Wake equalizing devices and vortex generators can have a stabilizing effect on propeller cavitation noise. Air
injection techniques show a large effect on the radiated noise level, even at low flow rates, in studies in the
cavitation tunnel. Using a variable instead of a constant RPM control schedule can be a very efficient measure to
mitigate the underwater radiated noise of controllable pitch propellers that operate at reduced power. Furthermore
this also can give significant advantages in reducing the fuel consumption.
Engine measures to reduce the underwater radiated noise differ per ship as the engine vibrations and noise are
sensitive to specific design. Specific measures have been studied in SONIC D3.4 by Pestelli (2016). For the cases
studied it was shown that a reduction of the engine speed reduces the combustion noise. It was furthermore shown
that for this case the more rigid mount and a more rigid and wider spaced foundation have a positive effect on
lowering the radiated noise. These mitigation measures are limited by the required propeller rotation rate, the
seaway regulations for the mounts and the strength requirement for the foundation.