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92 | NOISE & VIBRATION

New technology cuts vessel noise and vibration

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ew technologies and procedures mean that noise and vibration levels within ships are lower than ever before. A main reason behind their reduction is from the increased use of hydrodynamics calculation software, RINA Services marine chief commercial officer, Paolo Moretti told Marine Propulsion. He explained that this allowed simulation of vibration coming from the shaft line and thus allowed the ship to be optimised to minimise pressure forces and cavitation from the propeller. Mr Moretti explained that the application of hydrodynamics software was also “very helpful” if noise and vibration became an issue once the ship was constructed and in operation, as the model could be looked at again and modifications applied. He said that this had been the case on a ferry that RINA had dealt with this year, whereby the bow thruster's motor had been causing too much vibration. “By using our stored model of the ship, we had the possibility to study where the pressure pulses were coming from and analyse it.” Based on this, RINA could see that the electric motor was not properly attached to the structure, thus creating vibrations. Stiffeners were inserted and the problem was solved. Mr Moretti said that this type of problem could be particularly important on cruise ships as it affected the comfort of the cabins at the stern and bow of the ship, where the most expensive cabins are placed. Elsewhere Abeking & Rasmussen (A&R) has entered the luxury expedition cruise ship market with a design

Hydrodynamic calculations, SWATH technology and an increased focus on cutting noise from HVAC piping systems have led to a reduction in noise and vibrations

using a small waterplane area twin hull (SWATH), which boosts passenger comfort by reducing motion as well as noise and vibration. It has launched Luxury Cruising, a 95m boutique ship concept. A&R naval architect and sales director of special vessels Nils Olschner explained the SWATH concept: “The buoyancy – the volume that is carrying the vessel structure – is taken below the waterline, so it is removed from the energy and not excited by waves. If it is not excited, then it does not move.” He explained that it reduces noise and vibration because the diesel engines are down in the torpedoes as well as most of the other

noise-making equipment, where there are no passenger spaces or any accommodation areas directly neighbouring these compartments. “The pure distance between the accommodation and technical spaces reduces both noise and vibration,” Mr Olschner said. Indeed, the shipyard has proof of that as it has built the same ship with the same engine installation in two different ways: on one ship the engines are on the main deck level, on the other they are down in the torpedoes. Noise and vibration carried through vessel piping systems is a challenge for ship operators – and there has been an increased interest in how to reduce the impact of those coming from

Victaulic’s grooved mechanical pipe-joining couplings reduce the noise and vibration of pipes within the HVAC system

Marine Propulsion & Auxiliary Machinery | August/September 2017

HVAC system pipes. Victaulic vice president maritime services Didier Vassal singled out this trend and highlighted how the company had recently been contracted to supply its grooved mechanical pipejoining couplings and fittings to the pipes of the air conditioning systems across the river cruise vessel fleet built in German and Belgium shipyards. Mr Vassal said “In mechanical rooms, pumps, chillers, heat exchangers and boilers frequently create noise and vibration which can be difficult to contain. Rubber bellows are often misaligned and fail to deliver the expected noise and vibration attenuations. Three Victaulic flexible connections will do the job”. Victaulic produces a grooved coupling pipe joining system that enables the gasket to seal against the pipe, while the ductile iron housing provides both space for the elastomeric material to flex and containment to prevent overstretching. Each joint is a union and the more couplings installed the better the noise and vibrations will be absorbed. Mr Vassal emphasised how there has been a lack of awareness in the industry about the use of grooved coupling pipe joining systems on HVAC systems. For the past 30 years pipe outlets of chillers have included a groove for the insertion of the coupling pipe system. But there is a lack of knowledge by marine outfitters about what this groove is used for – leading to the bypassing of grooved couplings and the use of older methods, such as the use of welding, flanges and conventional rubber bellows. MP

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Marine Propulsion & Auxiliary Machinery August/September 2017  

Marine Propulsion & Auxiliary Machinery provides the technical, operational and project teams that work for the ship owner/operator/manager...

Marine Propulsion & Auxiliary Machinery August/September 2017  

Marine Propulsion & Auxiliary Machinery provides the technical, operational and project teams that work for the ship owner/operator/manager...