Petar Georgiev

Articulated Tug-Barge systems connect a tugboat and a barge via an articulated link, improving manoeuvrability and flow, and offering opportunities for greater efficiency. Due to their size, these systems are vital to waterborne cargo distribution, managing the transport of several types of oil, chemicals, and bulk goods, as well as container barges. The interest in these systems is driven by the rising demand for energy efficiency and environmentally friendly maritime transport. Analysing reliability, costs, environmental and operational conditions, and crew experience helps manage each design option more effectively. The dual-mode Articulated Tug-Barge (ATB) system can disconnect the tug from the barge when seaway loads reach design limits. Effective load management and real-time monitoring are essential in these situations. This research introduces a method for evaluating barge efficiency using a structural reliability index and associated costs, accounting for environmental conditions, operational scenarios, and crew experience. The reliability index assesses the barge’s hull integrity, accounting for environmental pollution from oil spills and air emissions from construction and operation, as well as crew proficiency. The chosen design, operational status, crew experience, hull failure progression, and their effects on structural integrity, along with impacts on the ship, cargo, and environment from construction, voyages, and cleaning, are all incorporated into the cost analysis. Mitigating risk measures focus on improving the crew experience, directly reducing costs and enhancing reliability without requiring additional structural materials to increase strength.

Starting January 1, 2025, shipping companies will be required to monitor and record greenhouse gas (GHG) emissions data for each ship arriving at or departing from a port in the European Union. This requirement is part of the FuelEU Maritime regulation and applies to all vessels with over 5,000 gross tons for transporting passengers or cargo for commercial purposes. The FuelEU regulation includes a calculation scheme and sets limits on GHG intensity, aiming for an 80% reduction in emissions compared to 2020 levels by 2050. Short-sea shipping plays a crucial role in the European Union’s transportation policy. The study’s objective is to analyse the GHG emissions of the containerships registered from 2020 to 2023 vessels, utilising EU-MRV data from 2020 to 2023. Applying the extreme values analysis indicates no consistent trend toward reducing GHG intensity, illustrating the complexities in mitigating the GHG intensity levels requiring additional measures to achieve the proposed reduction by 2050.

Articulated Tugs and Barges (ATBs) are increasingly recognised for their effectiveness in transporting chemicals, petroleum, bulk goods, and containers, primarily due to their exceptional flexibility and fuel efficiency. Recent projections indicate that the ATB market is on track for significant growth, which is expected to lead to an increase in the annual growth rate from 2025 to 2032. This study aims to analyse the current advancements in ATB technology and provide insights into the ATB fleet and the systems that connect tugboats and barges. Furthermore, it highlights the advantages of this transportation system, especially regarding its role in enhancing energy efficiency within the maritime transport sector. Currently, there is limited information available in the public domain about ATBs compared to other commercial vessels. The analysis reveals that much of the required information for modern ATB design is not accessible outside specialised design companies. The study also focuses on conceptual design aspects, which include the main dimensions, articulated connections, propulsion systems, and machinery, concluding with an evaluation of economic viability. Special emphasis is placed on defining the main dimensions, which is a critical part of the complex design process. In this context, the ratios of length to beam (L/B), beam to draft (B/D), beam to depth (B/T), draft to depth (T/D), and power to the number of tugs cubed (Pw/N³) are established as design control parameters in the conceptual design phase. This aspect underscores the novelty of the present study. Additionally, the economic viability is analysed in terms of both CAPEX (capital expenditures) and OPEX (operational expenditures). While CAPEX does not significantly differ between the methods used in different types of commercial ships, OPEX should account for the unique characteristics of ATB vessels.

This review looks at the advancements in shipping-related air pollution prevention in the context of ship life cycle assessment and energy efficiency. It discusses which design option is best for implementing various strategies to lower greenhouse gas emissions. It covers logistics, digitization, environmental requirements, and the greenhouse gases produced. Among the issues for enhancing the propulsion system’s performance are air lubrication, ship hull optimization, and hull and propeller maintenance and cleaning. Alternative fuels, wind-assisted propulsion, and nuclear energy are given special attention. Energy-efficient design solutions, risk-based environmental ship design, and retrofitting older ships to improve energy efficiency are also covered. Several trends and recommendations for lowering shipping-related air pollution have been found in the review.

The study’s objective is to create a method to select the best course of maintenance action for each state of ship propulsion system degradation while considering both the present and future costs and associated carbon intensity indicator, CII, rates. The method considers the effects of wind and wave action when considering fouling and ageing. The ship resistance in calm, wave, and wind conditions has been defined using standard operating models, which have also been used to estimate the required engine power, service speed, fuel consumption, generated CO₂, CII, and subsequent maintenance costs. The maintenance takes into consideration the effects of profit loss because of lost opportunities and efficiency over time. Any maintenance choice has total costs associated with it, including extra fuel, upkeep, and missed opportunities. Using a discrete-time Markov chain, the ship’s propulsion system maintenance schedule is optimized. A decision has been reached regarding the specific maintenance measures to be undertaken for each state of the Markov chain among various alternatives. The choice of optimal maintenance is related to a Markov decision process and is made by considering both the current and future costs. The developed method can forecast the propulsion system’s future states and any required maintenance activities.

A formulation is presented for the assessment of the CO₂ generated by ships in operation and their evolution with time, conditional on the current legislation using Markov chains. Any potential deep repair or retrofitting of the ship propulsion system or enhancement of route operational characteristics during the service life are not accounted for. The Markov transition matrix is defined based on the ship operations and CO₂ history of A, B, C, D, and E carbon intensity indicator (CII) rates. The transition between different CII rate states in the survey data is used to estimate the probability of transition of the analysed ships between different CII grates. Distinct transition matrices employing the progressively tightened legislation of CII are employed and analysed. In addition, the transition matrices can be fed into risk-based models that take the CII rates as input for defining the most appropriate ship energy efficiency management plan.

This work analyses the operational characteristics, including the fuel consumption and carbon emissions of self-reported data of container vessels performing regular short sea voyages in the Black Sea. The data are extracted from the EMSA THETIS-MRV database covering the period of 2018–2021. The main particulars of container ships that visited six Black Sea ports were collected from the Marine Traffic platform and Equasis database. Several conclusions about the status of carbon emissions from container shipping in the Black Sea are presented, which may support the short shipping companies in developing measures to incentivise decarbonisation in the region. It has been identified that the correlation between ship deadweight and total fuel consumption and CO₂ emissions is weaker than the correlation between distance travelled and transport work. The decrease in CO₂ emissions in 2021 can be attributed to reduced ship activity and emission-reduction measures. The ratios of CO₂-related indicators to ship deadweight are more diminutive, showing a lack of correlation. An approach based on the confidence ellipses is employed in performing an innovative analysis of the CO₂ emissions over the years for container ships operating in the Black Sea. This is important due to the new requests for using EEXI and CII.

This work uses the environmental contour line approach to estimate the long-term extremes of carbon emission generated by a bulk carrier operating in different sea state conditions, utilising short-term analyses of the ship propulsion energy efficiency as a function of hull resistance in calm water due to appendages, aerodynamic resistance, and added wave resistance, resulting in the required permanent delivered power and the one induced by the waves. The analysis accounts for the ship’s main characteristics, operational profile based on mission conditions, and wave climatic data. All sources of inherent uncertainties are accounted for through the variability in the 3 h extreme value in any sea state in the long term, and the inverse first-order reliability method (IFORM) is employed in predicting the extreme operational carbon intensity indicator (CII). This study develops proper wave scatter diagrams as a function of the route description. The CII measures the energy efficiency of the installed propulsion system, accounting for the ship’s operational characteristics, such as the annual fuel consumption with corresponding CO₂ factors, annual distance travelled, and capacity. The present study is limited to one operation route but can be extended to any other possible voyage or sea area. The estimated CII defined from the complete probabilistic characterisation of the sea state conditions conditional to the short-term maximum response is a rational approach that can be used for optimising the ship’s main characteristics, propulsion system, operational profile, and chosen route to achieve the best ship performance and energy efficiency.