Chart Navigation & Plotting · Soundings
Running a line of soundings to check position, you compare charted depths to your echo sounder readings after correcting the sounder for:
- AVariation and deviation
- BThe transducer depth below the waterline and the height of tide✓ Correct
- CCompass error only
- DGreat-circle convergence
Explanation
To compare soundings with the chart, add the transducer's depth below the surface to the sounder reading to get depth below the waterline, then subtract the height of tide to reduce it to the chart datum (MLLW). The corrected soundings can then be matched to the charted contours.
Authority: Bowditch, American Practical Navigator (Pub. 9), piloting by soundings
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