Simrad EQ60 - Manual (Page 199)

Transducer installation
187
857-164342 / Rev.C
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.
The tarnsducer can be mounted inside the hull. A substantial
loss must be expected when the sound passes through the hull.
→ Refer to figure 29.
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.
Figure 29 Transducer mounting inside the hull
Stuffing tube
Transducer
(CD3001)
Air outlet Hole for oil filling
Oil