Cutting Noise And Vibrations in Superyachts With Smarter Engineering

Future-proofing yachts

This new generation wants “access all areas”, but certain types of vessels are banned from marine reserves and clean ports in order to prevent pollution. The industry is pre-empting legislation and these demanding new clients are accelerating progress towards cleaner yachts with lower emissions in terms of exhaust (particulate or gaseous) and noise. These new vessels are more efficient in every respect, from materials to operations.

Anybody commissioning a newbuild would be wise to go beyond current legislation as new local regulations will otherwise undoubtedly prevent them from cruising in certain destinations in the future, even if the vessels were originally built within the rules. For instance, Norway’s UNESCO-protected “Heritage Fjords” will only allow zero-emission vessels to sail in them from 2026.

How to tackle decarbonization challenges

DNV offers myriad decarbonization services and insights, not least through their Maritime Forecast to 2050 report series, focusing on shipping’s decarbonization pathways. DNV now offers its expertise to the superyacht industry – even to non-DNV-classed vessels – through independent advisory and compliance services.

Reducing energy consumption is a good starting point considering that approximately half the energy use on a superyacht is from “hotel load” (on-board air conditioning, lighting etc.) and only half from actually propelling the vessel, where hydrodynamics and propulsion systems come into play, along with fuel type. Figures for the percentage of hotel load versus propulsion load in the superyacht industry are being compiled by the Water Revolution Foundation.

Hybrid yachts allow sufficient flexibility

DNV expert Erlend Nervold, Principal Engineer, Machinery ＆ Systems at DNV, believes hybrid yachts will prevail in the immediate future, with diesels still proving popular but hybrids having the significant benefits of being quiet and clean in port.

Newbuilds are easier to plan for as engine room spaces can be designed for the required machinery and the fuel tank capacities integrated, but “normally there is room to implement hybrids on existing boats too”. There are several fuel options to consider, all of which will need close consideration along with tank arrangement, material use and future flexibility to provide the possibility to change to zero-carbon fuels when they become available.

Air lubrication increases energy efficiency

Nervold analyses both propulsion and fuel together as they go hand in hand: “Advances in energy savings reduce the power you need to produce.” He believes that air lubrication could be one idea to consider for some superyachts, the equipment not taking up too much space and the method already proven in commercial vessels, where air is pumped out through nozzles in the hull. It does tend to work better with larger flat-bottomed hulls though so is not suitable for slender hulls, which rules out some superyachts.

COSSMOS helps to test new machinery systems

Nervold believes that DNV’s COSSMOS complex machinery simulation methodology could also benefit superyachts when evaluating new technology options. “We can build up virtual systems to see where energy is flowing, where useful energy is lost, and where the main saving potentials are. For example, cooling systems are often ‘on’ or ‘off’, so most of the time are dumping a lot of water. If you install a smarter system, with a variable frequency drive, you can actually reduce the power needed for the cooling system according to demand.”

Cutting noise and vibration

As well as energy savings and cutting exhaust and particle emissions, noise and vibration is an area that has recently garnered more attention for two reasons. Firstly, the comfort of owners, guests and crew on board as well as people on adjacent yachts and in waterfront residences, enjoying peace and quiet. Secondly, environmental factors – which some might put first.

Noise pollution is considered to be a significant threat to life after climate change and chemical pollution. Largely overlooked until recently by the industry, DNV expert Stian Andreassen, Head of Section, Noise and Vibration at DNV, notes that younger, eco-conscious buyers, often also from a technical background, are driving change:

“They are more aware of the environment and more concerned about the impact of noise emissions. One can imagine younger, tech-savvy owners or charterers, more switched on to smart, silent propulsion, enjoying quietly passing by another yacht without being heard or silently cruising the same waters as a pod of dolphins or killer whales.”  

Finding the sweet spot for underwater noise emissions and propeller efficiency

Most of Andreassen’s work is on newbuilds. “There is room to improve the hydrodynamics of yachts. Underwater noise emissions are closely linked to propeller design, which needs to be considered during the build phase. Small changes can have impressively large effects on underwater noise.” Andreassen points out a not commonly known fact: “If you go too extreme on efficiency you’ll most probably arrive at a noisy propeller! You should aim at the ‘sweet spot’ with a combination of satisfactory underwater noise emissions and good propeller efficiency. 

Today, the large focus on the reduction of carbon emissions leads to extremely optimized propeller efficiency, but noise should not be neglected as this approach can lead to a very noisy propeller. Explorer-type yachts that will likely visit sensitive marine reserves in their lifetime should certainly focus on underwater noise emissions at the design phase.”

Economic incentives for noise reduction

DNV’s advisory services are not limited to newbuilds. DNV is often contacted when there is a problem on an existing yacht, such as propeller-induced noise. Follow-up tests might involve a hydrophone being submerged in the water and the yacht in question passing by while measurements are made, although a simpler troubleshooting option would be to install sensors in the hull above the propellers.

Andreassen is aware that incentives to reduce underwater noise in commercial shipping are mainly driven by the authorities in Canada, where noise disturbs marine mammals such as killer whales during the mating season. There are significant economic incentives for ships with low noise levels in Canadian waters. The EU aims to reduce underwater noise from anthropogenic sources through the implementation of threshold levels. It is also supporting efforts to reduce noise pollution by aiding large research groups working on underwater noise and its impact on marine mammals.