• Energy Research

Natural gas is cheaper than fuel on an energy basis, making it an alternative ship fuel which leads to a reduced operating cost and clean gas environmental conditions. The current study analyses the retrofit of an ageing multi-purpose ship to use liquefied natural gas as a primary ship fuel in the context of a short-ship sea operation. The objective is to transform an existing commercial ageing ship propulsion system into a green energy propulsion one and to analyse the economic feasibility considering the high volatility and increased LNG price. Four scenarios were analysed based on the net present value representing Denying, Disinterested, Good and Acceptable financial cash outflow. It was concluded that in the present economic instability and price of LNG fuel and CO2 taxes, the ship owner needs to rely on the long-term contract of buying LNG fuel to implement measures to reduce greenhouse gas emissions and keep good benefits in shipping.

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.

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 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.