Simrad ES38-12 - REV C, Installation Manual, Page: 10 / 46

Simrad ES38-12
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.
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 and flat bottom, with a rising angle less
than around 13 degrees, is prone to giving air problems for the transducer. In any case a
transducer location in the forward part of the hull is preferred in order to minimise the
influence of the boundary layer.
Figure 1 Boundary water layer
A Turbulent flow
B
Laminar flow
C
Air bubbles in the water
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