Page 44: of Marine Technology Magazine (April 2013)

With increased focus on the negative impact of subsea noise on the marine environment, regulators are considering action. Until then, different stakeholders are working together to develop a range of technical solutions to manage the issue. Over the past decade, regulators have sought to manage the impact the shipping industry has on the environment by in- troducing legislation covering ballast water treatment, restric- tions on substances used in marine coatings and carbon emis-sions, among other issues. However, while subsea noise has long been recognised as a threat to marine life, there has been little action to manage the issue. That may be changing. Last year, the IMO?s Sub-Committee on Ship Design and Equipment established a correspondence group on reducing commercial shipping noise through non-mandatory technical guidelines. The Committee identi ed four focus areas for noise reduction: propulsion, hull design, onboard machinery, and operational modi cations. In Europe, the EU Marine Strategy Framework Directive is working with University researchers to assess noise pollution and de ne baseline levels of underwater noise. Once complete, the EU plans to introduce legislation setting standards to reduce noise levels by 2020. At the same time, the US-based National Oce- anic and Atmospheric Administration (NOAA) is working on a global project to document human-generated subsea noise to create the world?s  rst sound maps. In the meantime, most of the work to develop quieter ships so far has been driven by owners with commercial or scien- ti c incentives to reduce subsea noise. According to DNV?s Kai Abrahamsen, Principle Engineer (Noise and Vibration), interest in this specialist  eld is growing. ?Our work in this area has been con ned to vessels active in seismic surveys, scienti c research, commercial  shing and government-relat- ed naval projects. But we have also been engaged by energy companies, who seek to shield sensitive acoustic instrumenta- tion related to sub-sea construction and communications from underwater noise,? he says. ?We are encouraged by NOAA?s focus on subsea noise and statements made by the IMO and the EU suggesting that action may be taken to apply new stan- dards for merchant vessels, which produce the most noise.? Abrahamsen explains that low frequency sound waves can travel for hundreds of kilometres underwater before they dis- sipate, upsetting the highly evolved hearing abilities that  sh and sea mammals (especially dolphins, whales and seals) rely on to hunt and communicate. ?Reducing noise and vibration can be a complex engineering challenge, but we are seeing specialists in different areas working together to develop some highly innovative technical solutions,? he says. ?A lot of sub- sea noise generated by ships can be traced to propellers, but some industry players are turning their attention to another signi cant contributor ? engine vibration.? Water is an ef cient conductor of sound and engine and propulsion noise is ampli ed by a vessel?s hull. Underwater noise results from airborne noise, which is generated from the machinery to the structure of the vessel, and structure borne noise, which is generated from the vibrations of the machinery to the hull of the ship. To minimise this noise, engineers must consider a broad range of issues, including engine and genera-tor mounting systems, base frames, materials and the position of isolators. One company working with noise and vibration is Pon Power Scandinavia, a leading distributor of Cat and MaK marine propulsion systems. In 2008, Pon Power began work on a mounting system designed to isolate engine vibration of high-speed gensets. According to Pon Power?s Area Service Manager, Øystein Skår, the development of the Gen ex sys- tem was driven by the increasing power density of generator sets. ?Over the last decade, engine output has been increasing. As a result, generators can no longer survive the mechanical noise and vibration produced by many of the new, more pow- erful diesel engines,? he says. ?We identi ed a market for a mounting system that could reduce noise and vibration and be  exible enough to work with generators manufactured by different suppliers.? Pon Power developed a system where the generator is rig- idly mounted on easily adjustable chocks, and  exible mounts are  xed between the engine and base frame. Introduced in 2009, the Gen ex concept has attracted signi cant industry interest. ?The development process brought us into contact with a number of noise and vibration specialists around the world and has enabled us to carve out a strong reputation in a growing market,? he says. ?This has lead to our participation in some interesting projects within noise and vibration.? In 2008, Pon Power was asked by Siemens to provide gen- erators for a diesel-electric powered research vessel under construction at the Jong Shyn Shipyard in Taiwan. The vessel, ORV Aerial, was ordered by Taiwan Ocean Research Institute Noise Mitigation Quiet E ciency Working Together to Reduce Subsea Noise April 201344 MTRMTR #3 (34-49).indd 44MTR #3 (34-49).indd 444/4/2013 11:27:52 AM4/4/2013 11:27:52 AM