Oceans of noise - Whale and Dolphin Conservation Society

Wind, Waves
& Currents
Hydrodynamic noise
Propulsion machinery
e.g. engines, motors, gears
(1) Turbulence
(2) Resonance
(3) Cavitation
Machinery noise
(1) Rotation
(2) Repetitive discontinuities
(3) Reciprocation
(4) Turbulence
(5) Friction
Vibration
(1) Rapid expansion & collapse
(2) Hammering
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Auxiliary machinery
e.g. generators, pumps,
air conditioning units
Seismic surveys Pile driving
(1) Cavitation
(2) Resonant excitation
of the hull
Propeller noise
Impulsive noise
Figure 3.1. Sources and causes of underwater noise associated with the oil and gas industries
3.4.1.1 Machinery noise
Propeller
Underwater machinery noise is the result of mechanical vibration that is coupled to the sea via,
for example, a ship hull, oil platform legs or through the ground. Within the machinery noise
class, a distinction between propulsion machinery (diesel engines, thrusters, main motors and
reduction gears) and auxiliary machinery (generators, pumps and air-conditioning equipment) can
be made. Causes of machine vibration are:
Unbalanced rotating shafts
Repetitive discontinuities, e.g. gear teeth, armature slots or turbine blades
Reciprocating parts e.g. combustion in engine cylinders
Cavitation and turbulence in fluids flowing through pipes, pumps, valves, condensers
Mechanical friction
3.4.1.2 Propeller noise
Propeller noise is distinguished from machinery noise in that it is the result of propeller action
and originates on the surface of the propeller. As the propeller rotates through the water, regions
of low or negative pressure are created at its tips, if and when these negative pressures become
sufficiently strong, bubbles (cavities) begin to form. These bubbles are short lived and collapse in
either a turbulent stream or against the surface of the propeller. A sharp pulse of sound is