Log Line

A measured line with a drag device used to determine a vessel’s speed through the water.

In the traditional chip log, a sector-shaped board was streamed astern while the line paid out. Knots spaced at calibrated intervals were counted during a timed period, giving speed directly in knots.

The reading was speed through the water, not speed over the ground, and was affected by timing, line calibration, sea conditions and handling. Modern mechanical and electronic logs use different sensing methods but preserve the name.