Maintenance and troubleshooting 29
3.5 DSM400 Thermocline Troubleshooting
Thermocline Troubleshooting
This section describes how to troubleshoot incorrect depth
readings caused by “thermoclines” in certain areas of water.
Thermocline Overview
In temperature terms, oceans can be thought of in different
layers; a mixed layer and a colder deep layer, separated by a
thermocline layer, where there is an abrupt change in
temperature. The thermocline attracts additional marine life and
small particles of debris, reducing the accuracy of fishfinder
sonars, as shown below:
This problem occurs when fishfinder sonars (including the
DSM400) interpret the thermocline as the bottom of the seabed,
returning an incorrect depth reading. To overcome this problem,
you must configure the DSM400 to operate in a different
frequency range, using your Raymarine Multi-Function Display.
This is described in the following procedures.
Using Low and High Frequencies
Before performing any of the procedures detailed on this page, it
is important to understand the difference between low and high
frequencies. The DSM400 features both low and high frequency
transducers, enabling you to view low or high frequencies (or
both) in the fishfinder display.
Low
frequencies (less than 100
Khz) scan a wide area and penetrate water well, and are
suitable for displaying a large area below your boat, or in deep
water.
High
frequencies (100 to 200 Khz) scan a narrow area but
produce more detail, especially at high boat speeds. High
frequencies are well-suited to shallow waters up to 1000 feet.
D11138_1
0
2000
1000
Depth (feet)
Mixed Layer
Thermocline
Deep Water
Temperature
(
(
(
(
(
(
Actual Depth
(2000 feet)
Depth Detected by
Sonar (1100 feet)
D11138_1
D11152_1
A thermocline looks like a
thick speckled band on the
display. The debris and
marine life found in the
thermocline cause the sonar
to mis-interpret it as the
bottom, giving inaccurate
depth readings.
Thermocline
The scale for this part of the
display is not relevant in
this particular example.
Zoomed Area
This is the actual bottom
depth (2289 ft).
Actual Bottom
The thermocline causes an
incorrect depth reading.
False Depth Reading
DSM400 Installation Guide.book Page 29 Tuesday, November 4, 2008 4:53 PM
www.busse-yachtshop.de | [email protected]