8.1 Consideration should be given to the selection
of onboard machinery along with appropriate vibration control measures,
proper location of equipment in the hull, and optimization of foundation
structures that may contribute to reducing underwater radiated and
onboard noise affecting passengers and crew.
8.2 Designers, shipowners and shipbuilders should
request that manufacturers supply information on the airborne sound
levels and vibration produced by their machinery to allow analysis
by methods described in section 5.2 and recommend methods of installation
that may help reduce underwater noise.
8.3 Diesel-electric propulsion has been identified
as an effective propulsion-train configuration option for reducing
underwater noise. In some cases, the adoption of a diesel-electric
system should be considered as it may facilitate effective vibration
isolation of the diesel generators which is not usually possible with
large direct drive configurations. The use of high-quality electric
motors may also help to reduce vibration being induced into the hull.
8.4 The most common means of propulsion on board
ships is the diesel engine. The large two-stroke engines used for
most ships' main propulsion are not suitable for consideration of
resilient mounting. However, for suitable four-stroke engines, flexible
couplings and resilient mountings should be considered, and where
appropriate, may significantly reduce underwater noise levels. Four-stroke
engines are often used in combination with a gear box and controllable
pitch propeller. For effective noise reduction, consideration should
be given to mounting engines on resilient mounts, possibly with some
form of elastic coupling between the engine and the gear box. Vibration
isolators are more readily used for mounting of diesel generators
to foundations.
8.5 Consideration should be given for the appropriate
use of vibration isolation mounts as well as improved dynamic balancing
for reciprocating machinery such as refrigeration plants, air compressors,
and pumps. Vibration isolation of other items and equipment such as
hydraulics, electrical pumps, piping, large fans, vent and AC ducting
may be beneficial for some applications, particularly as a mitigating
measure where more direct techniques are not appropriate for the specific
application under consideration.