Speedo Calibration
14 September 2024 · 12 min · 2K views · Chester River
What this video covers
Calibrating a boat’s speed and distance instrument requires measuring the difference between the speed through the water, indicated by the hull-mounted spinner, and the speed over ground.0:56 To perform this, select a measured course of at least 0.5 nautical miles between two fixed objects, such as pilings or range markers, oriented perpendicular to the current.1:30 Motor at a constant engine speed in both directions over the course, recording the elapsed time and the indicated water speed for each leg.2:42 Calculate the speed over ground for each direction by dividing the chart-measured distance by the elapsed time.2:50 Determine the speed correction factor by dividing the speed over ground by the indicated speed, then average the results from both legs.2:56 This correction factor applies to both speed and distance measurements.3:21 During five tests on the Island Packet 40 *Navigator* in the Chester River, this method yielded consistent correction factors between 0.85 and 0.88.11:54 Applying these factors improves the accuracy of dead reckoning, running fixes, and estimated time of arrival calculations.12:19
Boats in this video
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