Echo Sounders and Speed Logs

An echo sounder times a pulse to the seabed and back. The displayed value may be configured as depth below the transducer, below the keel or below the waterline. Record the transducer position and any offset before comparing the reading with charted depth plus height of tide. The charted sounding, tide estimate and sounder may also use different reference levels.

Aeration, heel, weed, soft mud, a steep seabed, transducer installation and inappropriate gain or range can degrade the return. A shallow-water alarm is a warning layer, not evidence that water is safe until it sounds. Compare trend and expected profile, retain margin and act on an unexplained discrepancy.

A yacht log commonly measures speed through water. Fouling, turbulence, heel and calibration affect it. GNSS SOG measures movement over the seabed and includes current. The difference can help expose set and drift, but only after heading, leeway, instrument health and time basis are checked.