The Problem

Subsea piling for offshore construction projects generates considerable underwater noise, which impacts on marine mammals due to sound frequency and pressure levels. Yet large UK round 3 offshore wind development sites require significant numbers of piles and everyone involved in undersea work is aware of the potential environmental damage that such schemes can inflict.

As a consequence, gaining the approval of Marine Scotland or the Department of Energy and Climate Change is increasingly difficult — as it should be if we want our work to be both sustainable and acceptable to the general public. In addition, numerous environmental impact studies emphasise that sound reduction is essential if we want to significantly reduce the negative effect that undersea work such as this has on marine mammal habitats. And while Germany may be the only country that currently imposes noise limit regulations, others are bound to follow, either through government legislation or industry regulation, whether voluntary or compulsory.

The result of this shift of emphasis is that noise reduction may once have been a bolt-on luxury but has now become an essential consideration and component of any undersea project.

The Solution

The Noise Attenuating Piling Shield developed by Cairndene Ltd offers considerable advantages over existing noise mitigation technology, such as isolation casings, bubble curtains, cofferdams or hydro sound dampers. It is also superior to low-noise foundations like vibratory pile driving, drilled or gravity foundations and floating wind turbines.

NAPS uses a combination of air pockets and a vacuum chamber to significantly reduce the transmission of underwater noise. It can be applied at a wide variety of depths, attached to multiple bases and is therefore adaptable to differing seabed conditions. Critically, it has a modular design of interlocking rings, so if it becomes damaged you only need to replace the affected portion, not the whole structure.

The Construction

NAPS consists of inner and outer dual-skin pressurised air bags, within which is contained a vacuum. And as we all know from the movie Alien, in space, or a vacuum, no-one can hear you scream. This inner vacuum is both literally and figuratively the core of NAPS. It will be particularly applicable for large wind turbine projects but is adaptable enough to work successfully in any underwater activity that involves drilling or piling. It contains two metallic end rings and

“Noise reduction may once have been a bolt-on luxury but has now become an essential consideration and component of any undersea project”

as these are the only parts of the structure that will allow noise leakage, the reduction of damaging noise waves is considerable. These top and bottom rings, or modules, are designed in such a way that air and vacuum supply hoses and lifting and supply points are fully integrated (top), along with various foundations to cope with the different seabed conditions, such as gravity, suction or mud mat (bottom). The remaining rings in-between are identical and can be easily replaced.

The Advantages

The deck space required for storage is considerably reduced because of the lightweight construction and the fact that NAPS is collapsible. This means that smaller supply vessels can be used to transport and deliver it, which will produce a considerable saving on cost.

Less bulky and unwieldy than existing industry solutions, NAPS will be easier and quicker to install and operate and because time equals money, again the cost-savings are significant.

In addition, the modular ring construction offers an adaptable tool and the ability to replace only those parts that are damaged. Finally, but most importantly of all, it achieves its primary objective of reducing, by a significant and measurable quantity, the amount of damaging noise that is released by undersea piling and drilling.