Did crosswinds interfere with knot (speed) calculations before the chronometer?


I remember reading that crosswinds interfered with knot (speed) calculations before the chronometer in 18th century sailing. I’m not sure if I remember correctly. Can anyone confirm if this was the case and how these winds would have dine so. If it wasn’t crosswinds what weather phenomena would have done so?

I look forward to your feedback.

Navigation pre-accurate chronometer was pretty hit and miss. Lattitude was easy enough using the sun and the Polar Star. Longitude was always the problem and without being able to tell the time accurately, navigators could only guess how far East or West they were.

The actual speed calculation, in the sense of speed through the water, was made by dropping a weight attached to a string over the side. The string had knots ever fathom (6 feet) and by counting the knots as the line ran out, timed with a sandglass it was trivial to calculate speed.

Navigators knew that if they set off from Egypt and headed North, they would bump into Italy sooner or later. Later on, they knew that if they set off from Portugal and headed East they would bump into S America, probably Brazil, eventually.


You know, solar system east.

Or a brain fart.

Hey, it worked for Columbus!

He headed west. It’s in the song.

As bob++ says, latitude wasn’t hard, but longitude was really hard. So navigation included an element of dead reckoning. How fast are you going and what direction? How fast, well you use a log (string with knot tied in it) and a timer. What direction? A compass.

Trouble is, boats don’t actually go the direction they are pointed. (This is the difference between your course and your bearing.) Currents are one problem, but also sailing boats only go where they are pointed if the wind is dead astern. Any other wind angle and they have some sideways motion (leeway) as well. Estimating your leeway is non-trivial. Sailing with the wind at a difficult angle could thus make navigation much more error prone. Sailing ships of traditional design have pretty poor lateral resistance, and may have significant leeway.