On Friday the 3 July 2026, the International Chamber of Shipping (ICS) hosted a webinar on ‘Efficient and Quiet Technologies for Ships.’ These technologies are becoming increasingly important as the industry seeks to improve performance and reduce environmental impact. ICS’ Principal Marine Director, John Stawpert, moderated this discussion, with Associate Professor at the University of Genoa Stefano Gaggero, Director Hydrodynamics at Kongsberg Hydrodynamic Research Centre Göran Grunditz, Naval Architect at Fincantieri Alessandro Marino, Senior CFD Specialist at Lloyd’s Register Savas Sezen, and Technical Director at ICS Chris Waddington, making up the speakers on the panel.

The webinar opened with Chris Waddington giving an overview of efficient and quiet technologies. He broke his presentation down into three sections: why, how, and when. Starting with the ‘why,’ he explained that the industry is already moving towards better energy efficiency with international regulations in place, however, the concerns surrounding underwater radiated noise (URN) are less well-known. Underwater radiated noise (URN) can pose a significant threat to marine life. By producing a background ‘hum’ of URN, it hinders their ability to hunt and communicate, which may leave them without food and disorientated in the ocean. He provided the analogy of humans struggling to hear each other next to a noisy road.

He then explained ‘how’ we can make changes. Generally, there is a synergy and clear correlation between energy efficiency and reducing URN. For example, wind assisted propulsion has the purpose of improving energy efficiency, but as a knock-on effect, it also reduces URN. There is therefore a large opportunity to ensure URN is being reduced, simply as a co-benefit of implementing the energy efficiency measures.

Lastly, turning to the question of ‘when,’ Chris explained that Shipowners are already adopting energy efficiency measures, and this activity will only increase in the future. If the industry considers URN in parallel with energy efficiency, then its reduction becomes very straightforward. If energy efficiency is considered in isolation, it will become a lot more difficult to retrofit ships for URN reduction in the future. Therefore, the time to act is right now.

The webinar turned the conversation to Stefano. He was asked to give an overview of cavitation, including what it is and why it creates so much noise. He explained that cavitation is initiated on the forward side of the propeller where the pressure drops sufficiently for bubbles of water vapour to form. As the bubbles are swept to the aft face of the propeller, they suddenly enter a high-pressure area where they collapse, and release energy in the form of intense Underwater Radiated Noise (URN).

Although propeller cavitation is the primary cause of URN from ships, Alessandro shared insights into other sources of URN, including hydrodynamic noise generated by the flow of water going around the ship, machinery noise, and propeller singing.

The conversation turned to Savas, who was coming into the webinar after publishing Lloyd’s Register’s guidelines on propeller design. He was asked to summarise his recommendations on how to reduce URN whilst improving energy efficiency. He echoed Chris’ earlier point, that they should be considered together, not as separate objectives. He stated that improving propulsion can reduce URN, so they would recommend starting with the fundamentals, such as maintaining a clean hull and propeller, managing biofouling, and ensuring the propulsion system is operating efficiently. He also noted that each vessel is different and will require different methods of optimisation to reduce factors like cavitation. He recommends taking a holistic approach, firstly understanding how the vessel operates and then optimising the propeller to suit that vessel. Our moderator, John Stawpert, responded to Savas, highlighting the significance of biofouling, with it being discussed and considered at the International Maritime Organization (IMO) at the moment.

Göran has real-world experience on propeller upgrades on the RoRo ferry, the Baltic Queen. Therefore, he shared some key points from this upgrade. Although originally designed to operate at 24 knots, the ship owner had slowed the vessel to the extent possible within the service requirements. Realising that the propeller was no longer optimal for this speed, the blades were redesigned by Kongsberg. Fuel consumption and URN were measured before and after the retrofit, which found there were substantial improvements in both.

With all the individual presentations complete, the second half of the webinar was dedicated to a Q&A from the attendees. Firstly, Stefano was asked why there is a conflict between efficiency and URN with fixed blade propellers. He explained that this is due to the hydro blade-loading, for example, relatively large blade areas reduce the pressure differential across the blades and therefore reduce the risk of cavitation induced URN, whilst also reducing efficiency due to increased hydrodynamic drag.

Next, Göran was asked about controllable pitch propellers, with a question surrounding why the reducing of revolutions for fixed bladed propellers improves fuel efficiency and reduces URN, but it increases for Controllable Pitch (CP) propellers. Göran stated that as long as you operate with a constant pitch, a CP propeller will behave the same as a fixed pitch propeller. However, under normal operation, such propellers are operated at constant shaft revolutions per minute (RPM) and speed reduction is achieved by reducing the pitch, which can make the propeller noisier. Although the impact of this can be mitigated by adjustment of the combinator curves (i.e. the curves which define the relationship between RPM and pitch for a propeller).

Alessandro was also asked how a fixed blade propeller can be designed to get the best compromise between efficiency and URN reduction. He shared that a propeller must work well with its own ship. When designing a propeller, the key thing to consider is the overall design of the ship, for example considering what conditions the propeller is going to work in. In order to have a holistic approach to the design, you must consider the wake before the propeller. This can be optimised by optimising the hull shape for low resistance, therefore ensuring you do not overload the propeller. He listed some more factors, including keeping the centre of buoyancy as far forward as possible, optimising the blade number (e.g. typically six for cruise ships), and optimising propeller design with low tip vorticity, etc. Therefore, it is not solely down to the propeller’s design, and for new ships there is also benefit in optimising the hull.

The next question asked, aside from propellers, are there any devices or techniques that can simultaneously improve energy efficiency and reduce URN. Savas responded first, stating that whilst propeller optimisation is the main contributor, there are other factors such as reducing hull fouling, ensuring the steady flow of water into the propeller, slow steaming, air lubrication, and more. The simple ways would be maintaining hull cleaning and managing biofouling, which will benefit fuel consumption and in-turn, reduce URN. Chris jumped in after, explaining that Savas had covered a lot of the factors. He highlighted that the sheer length of the list is key in seeing the opportunity to reduce URN. Whilst there is a lot to do with the propeller design, there is also a lot that can be done around the propeller, such as fitting propeller boss cap fins, or ensuring a clean wake flow with flow straightening devices. He shared some extra potential measures, which can be as simple as routinely cleaning the propeller. He added, in relation to the speed of the ship, when it drops below 10-12 knots, the cavitation inception speed is reached, and cavitation induced URN effectively disappears. He gave one example of an environmental incentive scheme in Vancouver, Canada. This includes a list of devices which are known to reduce URN, and if a ship can prove that they are using them, then they receive reduced port fees, thereby introducing an economic benefit.

Chris did note that simply decreasing speed on its own may be counter-productive, as slower moving ships could create issues with capacity, where more ships will have to be built to transport the same quantity of goods. Nevertheless, implementation of Just-in Time Systems such as Blue Visby could be effective in eliminating port waiting time and thereby reduce speed to the maximum extent practical without diminishing cargo capacity.

Chris was asked about the current URN-related work at the International Maritime Organization (IMO), as well as what work is being planned for the future. Chris shared that three years ago, IMO updated their URN guidelines, with a significant aspect being that each ship should have its own noise management plan. These guidelines are within an experience building phase and efforts are ongoing to increase the uptake of these measures. Looking into the future, there is a proposal to carry out a global study on ambient levels of URN under different scenarios. He also highlighted the difficulty of measuring a ship’s URN, and the high cost to do it (typically 30,000-50,000 dollars per ship). Therefore, more economical and accessible ways of recording URN are being considered.

As the Q&A wrapped up, John asked our panel to each state the key points they would like the attendees to take away from the webinar. Each speaker seemed in agreement, that we must take a holistic approach and consider energy efficiency and URN as one moving forward, and it is important to optimise in tandem. Chris stated that with the industry’s increasing adoption of energy efficiency measures, the opportunity to leverage synergy between both is here and now. He reminded us that for the Baltic Queen, it was as simple as installing more appropriate propeller blades, which increased fuel efficiency by 15% and reduced URN by up to 8 dB, so the solutions do not need to be overly complex. We were also reminded of the vital importance of reducing URN, as it is having a detrimental impact on the environment and marine wildlife. By taking the necessary steps now, the opportunity is there to readily make a difference.