Noise and vibrations emanating from inboard boat engines are ubiquitous phenomena, affecting both passenger comfort and the durability of structures. Soundproofing has therefore become a major challenge for anyone wishing to improve the quality of navigation, while reducing the environmental impact of underwater noise. Today, various technologies and materials are available to effectively address this problem: here's an overview of the options available.
Engines, sources of pollution
Boat engines are often responsible for high noise levels, which can affect onboard comfort and even crew safety. These noises fall into two distinct categories:
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Airborne noise is that which propagates through the air, through the boat's bulkheads, doors and portholes. It is mainly caused by turbulence generated by moving engine parts such as fans, alternators and heat exchangers, as well as by the passage of air over surfaces such as air intakes and exhaust outlets.
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Structural noise, on the other hand, is transmitted directly through the boat's hull, via engine vibrations that are absorbed by the boat's structure. This phenomenon is particularly marked with powerful engines such as those used in large speedboats, where low-frequency vibrations are stronger and propagate more rapidly. These low frequencies, due to heat engines and propulsion, are rapidly transmitted through materials such as fiberglass or metal, causing a resonance that can spread throughout the boat. Structural noise is more difficult to control, as it is amplified by rigid walls and surfaces that act as resonators.
Acoustic comfort and fire safety
Among the most effective solutions for soundproofing boats are high-density foams and membrane products, which play a central role in absorbing and reducing noise. These foams are glued to all bulkheads (even the ceiling) in the engine hold.
Materials such as cellular PE foam, like Cellofoam's Cello D 2500, are of particular interest. Their excellent resistance to hydrocarbons makes them suitable for nautical environments, where petroleum products such as fuels and oils can be sprayed onto the foam, which must not absorb them, with the risk of fire. This foam is able to absorb noise effectively across a wide range of frequencies.
Another solution is Navicork by Amorim's ACM16 panels, made from recycled cork and rubber granules. These high-mass, multi-layer panels are specifically designed to dissipate vibrations and prevent their propagation through the boat's structure. Their ability to absorb airborne sound while remaining light and flexible makes them a perfect choice for yachting.
In addition to their acoustic and vibration performance, these materials are also of major interest in terms of fire safety. Various brands have developed specific acoustic foams for marine applications, incorporating fire-retardant properties into their products.
WAVER Tec acoustic foam from aixfoam, for example, is designed to meet stringent fire protection standards, an essential factor in the nautical sector for crew safety. The addition of flame retardants to these materials not only protects the boat's structures, but also ensures better risk management in the event of fire.
Towards active, intelligent solutions
In addition to traditional insulating materials, a number of technological innovations are paving the way for active solutions to reduce noise and vibration pollution. Among these, dynamic vibration absorption systems are enjoying growing popularity. One example of this technology is the use of magnetostrictive suspensions or magnetic fluid dampers, which instantly adapt to variations in vibration generated by the engine and surrounding conditions.
These solutions are already finding successful applications in industrial sectors such as automotive and aeronautics. Although some systems, such as the Vibration Damping of Helwig Carbon Products focuses on reducing vibrations in industrial engines via conductive materials, there is potential to explore these technologies in the marine sector, particularly for improving the comfort and performance of luxury yachts and high-end sailing boats.
Another major player in the field of active vibration control for marine applications is PiezoMotor. This technology uses piezoelectric actuators to control vibrations with high precision in real time. These actuators, which expand and contract under the effect of electric fields, ensure reactive and precise adjustment to vibrations at different frequencies. These systems are particularly effective in reducing mechanical noise and optimizing engine and propeller performance on yachts.
Similarly, Galfenol, a magneto-sensitive material first produced over 20 years ago by the US Navy and developed by companies such as American Magnetics, is a cutting-edge solution. This material reacts to external magnetic fields and converts mechanical vibrations into electrical energy, providing an energy-efficient method of reducing vibrations. This energy can then be used to power other system components or be stored. The advantage of Galfenol lies in its robustness and ability to operate over a wide temperature range.
Boat engines mainly use more traditional materials for vibration damping, such as mechanical dampers or viscoelastic materials. Galfenol, on the other hand, is a more recent and innovative solution, which could be used on a wider scale in the boating sector.
Choosing composite materials to reduce vibrations
Composite materials, used in the construction of boat hulls, also offer considerable advantages in terms of sound and vibration insulation. By combining these materials with acoustic foam or panel solutions, it is possible to create a boat hull offering superior insulation against noise and vibration.
Some naval architects are incorporating optimized design concepts aimed at minimizing noise propagation by modifying the hull's resonance zones. For example, by modifying wall thickness at strategic points or using multi-layered structures, it is possible to create hulls whose resonance is absorbed before spreading throughout the boat.
Architects specializing in the use of composites for their acoustic and vibration properties include Eric W. Sponberg of Sponberg Yacht Design, who applies advanced composite material concepts to maximize performance while reducing vibration. Other architects such as Luca Santella and Michael Peters Yacht Design have also contributed to integrating these technologies into their modern yacht designs, often in collaboration with experts in nautical acoustics.
The search for solutions to reduce noise and vibration from inboard engines is more than ever at the heart of the concerns of yachtsmen and yachting professionals. Innovative materials and technologies today offer a wide range of options for improving onboard comfort, while complying with environmental and safety requirements. The move towards intelligent solutions could well shape the future of even quieter, more enjoyable boating for all.
