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very efficiently transmitted through the generally stiff, metallic and therefore resonant
structures. One common way of overcoming the considerable nuisance this can cause for the
occupants is by absorbing the vibration and actually converting it to heat using
viscoelastic polymer materials, typically based on polyurethanes or acrylics. 
Over the past 20 years, Swedish Acoustic Products -- Swedac -- has built a track record
in overcoming noise and vibration problems using this basic technology. Goran Falk, the
company's technical director, claims it is possible to reduce noise levels by 50-70% with
the right choice of materials and their effective application. 
Although we have a range of standard products, the skill comes in knowing how best to use
them. One also has to keep an open mind about modifying existing products or designing
completely new solutions when the conditions require it, he says. Falk believes that
sound and vibration suppression should be an integral element of the design of the
structure as a whole and not an 'add-on'. For this reason, Swedac offers sound-damping
engineering consultancy to ship and offshore platform designers and builders. 
The company has supplied over 200,000 m2 of sound-damping deck coverings over the past 15
years. These generally consist of a trowel-applied liquid polymer, which, when dry, is
overlaid with an SBR latex concrete. If speed of application is an issue, the
liquid-applied polymer can be replaced with an adhesively-bonded polymer sheet. 
Where the requirements are more stringent, for example, in laboratory areas, the company
can offer a 'floating floor'. This comprises proprietary sound-damping PVP
(plate/viscoelastic polymer/plate) laminate plates laid on top of 50mm of mineral wool
(140-150 Kg/m3). The sound-damping plates, which were conceived by Swedac, consist of two
layers of steel or aluminium, each 2 or 3 mm thick, separated by a thin layer of
viscoelastic polymer. 
While the performance of this type of system is impressive, even better sound and
vibration suppression can be achieved, particularly at the lower frequencies commonly
produced by engines, propellers, mud pumps and so on, by combining the floating floor
with the company's standard viscoelastic polymer plus SBR latex concrete system (Figure
1). The measured insertion loss, ILv, expressed in dB for this system over a range of
frequencies is shown in Figure 2. 
Emtunga modules 
Swedac has developed similar but thinner (2 mm total) and lighter PVP laminate plates for
attaching to bulkheads to reduce noise transmission between cabins. Emtunga has used
these extensively in the construction of accommodation modules. 
In another variation on this theme, Swedac has supplied single steel sheets to Kvaerner
with a layer of viscoelastic polymer that can be easily bonded to an existing steel
surface. Kvaerner regularly uses this product on the plinths supporting water injection
pumps on offshore platforms. 
Recognizing that noise and vibration problems may only manifest themselves when
structures have been completed and that older vessels may need to be upgraded, Swedac has
also developed a cassette damping system for retro-fitting to bulkheads, vessel sides and
beneath floors -- essentially anywhere in the noise path -- within ships and offshore
platforms. These are simply a narrow steel trough containing viscoelastic polymer into
which has been set a series of steel lugs to allow welding to the structure. 
Swedac supplied its products and services widely in the offshore sector during the 1990s
but suffered, like most suppliers, from the downturn towards the end of the decade. It
switched its attention to the cruise ship market where it has