Distance and Speed on the water

Distance on water is measured in nautical miles, and a nautical mile is about 15% longer than a mile. Why the difference? A mile on land equals 5280 feet, while a nautical mile equals one minute of latitude¹. It varies from 6046 feet on the equator to 6092 feet at a latitude of 60°. Therefore, 10 nautical miles equals about 11.5 miles on land.

Speed on water is measured in knots.  One knot equals one nautical mile per hour, or roughly 1.15 MPH. Perception’s cruising speed is typically 7.5 knots, which converts to about 8.6 MPH. (We travel a little slower than your average skateboarder!)

The term knot dates from the 17th century, when sailors measured the speed of their ship using a device called a “common log.” The common log was a rope with knots at regular intervals, attached to a piece of wood shaped like a slice of pie. Mariners would lower the wood piece into the water and allow it to float freely behind the ship for a specific amount of time (often measured with an hourglass). When the time was up, they would count the knots between the ship and the piece of wood, and that number estimated their speed.¹

Measuring the knot in the 17th century. ¹

1 _{NOAA. What is the difference between a nautical mile and a knot? National Ocean Service website, https://oceanservice.noaa.gov/facts/nautical-mile-knot.html. 01/20/2023}

(Melinda)