EQ-55 Operators Manual
950-70017001/Iss 1.2
Installation Instructions for the EQ-55
Page 4.11
Kongsberg Simrad Mesotech Ltd.
Port Coquitlam, BC - Canada
4.3
DETERMINING THE POSITION FOR THE TRANSDUCER
4.3.1
General
A single answer to the question where to locate the transducer cannot be given.
It depends very much on the vessel’s construction. However, there are some
important guide lines.
4.3.2
Go Deep
The upper water layers of the sea contain myriads of small air bubbles created
by the breaking waves. In heavy seas the uppermost 5-10 metres may be air-
filled, with the highest concentrations near the surface. Air bubbles absorb and
reflect the sound energy, and may in the worst cases block the sound
transmission totally. Therefore, mount the transducer at a deep position on the
hull.
Consider the situation when the vessel is unloaded, and when it is pitching in
heavy seas. The transducer must never be lifted free of the water surface. Not
only will the sound transmission be blocked, but the transducer may be
damaged by slamming against the sea surface.
Another reason to go deep is cavitation in front of high power transducers.
Cavitation is the formation of small bubbles in the water due to the resulting
local pressure becoming negative during parts of the acoustic pressure cycles.
The cavitation threshold increases with the hydrostatic pressure.
4.3.3
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. Figure 4.1
sketches the boundary layer of a vessel moving through the water.
Furthermore, air bubbles in the sea water are pressed down below the hull and
Summary of Contents for EQ 55
Page 1: ...EQ 55 OPERATORS MANUAL 950 70017001 Issue 1 2 February 1998...
Page 2: ......
Page 4: ......
