Log Reading

The distance or speed value indicated by a vessel’s log instrument at a recorded time.

A cumulative distance-log reading is entered in the navigation record at regular intervals and compared with the previous reading to find distance run through the water. Some instruments also display instantaneous speed through the water.

The reading is affected by calibration, fouling, sensor position and water flow and is not the same as GNSS distance or speed over the ground. Recording the time, value and units consistently allows later checks and supports dead reckoning.