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Simrad ES38B
Figure 8 Acoustic window
Steel tank
A
Oil
B
Acoustic
C
window
Cable service
D
loop
E
Stuffing tube
F
Cable in steel
conduit
G
Oil inlet
Transducer mounted inside the hull
18
Example: Acoustic window
The transducer shown in the figure below is mounted inside the
tank behind a strong acoustic window which could be made of
polycarbonate.
The tank is filled with oil.
The transducer can also be mounted inside the hull.
An installation of the transducer inside the hull, and sounding
through the hull, requires a good acoustic contact between the
transducer face and the hull. Build a tank around the transducer
and fill it with a liquid. Oil used in hydraulic systems is a well
suited liquid for this purpose. It contains no gas bubbles and
is non-corrosive.
Typical values of the two way loss are 3 dB for polyester, 6 dB
for aluminium and 10 dB for steel. Hulls made of wood or a
sandwich type with foam in the middle, attenuate the sound so
much that through hull sounding must be regarded as impossible.
The loss varies with the distance between transducer face and
the hull. The best result is obtained when the distance is half a
wavelength. Consult Simrad for advice. In addition to the loss,
the beam pattern is degraded, because a larger area of the hull is
set into vibrations.
338462/B
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