Noise and vibration on maritime vessels

On maritime vessels, noise and vibration are not the same but they have the same origin and come in many forms. The methods to handle the related problems are similar, to a certain level, where most shipboard noise problems are reduced by controlling vibration.

Sources

The main producers of mechanically created noise and vibration are the engines, but there are also other sources, like the air conditioning, shaft-line, cargo handling and control equipment and mooring machinery.

Diesel engines

When looking at

Electrical engines

Large vessels sometimes use electrical propulsion motors, the electrical power being provided by a diesel generator. Noise and vibration of

Turbines

Steam turbines and gas turbines, on the other hand, when new and/or in good repair, do not, by themselves generate excessive vibration as long as the turbine blades are in a perfect condition and rotate in a smooth gas flow. But after some time microscopic defects appear and cause small pits to appear in the surface of the intake and the blades which set up eddies in the gas flow, resulting in loss of performance and vibrations. Vibration levels may change with different loading conditions or when doing a manoeuvre.

Other sources

Besides mechanical produced vibrations, other sources are caused by the motion of the sea, slamming of the vessel on the waves and water depth to mention just a few. The main problem here is that they are less controllable.

The engine-gearbox interaction is usually a source for noise and vibrations. Here, it can be installed highly flexible couplings between the engine and the gearbox. These type of couplings are used because of their low torsional stiffness.^[1]

Exposure limits

Exposure to noise and vibrations is regulated and limits for maritime vessels are given in the ISO standard 6954: Guidelines for permissible mechanical vibrations on board seagoing vessels to protect personnel and crew.

Because there are different noise regulations from country to country, the International Maritime Organization (gago) sets some standards for vessels. The table below gives some comparisons of preferred maximum noise levels on board of vessels and onshore levels.

Noise and vibration control

Noise generated on board ships and submarines can have far-reaching effects on the ability of the vessel to operate safely and efficiently. Military vessels in particular need to be quiet to avoid detection by

Prevention

At the design table, the

In megayachts, the engines and alternators let out unwanted noise and vibrations. To solve this, the solution is a double elastic suspension where the engine and alternator are mounted with vibration dampers on a common frame. Then, this is mounted elastically between the common frame and the hull. While in megayatchs the requirement is the comfort of crew and passengers, in other applications, such as navy ships, the requirements involve that the engines or generators should work under certain shock loads. To achieve this the ships install double elastic suspensions and high deflection mounts are installed between the unit and base frame. Beforehand, the engineers calculate the torsional vibrations or the 6/12 degree of freedom to guarantee the optimum combination of couplings and mounts. ^[4]

Maintenance

Regular maintenance will have a major influence on the performance of instruments and machines. Lubrication of the joints, tightening of the bolts, good alignment of stern contour of the vessel, adjusting of variables following the weekly and monthly schedule are the most effective routes to noise and vibration control.

References

• Lloyd's Register Technical Papers; Ship vibration and noise: some topical aspects by J.S. Carlton and D. Vlašić
• International Maritime Organization

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