Fundamentals of noise and vibration control

Designing a beautiful yacht is one half of the battle, but noise and vibration control can make or break the success of a new build yacht.

It's in the details

Noise and vibration control on board ships and luxury yachts can be a big problem for owners and operators, causing great discomfort and annoyance to crew and passengers. At the Monaco Yacht Show (MYS) 2014, Lloyd's Register (LR) Consulting demonstrated how, at the design and build stage, the use of noise and vibration prediction and measurement tools can help to minimise the risk of them occurring once the yacht is in use.

The shaking marine floor mounted with steel rods and colourful balls (or moveable weights) in the below video is a good way to illustrate some important fundamentals of noise and vibration on board superyachts and the ways in which they can be controlled.

Video: Rasmus Lyngdal-Christensen - Noise, Acoustics and Vibration Specialist, LR Consulting

Lloyd's Regsiter Consulting explained that the idea behind the shaking floor is to illustrate what happens when a natural frequency of one of the rods is excited; a standing wave is formed within the rod, which means that the vibration amplitudes of the rod increases dramatically at some positions, while at other positions there is no movement. By simply moving the ball on the rod, the natural frequency of the rod shifts away from the excitation frequency thereby reducing the dramatic vibration of the rod.

An intriguing example faced was a distinct low-frequency noise heard in the wheelhouse and in owner’s stateroom on a yacht. The noise appeared from time to time and sounded like a diesel generator exhaust, however, the wheelhouse and owner’s stateroom was located far from any of the diesel engines or exhausts. After some scrutiny, LR was able to verify that the noise only appeared during certain wind speeds.

After thorough testing, different measurements and analysis the noise turned out to be caused by wind-induced excitation of the terrace handrails in-front of the owner’s stateroom located above the wheelhouse. The wind caused vortex-shedding at the handrails that at certain wind speeds excited the first natural frequency of the handrails. By simply filling the handrails with sand LR was able to sufficiently decrease the natural frequency (moving the ball) without visually impairing the handrails, hence elegantly solving the noise issue.

For more information, visit Lloyd's Register.

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