Definition
A settable threshold on the echo sounder that sounds when displayed depth falls below or rises above preset values. The shallow alarm is normally set to the planned minimum safe depth, that is intended under keel clearance plus draught, referenced to whatever datum the display is calibrated to, and should be reset for each leg as the plan's margins change. A deep alarm is useful when following a contour or when anchored, warning that the vessel has dragged into deeper water off the selected bank.
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