipe in the cooling system of the ship. These findings confirm that marine MPs existing in seawater may have flowed into the ship's cooling system, and it is necessary to understand the effect of marine MPs on the ship's engine and cooling system through continuous monitoring.

A Novel Underwater Acoustic Target Identification Method Based on Spectral Characteristic Extraction via Modified Adaptive Chirp Mode Decomposition

As is well-known, ship-radiated noise (SN) signals, which contain a large number of ship operating characteristics and condition information, are widely used in ship recognition and classification. However, it is still a great challenge to extract weak operating characteristics from SN signals because of heavy noise and non-stationarity. Therefore, a new mono-component extraction method is proposed in this paper for taxonomic purposes. First, the non-local means algorithm (NLmeans) is proposed to denoise SN signals without destroying its time-frequency structure. Second, adaptive chirp mode decomposition (ACMD) is modified and applied on denoised signals to adaptively extract mono-component modes. Finally, sub-signals are selected based on spectral kurtosis (SK) and then analyzed for ship recognition and classification. A simulation experiment and two application cases are used to verify the effectiveness of the proposed method and the results show its outstanding performance.

Improving shore power project economics at the Port of Aberdeen

Shore power is one of just a few technologies available to the shipping sector that has potential to deliver carbon reductions this decade in line with the Paris Climate Agreement. Shore power connects ships to land-side electricity grids, reducing fossil fuel use while at berth in port and at the same time improving air quality. It is also an enabling technology for the future deployment of electric vessels, allowing battery recharge. Despite being a proven technology, global deployment has been slow, with the literature pointing to clear economic barriers to its uptake. These include high capital costs for ports, high taxes on land-side electricity and the global lack of taxation on ships’ fuel oils. Yet there is a gap in understanding around how to overcome these barriers. Here, a case-study of the Port of Aberdeen in Scotland is used to explore how the economic case for a shore-power system can be improved. A multi-criteria analysis and techno-economic assessment, coupled with port-user and supplier engagement, applicable to other port contexts, sheds light on how to create the much-needed acceleration of shore-power deployment. By building a collaborative approach between the port, ship operators and national government, project viability can be unlocked to more closely align the sector’s future carbon pathway with the high ambitions laid out in Paris 2015.

The concept phase design of LNG tank and the fuel supply system on dual-fuel ships

ABSTRACT To reduce pollution, LNG is increasingly used as a fuel in the maritime industry. This paper provides a methodology for the concept phase design of the LNG tank and fuel supply system on a ship. First, constraints of the ship, fuel tank and supply are determined. Next, the simultaneous design and optimisation of the fuel tank and supply system under defined constraints and realistic operating profiles is done. Tank design includes tank type, dimensions, insulation and design pressure analysis and structural strength assessment. Fuel supply system analysis is conducted using the developed dynamic model for comparing system configurations and equipment sizing. The methodology is demonstrated on two dual-fuel cruise ships of different sizes. The influence of ship operating conditions on the tank and fuel supply system and their interdependence is examined. Several candidates for the optimal tank design and fuel supply system are determined based on conflicting design objectives.

An integrated risk assessment modelling for cargo manifold process on tanker ships under FMECA extended Dempster–Shafer theory and rule-based Bayesian network approach

Risk assessment is one of the top requirements in maritime transportation due to the complexity of ship operations, particularly on tanker vessels. By carrying hazardous liquid cargo, tankers pose significant risks for life, property and the marine environment, which should be assessed in detail. This paper focuses on the manifold process during tanker cargo operation since it involves various risks that may lead to severe consequences such as human injury, gas poisoning, hull damage, cargo spill or explosion. The process is modelled via Bayesian network, and marine experts evaluate 12 failure modes with respect to Failure Mode, Effect and Criticality Analysis parameters. To fuse the expert judgment, Dempster–Shafer theory is applied with a rule-based approach in the Bayesian model. The highest crisp risk value is found 48.85 for Failure Mode (FM) 1.1 (Improper arrangement of valves and pipelines to be connected). It is followed by FM 1.2 (Improper connection between the line and the manifold) with a crisp risk value of 45.83, and FM 4.1 (Failure in earthing & bonding condition of equipment to be used) with 38.26 crisp risk value. According to results, control actions are presented to reduce the risks during the manifold process. Beside its technical background, the paper provides utmost contributions to maritime safety inspectors, tanker ship crew, tanker ship operators and safety researchers to improve safety process and minimize the operational risks of cargo manifold process.

Research on Price Evaluation of Second-hand Container Ship based on GA-BP Neural Network

As a capital investment, whether the investment in second-hand container ships can bring benefits to the enterprise depends on whether the benefits of ship operation can repay the investment and obtain certain profits. The purchase price of second-hand ships is the key factor, so an evaluation model is built to predict the price of second-hand container ships and evaluate its rationality. To help enterprises better understand the actual price of ships when buying and selling ships, and hope to improve the market evaluation system. In order to accurately evaluate the price of second-hand ships, the Clarkson database was used to obtain 362 container ship transaction data from December 2019 to December 2022, and a GA-BP network neural model based on ship age, deadweight tonnage and new shipbuilding price was established. The weights and thresholds were optimized through genetic algorithms, and then assigned to the BP neural model. The test results show that the mean square error is 0.0185, the evaluation error is basically 20%, and the error within 10% accounts for nearly half. It is proved that the model can preliminarily evaluate the transaction price of second-hand ships, and has certain feasibility and rationality.

Energy, environmental and economic investigations of cruise ships powered by alternative fuels

In recent years, methanol, ammonia and methane–hydrogen blends are currently receiving most of interest as green fuels enabling energy transition in the maritime sector. In this work, the energy, environmental and economic performances offered by these alternative fuels applied to modern large-size cruise ships are investigated. Overall, 5 different routes, three different operating conditions (maneuvering, port and navigation) and summer–winter seasons have been accounted for. Due to the enhanced fuel flexibility of gas turbines, attention is here focused on power configurations integrating combined gas electric and steam plants with reciprocating engines. First, a cogeneration efficiency optimization study has been carried out considering variable ship operating conditions. Interestingly, combined gas steam power plants resulted to cover up to 68% of the overall thermal power request and to provide energy savings when electrical power demand exceeds 15 MW during navigation and maneuvering. Methane–hydrogen blends enabled the highest cogeneration efficiencies (i.e. ≈82%). Successively, environmental impact of power plants is assessed by means of the Energy Efficiency Design Index and Carbon Intensity Indicator, whose attained values have been shown to comply with regulation limits up to 2025 and 2050, respectively, under ammonia and methane–hydrogen feeding conditions. On the contrary, methanol appears a valuable option only for a short-term energy transition perspective, since compliance with regulations lapses before 2028. Finally, investments and operational costs for power plants have been computed to assess their economic viability. In the current scenario, comparable costs result for ammonia and methanol fueled cruise ships, while 40–60 M€increase in operational expenditure is achieved at 25-th year by methane–hydrogen blends due to the high price still affecting green hydrogen.

A smart predict-then-optimize method for targeted and cost-effective maritime transportation

In maritime transportation, port state control (PSC) is the last line of defense against substandard ships. During a PSC inspection, PSC officers (PSCOs) identify ship deficiencies that lead to a ship's detention, which can cause severe economic and reputational losses to the ship operator. Therefore, this study innovatively uses PSC inspection data to design ship maintenance plans for ship operators to minimize overall operational costs. We identify three types of operational costs associated with each deficiency code: inspection cost, repair cost, and risk cost in the ship operators’ decision-making process. The risk cost of a deficiency code is strongly related to the detention contribution of the deficiency items under a deficiency code, as indicated by the feature importance of that code in the random forest (RF) model used to predict detention outcomes. To design ship maintenance plans, the sequential predict-then-optimize (PO) method typically solves the optimization problem using input parameters, including the predicted probabilities of having deficiency items under each code and the three types of operational costs. However, the loss function in this two-stage framework does not consider the effect of predictions on the downstream decisions. Hence, we use a smart predict-then-optimize (SPO) method using an ensemble of SPO trees (SPOTs). Each SPOT uses an SPO loss function that measures the sub-optimality of the decisions derived from the predicted parameters. By exploiting the structural properties of the optimization problem analyzed in this study, we demonstrate that training an SPOT for this problem can be simplified tremendously by using the relative class frequency of true labels within a leaf node to yield a minimum SPO loss. Computational experiments show that the SPO-based ship maintenance scheme is superior to other schemes and can reduce a ship's total operating expenses by approximately 1% over the PO-based scheme and by at least 3% over schemes that do not use machine learning methods. In the long run, SPO-based ship maintenance plans also improve the efficiency of port logistics by reducing the resources needed for formal PSC inspections and alleviating port congestion.

Completeness Of Documents On Speedboat Seaworthiness At Pier 16 Ilir Palembang City, South Sumatra Province

In Palembang City, there are several Port Service Units, one of which is the 16 Ilir Pier Service Unit. At Pier 16 Ilir there are still many speedboats that do not complete the Ship's Seaworthiness Documents such as Ship Measurement Letters, Registration Letters (Gross Deeds), Ship Nationality Certificates (River and Lake Passes), River and Lake Ship Safety Certificates (SKKSD), and Crew Skills Certificate. This research is a type of qualitative research method, qualitative research emphasizes quality not quantity and the data collected does not come from questionnaires but comes from interviews, direct observations and related official documents. The data used are primary and secondary data to be analyzed. Based on the results of an interview survey conducted at Pier 16 Ilir Palembang City, 100% Speedboats that have not completed the ship's seaworthiness documents. The reason for the operator or ship owner has not completed the ship's seaworthiness document, namely 42% do not meet the requirements for making shipworthiness documents, 37% lack of checking ship documents, 21% do not know the procedure for making ship seaworthiness documents. Therefore, to overcome these problems, it is necessary to conduct socialization regarding the completeness of the ship's seaworthiness documents as well as the requirements in making the ship's seaworthiness documents to the ship's owner or operator and it is necessary to coordinate with the relevant agencies in the fulfillment and affirmation of the applicable rules regarding the completeness of the ship's seaworthiness documents with conduct socialization and ease of registration regarding the importance of completeness of ship's seaworthiness documents.

Influence of Key Process Parameters on Vibration Characteristics of Centrifugal Pump

The low-noise operation of ships will be affected by the vibration of centrifugal pumps, which are widely implemented in vessels. Available papers mainly focused on the structural optimization of pump components with less concentration on their assembly process, which include coaxiality, circle-runout and clearance fit, etc. The clearance between the impeller and wear ring, which is named wear-ring clearance, is influenced by the manufacturing and assembly process and has an impact on vibration. An investigation of the influence of key process parameters on the vibration characteristics of the pump based on wear-ring clearance is presented. A numerical model of the internal flow field of the pump is presented. The dynamic behavior in the frequency domain is obtained for fluid-solid interaction. The vibration is found to be more pronounced at some frequencies. A closed-loop dimensional chain system is constructed targeting the wear-ring clearance, and the circle-runout and coaxiality of some parts are found to have a prominent influence on it. A relationship between the key process parameters of the pump and vibration characteristics is established.

Research on the Improvement of Safety Navigation Based on the Shipmaster’s Control of Ship Navigational Parameters When Sailing in Different Sea State Conditions

Shipmasters must make several quick decisions with respect to the ship’s speed and heading when new sea conditions approach. The implications for ship stability and risky situations are known but there are no guides on how they should be addressed in this limited period of time. In the present paper, and from three points of view, the ship’s rolling motion in the long-term domain is analysed. Firstly, the ship’s behaviour after the influence of a single and external force was studied. Secondly, the influence of successive regular beam seas, with resistance and at zero-speed conditions, was analysed. Finally, the influence of wave direction on a ship sailing at non-zero speed was investigated. Results showed that once five minutes elapse, the rolling angle tends to be null regardless of the ship’s loading condition and that after a certain period of time, a coupling of the ship’s rolling frequency with the waves’ period and angle amplitude occurs. This circumstance was noted after three minutes for all of the ship loading conditions. Finally, novel guides for shipmasters in the form of 3D maps and polar diagrams were proposed to improve the ship’s behaviour-altering navigational parameters (heading and ship’s speed) when sailing in changing weather conditions. Therefore, for the three approaches, the relevant results and novel mathematical relations of linear factors were obtained which can be considered useful and applicable by the ship operators of most fishing and merchant fleets (regardless of their sizes) when they are operating under normal loading conditions.