Simrad ES60
(CD17004P)
BAC
Boundary water layers:
(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
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 t o minimise the influence of the boundary layer.
Propeller noise
The propulsion propeller is the dominant noise source on most
fishing vessels, research vessels, m erchant vessels and pleasure
crafts. The noise is transmitted through the sea water. For
this reason, the transducer should be placed far away from the
propeller, which m eans on the fore part of the hull. Positions
outside the direct line of sight from the propeller are favourable.
On small vessels with short distances it is advised to mount the
transducer on that side of the keel w here the propeller blades
move upwards, because the propeller cavitation is strongest on
the other side. The cavitation starts most easily when the water
flows in the same direction as the propeller blade, and that is to
some degree the case at that side of the keel where the propeller
blades move downwards.
Bow thruster propellers are extremely noisy. W hen in operation,
the noise and cavitation bubbles make the echo sounder useless,
almost no matter where the transducer is installed. And when not
in operation, the tunnel creates turbulence, and if the vessel is
pitching, the tunnel may be filled with air or aerated water in the
112
304699/A
To Next Page
Loading...
