The vibrations and acoustic comfort of a boat are often equated with insulating panels, as if these on their own can protect us from the disturbance of the noise generated by the engines. What a shame that “the noise” can find alternative solutions
by Francesco Michienzi and Luca Sordelli
It’s easy to say noise, but what produces noise on board large yachts? What can one do? And, above all, how can one prevent it? Gian Piero Repetti from Vulkan Italia, which has been working on these issues for more than twenty years, answers our questions.
Reliability and comfort are the two guiding principles behind the design of large yachts today. And comfort is mainly achieved by working on two aspects, stability and quietness. Do you agree? Is this what owners want?
The boating world has matured. The idea of transferring the “automobile” status symbol to the sea by means of a boat is rather superseded. So the goal is no longer to have a yacht with super performances to show off or to race out of the port. People want to experience the sea, be on board and enjoy the trip. Reaching the destination fast is not the point. At this stage it is clear that living on board in pleasant conditions has become much more important. So yes, more stable and less noisy boats are required.
When one talks of noise, one often thinks that all it takes is insulating the engine room properly to solve all problems…
To solve the problem one must be clear about some key concepts. First of all, one has to take into account how noise travels on board a boat: it travels not only through the air, but also through the structure.
What do you mean by through the structure?
The source of noise makes the structure move, it makes it vibrate. This vibration transmits itself to all parts of the boat, without being affected in any way by any insulation there may be. The insulation only serves to “solve” a certain type of noise, noise that is transmitted at high frequencies. It is done with the use of acoustic panels and other types of insulation. But this kind of approach doesn’t do anything to the structural line.
Can you give an example?
Let’s take for example a boat in which the main source of noise is the engines. In this case the high frequencies are transmitted to other areas through the walls that enclose the engine room. So with good insulation, one can avoid this kind of noise transmission. But there is still the fact that noise created by low frequencies is still transmitted by the structure. And so another type of approach is needed.
What type of approach?
One must insulate the sources of noise with adequate systems with elastic supports, transmission couplings. Or with local modifications, so that the structure can react and not be “subjugated” by the engine.
Who is responsible for these modifications? The shipyard?
First of all they depend on the awareness of the owner, who must be aware that to solve this problem it must be addressed in all its complexity and the shipyard at this point must work on prevention studying an effective insulation system. All are involved in the boating industry: owners, shipyards, engine makers, designers… Obviously this work has a cost, so the goal cannot be limiting the final price.
On this subject, how do you feel international shipyards approach this?
It depends on the country. The Netherlands is a good example, making products of extremely high quality where a lot of attention is given to comfort on board. In Italy it varies from one shipbuilder to another. Some are more aware of the issue, others less so. Some even experiment, while others try to follow the current. Overall the added value of this type of approach is recognised. In America however, they have always preferred to build reliable, functional and strong boats, but their solutions to noise comfort are in my view a step behind other builders in the same category.
At Vulkan, do you intervene both at a prevention level on the project and later on the finished boat?
Vulkan has been addressing these issues for twenty years now, looking at the problem of vibrations and noise in its entirety, not only in relation to the product it is supplying. When we are asked to intervene at the early stages, as prevention, we can evaluate the initial project. From a theoretical point of view, we are able to establish what is necessary for a good final result. We create a full acoustic audit of the boat. As to subsequent work, Vulkan can do “truble shooting”. So it can evaluate the problem starting from measurements taken directly on board and analyse the possible causes for noise and vibration, so that the problem can be outlined and we can offer solutions.
Can you give us a particularly impressive example of your work?
One of our first projects was a classic “Truble Shooting” problem for a charter sailing boat, about 58 feet long, where the problems arising from the propulsion were such that the owner could hardly offer his boat as a charter to clients. We carried out measurements on board and found that the main source came from the linking of the engine block to the boat, and carried out work to improve the insulation of the structure by modifying the connection between the engine and the inverter turning them into “a single block”. We did this without making any changes to the surrounding areas and without changing the overall size.
Do you also work on mass production?
We’ve done some work with more or less all the major Italian shipyards, especially at a prevention stage. In some cases we have even worked on the prototype with the shipyards design office, changing one parameter at a time trying to obtain a suitable result.
And as later work?
We work intensively on the possibility of vibrations via the structure, checking elastic supports, couplings etc. But not only that. We also check the structure of the boat. The base for a good result is the right surrounding environment. For example, an elastic support with a rigidity close to that of the boat will never work; so it is necessary to find a balance between the supplied products and the environment they will be applied in. We have worked on boats of various sizes, starting from 45 – 50 feet up to mega yachts. We have also done some interesting work on a cruise ship, in America, to increase the liveability of spaces using an energy recovery system of the exhaust gasses. The cabin around the chimney were totally unusable, but thanks to targeted modifications, during the refitting we managed to create more space on board.
Is there a difference between the various materials used to build a boat that influence the vibrations?
Definitely. To insulate vibrations or to lessen them, one must have mass, weight. It is much easier to work on a boat built in steel than on one built in carbon fibre where it is difficult to isolate or locate vibration because it is easily transferred to the boat thanks to the lightness of the structure.
So we are always in a world of compromise…
But it is also true that those who look for lightness do it for one reason: they do it because they want to go fast. This is a different approach to the issue: nobody expects to sail at 40 knots in perfect silence. It depends on what people are looking for when they go to sea.
Much has changed over the years. Previously, not that long ago, owners wanted large American motor boats with super engines with open exhausts. Is this unthinkable nowadays?
Rather than unthinkable, it is a niche market. A small category of clients certainly still enjoy the pleasure of hearing the roar of 12 cylinders with an open exhaust. But the notion of sailing in silence is much more popular. It comes, fortunately, from greater love for the sea.
Comparison sheet noise measurement while sailing
(Gian Piero Repetti – Vulkan Italia, the strength of the ideas – Barchemagazine.com – November 2017)