IVL Swedish Environmental Research Institute

Electrification of ships offers zero-emission travel and is spreading rapidly, but the relation between electric ship propulsion and noise pollution is not generally understood. Here, three different types of diesel-electric hybrid ferries have been measured in two operating modes: running in hybrid mode with the diesel engine powering an electric generator; and running in fully electric battery powered mode. Measurements were performed to simultaneously quantify airborne and underwater radiated noise. Findings are that on-board diesel engines for electricity generation do not contribute a large extent of the underwater radiated noise, whilst a major source of airborne low-frequency radiation.

Electrification of ships offers zero-emission travel and is spreading rapidly, but the relation between electric ship propulsion and noise pollution is not generally understood. Here, three different types of diesel-electric hybrid ferries have been measured in two operating modes: running in hybrid mode with the diesel engine powering an electric generator; and running in fully electric battery powered mode. Measurements were performed to simultaneously quantify airborne and underwater radiated noise. Findings are that on-board diesel engines for electricity generation do not contribute a large extent of the underwater radiated noise, whilst a major source of airborne low-frequency radiation.

Emissions of exhaust gases and particulate matter from a dual fuel marine engine using methanol as fuel with marine gasoil as pilot fuel have been examined for a ferry during operation.

The emission factor for nitrogen oxides is lower than what is typically found for marine gasoil but does not reach the tier III limit. The emissions of particulate matter are significantly lower than for fuel oils and similar to what is found for LNG engines.

The main part of the particles can be found in the ultrafine range with the peak being at around 18 nm. About 93% of the particles are evaporated and absorbed when using a thermodenuder, and thus a large majority of the particles are volatile. Methanol is a potential future marine fuel that will reduce emissions of air pollutants and can be made as a biofuel to meet emission targets for greenhouse gases.

Underwater noise and its negative impact on marine life is a growing environmental concern where scientific knowledge is increasing but mitigation is scarce. This report is the outcome of a joint effort of the IVL Swedish Environmental Research Institute and the Swedish Maritime Administration that addresses this challenge.

Motivated by environmental concerns and coming EU legislation, our vision is that Sweden should become the first country to implement national incentives for underwater noise mitigation. The technical aspects of ship underwater noise are relatively well known.

At cruise speed, cavitation at the propeller is typically the dominant source of underwater noise, but this is not true for all ships. Standardised measurement methods exist but are costly to implement. Prediction models are useful for noise mapping and fleet-wide estimates but not sufficiently accurate for individual ships. 

The environmental impact of underwater noise from shipping has gained increased scientific attention in recent years. While many studies have been made, dose-response relationships and thresholds for different effects are largely unknown. Behavioural effects, including escape reactions, difficulty to avoid predators and masking of important communication calls, have been observed across a large number of species upon exposure to ship noise.

There are no national or international binding rules on ship underwater noise emissions. The International Maritime Organisation is currently updating its voluntary guidelines on ship underwater noise. The EU is introducing legislation on permissible levels of ship underwater noise in the environment, which is expected to come into force in member states within a few years.

Technical methods for mitigation of underwater noise are known but not independently validated. Ship speed reductions may reduce underwater noise but may incur increased operational costs at the ship owners. Stakeholders in ship underwater noise mitigation are found across ship owners, the ship design and technology industry, research bodies and authorities.

Through interviews and workshops a network of relevant stakeholders in Sweden has been established. A stakeholder analysis showed that there is a need for more knowledge on ship underwater noise and its environmental impacts as well as its mitigation. Fairway design for reduced transmission of underwater noise to the environment was investigated by long-term measurements at different sections of the fairway leading to Västerås in lake Mälaren. Neither depth nor a turn could be demonstrated to have an effect on the radiated noise.

A more detailed experiment would be required to clarify if fairway design is a viable alternative for noise mitigation. Six different ways of designing a financial incentive for ship underwater noise reduction were described. Rewarding speed reductions or technical measures for noise mitigation is feasible but the scientific basis is not clear. An incentive may be based on a silent ship notation from a classification society, but these are not commonly issued.

A noise inquiry may be performed, but it may be difficult to identify the most relevant mitigations without underwater noise measurement. Bespoke measurement stations at or near port inlets may be a cost-effective way to collect measurement data, but the accuracy of such opportunistic measurements would need to be improved if the data is to be used for a financial incentive.

In response to stricter regulations on ship air emissions, many shipowners have installed exhaust gas cleaning systems, known as scrubbers, allowing for use of cheap residual heavy fuel oil. Scrubbers produce large volumes of acidic and polluted water that is discharged to the sea. Due to environmental concerns, the use of scrubbers is being discussed within the International Maritime Organization. Real-world simulations of global scrubber-vessel activity, applying actual fuel costs and expenses related to scrubber operations, show that 51% of the global scrubber-fitted fleet reached economic break even by the end of 2022, with a surplus of €4.7 billion in 2019 euros. Within five years after installation, more than 95% of the ships with the most common scrubber systems reach break even. However, the marine ecotoxicity damage cost, from scrubber water discharge in the Baltic Sea Area 2014–2022, amounts to >€680 million in 2019 euros, showing that private economic interests come at the expense of marine environmental damage.

Sweden has adopted environmental discounts for ships arriving at fairways and in some ports to encourage investment in measures to reduce shipping’s impact on climate change, air quality and marine environment. The present study investigates the impact of these discounts in 2020 on investment decisions made by ship-owners. As a starting point, this impact was assessed by comparing the potential annual benefits of the discounts with the annualized costs of retrofitting four selected abatement technologies.

The results indicate that, while the port discounts are relatively small when compared to the costs of abatement, the fairway discounts could be significant for ships frequently calling at Swedish ports under specific conditions. However, we conclude that the discounts alone are insufficient to incentivize ship-owners to invest in abatement technologies for older ships. To improve the usefulness of these discounts, the design should incorporate a more precise internalization of abatement costs. This could be achieved by implementing individual discounts for different abatement strategies, establishing dedicated subsidies for high-cost innovative technologies, enhancing scoring systems, and by better matching the discount with other market-based policies internationally.