Simrad ES200-7C - REV E, Installation Manual

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Simrad ES200-7C
noise at certain frequencies. Do not place an echo sounder
transducer in the vicinity of such objects, and especially not
close behind them. For the same reason, it is very important
that the hull area around the transducer face is as smooth and
level as possible. Even traces of sealing compound, sharp edges,
protruding bolts or bolt holes without filling compound will
create noise.
Mount the transducer at the forward part of the
hull to minimise the effects from the boundary
water layer
When the vessel forces its way through the sea, the friction
between the hull and the water creates a boundary layer. The
thickness of the boundary layer depends upon vessel speed and
the roughness of the hull. Objects protruding from the hull, and
dents in the hull, disturb the flow and increase the thickness of
the boundary layer. The flow in this boundary layer may be
laminar or turbulent. A laminar flow is a nicely ordered, parallel
movement of the water. A turbulent flow has a disorderly pattern,
full of eddies. The boundary layer increases in thickness when the
flow goes from laminar to turbulent. The figure below illustrates
the boundary layer of a vessel moving through the water.
Figure 1 Boundary water layer
A
Turbulent flow
B Laminar flow
C Air bubbles in the water
Furthermore, air bubbles in the sea water are pressed down below
the hull and mixed into the boundary layer. The boundary layer
is thin underneath the forward part of the vessel, and increases in
thickness as it moves towards aft. If the sides of the hull are steep,
some of the air bubbles in the boundary layer may escape to the
sea surface along the vessel sides. It is our experience that a wide
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