Quite often, when people are interested in buying a yacht, they first look at its exterior. After that, they check its general interior arrangement and then dive into its specifications. While the exterior, interior, and specs are all important, there are several other boat features that receive a lot less attention than they deserve. Noise and vibration are among these things. Noise and vibration don’t affect the way your boat looks or moves, but they are of critical importance when it comes to the comfort and safety of passengers and crew.
Spacious cabins, high ceilings, and ample storage space create a more pleasant boating experience. These features stand out. But to learn how well the boat is insulated against noise and vibration, you must use and observe the vessel. This use and observation should be prolonged because every boat behaves differently and has various noise and vibration levels while at anchor, at cruise speed, and at full throttle. However, if there is no possibility to test the boat in this way, one can also look at the specifications, in particular at the locations, thickness, and type of the insulating material. Whether you are looking to purchase or build your own boat, this article will tell you what is important to prevent onboard noise and vibration.
Vibration damping and sound insulation are essential because moving parts and external factors can cause vibration and noise. Waves, which are a dynamic force, engines, and HVAC (heating, ventilation, and air conditioning) systems are the main source of vibration and noise in a vessel. These all can affect comfort level and even the health of passengers and crew. Different types of isolators and absorbers are used to reduce these effects. These materials not only reduce structure-borne and air-borne noise and vibrations but also protect vibration-sensitive interiors or fittings. A proper noise and vibration evaluation is an important issue for this reason. (Aydin 2016).
Noise is an unwanted sound considered unpleasant, loud or disruptive to hearing. The difference between sound and noise depends upon the listener and the circumstances. For example, the sounds made by crickets in the evening can help make a romantic moment perfect, but can also potentially drive people mad if they are trying to fall asleep. Engine revving at the race track pleases the crowd in the stands, but if you are trying to have a phone conversation, the sound of your neighbor’s loud motorcycle creates unwanted noise.
It can be hazardous to a person’s hearing if the sound is loud and if they are exposed long and often enough. Sound is produced by vibrating objects and reaches the listener’s ears as waves in the air or by other media. When an object vibrates, it causes slight changes in air pressure. These air pressure changes travel as waves through the air and produce sound. (OSH 2019).
Depending on how it changes over time, noise can be:
– Continuous, remains constant and stable over a given (long) time period
– Variable, when different operations or different noise sources cause sound changes over time
– Intermittent, if there is a mix of relatively quiet and noisy periods
– Impulsive, also called impact noise, is a very short burst of loud noise which lasts for less than one second.
Vibration is defined by the Merriam-Webster dictionary as a periodic motion of the particles of an elastic body or medium in alternately opposite directions from the position of equilibrium when that equilibrium has been disturbed (as when a stretched cord produces musical tones or molecules in the air transmit sounds to the ear). Vibration can be desirable; however, in many cases, such as in boats, it is undesirable, wasting energy, and creating unwanted noise and other negative effects.
Vibration and noise are generated in the same way and generally from the same sources, the difference being the way they are perceived by the observer.
Vibration involves frequencies in the range 1 – 80 Hz.
Noise is in the frequency band from 20 to 20,000 Hz which the observer hears as sound. (Tupper 2013).
Therefore, the studies of sound and vibration are closely related, and attempts to reduce noise are often related to issues with vibration.
– Low-frequency, is created by vessel motions, which are produced by various sea states in conjunction with vessel speed and point of sail.
– High-frequency, is often associated with rotating machinery.
– Single-impulse shock loads are induced by vessel slamming, which may be caused by dynamic impact loads being exerted on the vessel’s bottom or bow flare due to vessel size, speed, and wave conditions.
There are three primary reasons for using various types of noise and vibration insulation on a boat. First, it is to create a more pleasant boating experience. Second, since the noise and vibrations can turn into a health and safety issue and might have serious adverse consequences, the insulation also plays an important hazard prevention role. Third, noise and vibration reducing tools must be used not only to minimize the problem but also to fulfill the regulations such as “comfort class”. (Aydin 2016).
Regulations about onboard noise are issued by a number of international and national bodies. Standards for vessels and working conditions were created by the International Maritime Organization (IMO), the International Organization for Standardization (ISO), the International Labor Organization (ILO), the American Bureau of Shipping (ABS), and a number of other Classification Societies, to name the most important ones. This variety of rules between these bodies makes the noise and vibration regulatory field quite stratified and tangled. Below are short overviews of several such documents.
The first key document establishing requirements in the field is the Code on noise levels on board ships issued by the IMO. It formulates norms and requirements to limit noise levels and to reduce the exposure to noise. The goal of this document is to prevent communication problems, which may cause danger, to protect seafarers from hearing injuries, and to provide them with an acceptable degree of comfort in rest and recreational spaces. The main focus of the IMO Code is on preserving the health of the onboard workers. (Badino 2012). To compare, below are the preferred maximum noise levels on board vessels as compared to onshore.
|Area||Noise limit land (dB)||IMO noise limit (dB)|
The ISO also sets standards for vessels. The exposure to noise and vibrations is regulated and limits for maritime vessels are given in the ISO 20283-5:2016 Guidelines for measurement, evaluation and reporting of vibration with regard to habitability on passenger and merchant ships. It gives guidelines for the measurement, evaluation, and reporting of vibration with regard to habitability for all persons on-board the passenger and merchant ships, especially for crew.
Comfort levels on modern superyachts have recently been the object of specific attention for various Classification Societies that have issued new rules and regulations for evaluating noise and vibration maximum levels. These rules are named “Comfort Class Rules” and set the general criteria for noise and vibration measurements in different vessels’ areas, as well as the maximum noise and vibration limit values. As far as vibration assessment is concerned, the Comfort Class Rules follow either the ISO 6954:1984 standard or the ISO 6954:2000. (Pais 2017).
The ILO has ratified the Maritime Labor Convention (MLC). This Convention provides legal instruments aimed at protecting and improving working and living conditions for passengers and crew. It outlines the, as yet, most comprehensive Code regarding seafarers’ rights, and the obligations of States and shipowners with respect to these rights. The Convention incorporates the fundamental principles of many ILO Conventions and brings together and updates 68 existing ILO instruments (Conventions and Recommendations) into one document.
Same governing bodies regulate the vibration through the aforementioned guides. The newer addition of ISO 6954 standards was published in 2000 and sets the baseline for the Comfort Class Rules of the major Classification Societies. Also, the ABS has introduced its Guidance Notes on Ship Vibration in 2021 to provide users with specific guidance on the design, analysis, measurement procedures and criteria in order to achieve the goal of limiting the ship vibration to an acceptable level. This document adds to the 2019 ABS Guide for Comfort on Yachts establishing COMF(Y) and COMF+(Y) levels of vibration comfort. Bureau Veritas, Det Norske Veritas, Germanischer Lloyd, Lloyd’s Register, RINA and other Classification Societies follow the case by producing similar roles for the assessment of vibration comfort levels.
Ultimately, the body of regulatory framework is intended to assist the marine community (shipyards, designers, regulators, and owners) to address noise and vibration issues. Some of these documents, such as the ILO’s, are legally-binding to states and shipowners, while others provide a set of recommendations for strong consideration when designing any new vessel in order to provide the safest and most productive working environment for seafarers.
As noted above, work-related hearing loss and vibration-related health effects are critical workplace safety and health issues. Adverse/improper noise and vibration levels can cause speech interference, mask warning signals, interfere with concentration and thought processes, disrupt sleep, and create harmful living and working conditions. If designed appropriately, however, vessels complying with proper noise and vibration levels can provide an environment for improved crew performance, safety, comfort, and communication, and have an overall positive psychological effect on seafarers. (ABS 2017).
As an example, a study that examined crews working under conditions of higher noise and vibration exposure, found that people have worked overtime, slept less than necessary and, generally, did not observe the official program. The daily personal noise exposure (LEP,d = 92 dB) and vibration levels during an 8-hour working shift (A(8) = 4.1 m/s2) also caused increased body temperature and blood pressure. This has reduced crewmembers’ work capacity and attention levels. (Picu 2019).
The prevention of noise and vibration issues can be done in several ways, from predicting the noise levels at the design stage to installing specialized equipment and providing anti-noise and anti-vibration treatment to different parts of the boat. Careful consideration should be given to designing noise and vibration reduction elements because in some cases the cost of fixing noise or vibration issues can be as much as ten times more expensive after construction than if incorporated into the design from the preliminary design stage. Different anti-noise and vibration tools and how they are implemented in marine construction are covered in the second part of this article. It will also present a case of noise and vibration testing of one of Bering boats, which is a standard procedure performed for all the vessels produced by Bering.
1. American Bureau of Shipping (ABS). Noise and Vibration Control for Inhabited Spaces. 2017.
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