Furuno FR-7041R-MARK-2 Operator's Manual page 17

1. OPERATION
The [A/C SEA] control reduces the amplification of echoes at short ranges (where
clutter is the greatest) and progressively increases amplification as the range
increases, so amplification will be normal at those ranges where there is no sea
clutter.
The proper setting of the [A/C SEA] control should be such that the clutter is
broken up into small dots, and small targets become distinguishable.
If the A/C SEA is too low, targets will be hidden in the clutter, while if it is set too
high, both sea clutter and targets will disappear from the display. In most cases
adjust the control until clutter has disappeared to leeward, but a little is still visible
windward.
1. Confirm that the sensitivity is properly adjusted, and then transmit on short
range.
2. Adjust the [A/C SEA] control so small targets are distinguishable but some
clutter remains on the display.
Tip for adjustment the A/C SEA
A common mistake is to over-adjust the circuit so all the clutter is removed. As an
example set up for maximum A/C SEA. You will see how the center of the display
becomes dark. This dark zone can be dangerous (targets may be missed),
especially if the sensitivity is not properly adjusted. Always leave a little clutter
visible on the display to be sure weak echoes will not be suppressed. If there is
no clutter visible on the display, turn off the circuit.
A/C SEA may erase weak echoes.
1-8
Sea clutter at
display center
Figure 1-7 Sea clutter
CAUTION
A/C SEA control adjusted;
sea clutter suppressed