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THE ECHOTRAC E20 IN ACTION
External annotations of the echogram can be triggered via s7k protocol. For details, refer to the Data
Format Definition document (see Appendix A – Reference Documentation).
6.3
Interference Considerations
Physical limitations in the functionality of the system must be taken into consideration when installing
and operating echosounders, including the Echotrac E20. Some of the limitations are absolutes;
others can be overcome to some degree. The following subsections provide examples of different
kinds of limitations.
6.3.1
Cavitation
Some reduction in the transmitted source level is expected to be caused by cavitation.
Propeller Cavitation
Propeller cavitation can be a significant concern for two reasons. First, the frequency of propeller
cavitation noise is in the operating frequency band of most echosounder equipment. Second, the
source levels of the propellers installed are expected to be high unless special quieting techniques
have been implemented.
Propeller energy typically propagates to the forward area of the echosounder equipment via a direct
or hull-grazing path. The other arrival path of propeller energy is by the bottom bounce path. This path
will be more significant in shallow water depths (less than 500 meters). The potential impact can be
further quantified for particular bottom depths of proposed operational test sites.
Appendage Cavitation
Appendage cavitation can result from rough or unfaired edges on the hull and can even be present at
lower speeds. If the source is located near the acoustic sensor installation area, it can be a significant
noise deficiency. It is difficult to predict the occurrence of appendage cavitation without under-hull
drawings, pictures, or visual inspection of the ship when in dry-dock.
6.3.2
Machinery Noise
Machinery noise should not be a major factor for acoustic sensors that operate at frequencies above
5kHz. Mechanical machinery noise is usually prevalent at 2kHz and below, though it is occasionally
detected at higher frequencies when fluid flow through pipes or cavitating pumps are involved.
Typically, the most important consideration for machinery noise is the proximity of the acoustic sensor
to the machinery source. There has been one observed case where diesel engine piston frequency
harmonics have been the controlling noise source at 12kHz, but in this situation, the engine room and
the acoustic sensor compartment shared a common bulkhead. Normally, acoustic devices are
sufficiently distanced from major machinery noise sources that machinery noise does not interfere.
A concern remains that there may be some auxiliary machinery (or other unusual equipment) located
near the acoustic sensor that could produce noise interference. An inspection of the installation site
and ship drawings to verify the position and proximity of all shipboard equipment should be conducted
to determine if there is a potential for machinery interference prior to conducting at-sea testing.
6.3.3
Electrical Noise
Due to measures in the electrical design of the echosounder, it is very robust and insensitive to
electrical noise. However, in the event of noise, please consider the following basic advice:
o
Avoid low budget DC to AC power converters and power generators.
o
If necessary, use stabilized UPS as a power buffer for AC supply, or use a straightforward DC
supply via a dedicated battery pack.
Echotrac E20 Operator's Manual8
Version 8
p. 35 of 60
Uncontrolled Technology Subject to Restrictions Contained on the Cover Page.
November 25, 2020
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