Measuring Speed in Knots Started With Tying Knots in Rope
By Chad Upton | Editor
Sailors have it easy these days — an inexpensive GPS will tell you how fast your ship is travelling. Heck, even your smartphone can do it if you have the right app. That’s how I clocked the car ferry on Lake Michigan at 35 mph (56 km/h) last summer.
However, a blackberry could not measure your speed 450 years ago. That required a “chip log” (aka “ship log” or “log”). This was a spool of rope attached to a small piece of wood. The sailors would place the wood in the water where it would drag in the water, unspooling the knotted rope. One sailer count the knots passing over the haul and another would use a 30 second sandglass to measure the time. They had a table to lookup the speed (“knots”) based on the number of knots that passed by.
Although the method has changed significantly, the units are still called “knots.” To put that in a way that might have more meaning, one nautical mile translates to 1.151 miles or 1.852 km.
Photo: Rémi Kaupp (gnu license)