Kongsberg EM 712, Installation Manual

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401027/B
Keep the transducer far away from the propellers
The propulsion propellers is the dominant noise source on most vessels. The noise
is easily transmitted through the water. This noise may often reduce the overall
performance of your EM 712.
The transducer must be installed as far away from the propellers as possible. The best
positions are therefore on the fore part of the hull. Positions outside the direct line of
sight from the propellers are best.
On small vessels we recommend mounting the transducer on that side of the keel where
the propeller blades move
upwards . This is because the propeller cavitation is weakest
on that side. The cavitation starts when the water flows in the same direction as the
propeller blades. This is where the propeller blades move downwards.
Choose a transducer position far away from the bow
thruster(s)
Bow thruster propellers are extremely noisy. When you decide where to place the
transducer, you must consider the noise created by most bow thrusters.
When in operation, the noise and cavitation bubbles created by the thruster may make
your EM 712 Multibeam echo sounder useless, almost no matter where the transducer is
installed. When the bow thrusters are
not in operation, the tunnel creates turbulence. If
your vessel is pitching, the tunnel may be filled with air or aerated water in the upper
position and release this in the lower position.
In general, the transducer should therefore be placed well away from the bow thruster(s).
However, this is not an invariable rule. Certain thruster designs - combined with their
physical locations on the hull - may still offer a suitable location for the transducer, even
close to the thruster. If you are in doubt, consult a naval architect.
Summary and general recommendations
Some of the installation guidelines provided for transducer location may be conflicting.
For this reason, each vessel must be treated individually in order to find the best
compromise.
In general, the most important factor is to avoid air bubbles in front of the transducer
face. For this reason, the recommended transducer location is normally in the fore part of
the hull, well ahead of the noise created by the bow wave.
The maximum distance from the bow is normally equal to one third of the total water
line length of the hull.
If the vessel hull has a bulbous bow, this may well be a good transducer location, but
also in this case the flow pattern of the aerated water must be taken into consideration.
The foremost part of the bulb is often a good location.
This applies to the vessel in normal trim and speed.
Kongsberg EM 712 Installation manual