Since we left behind Golfo de Coronados with its many whales, the winds had eased down. Light airs and a long low swell made for a bit of rolling as the Europa motors her way North. 

Sails are hanging on their gear ready to be set whenever there’s a good puff of wind. We had to wait until late at night for the breeze to slightly increase. Braced square and sailing downwind, the engines are turned off for a while, but still some speed is needed for the remaining miles to cover and the limited time we have. A couple of hours later the engines push again, though now with the help of some of the square sails. Early morning saw a shift in the gentle wind backing from South to Southeast. Hands were called on deck again, the braces are pulled and courses clewed up. 

It seems that these conditions and the way of dealing with them will be the trend for the next couple of days as we sail to Talcahuano.  

Calm and sunny as it was today, it gave us the chance to relax and spend time on deck. Not much sail handling was to be done, engines are on and voyage-crew watches have been kept on standby since yesterday evening. It is warm and the sun shines over the horizon… wait a minute, sun and horizon… the two bases for a bit of introduction to Celestial Navigation.  

For a while, Sextants came out of their boxes and were handed to the ones interested in being acquainted with them. 

Accurate timekeeping, complex calculations, and data extracted from the yearly Almanac follow the taking of the “sights” with the sextant. 

It all starts with “taking a sight” using the sextant as the means to know the angle of the celestial body (most commonly the sun but also are usable the moon and many stars) from the horizon at a given time. The idea is to ultimately get to know the angle between the celestial body and where its zenith (highest point in the sky) projection hits the center of the earth. 

So, besides this amazing piece of mechanical genius, a good time timepiece is required too, and a current Almanac with the schedules of the coordinates of celestial objects over the planet’s surface, plus a set of sight reduction tables and a chart of the region. 

A complicated method that starts with the romanticized idea of the use of classical old instruments like the sextant, just to hit a wall afterwards when realizing the loads of calculations to make, to actually achieve a position in the chart. 

An elaborate method that was used until the discovery of new technologies, like the satellite positioning so extended nowadays in all kinds of gadgets. Used as we are nowadays at just having a look at our wristwatch, phone or sitting at the wheelhouse surrounded by screens of all kinds giving us directly our exact location on earth, it is hard to imagine how for centuries navigators have been venturing into the vast expanse of the limitless ocean without them. Navigators had to know and use those time-consuming, difficult methods and thorough calculations every time a position was needed. 

Something similar, but much less of a complex procedure, happens when we want to know our speed. The bridge instruments give us directly a number, how fast or how slow we are moving in the ocean in a determined direction. But to figure out the speed of the ship in the classic times of sailing, things were different too. 

At the beginning, the method was basically to throw a floating object overboard and use a sandglass to measure the time it took to pass between two points on deck. But the technique evolved to the use of the so-called Chip-Log, which we also have on board for using and showing the method in days like today.  

The device consists of a weighted wooden panel with a determined shape and size, attached by a long line to a reel.  

This rope has knots tied at equal intervals proportional to the nautical mile and to the time interval used for measurement. The use of the nautical mile as standardized measure began in the 15th century, and is defined as the meridian arc length corresponding to one minute (1/60 of a degree) of latitude, 1852 meters. 

The line is allowed to run free at the stern of the ship while a sailor counts the knots that pass through his hand, tied every 14.4 meters and for 28 seconds. 

Why this space between knots and this timing? 

1kn is the speed measure of a nautical mile per hour, or 1852 m/h, which in seconds is 0.5144 m/s.  

Traditionally the spacing between knots was agreed at 8 fathoms.  

1 fathom is equal to 1.8288m, so that gives us a spacing between knots of 14.4 meters  

At 1 mile per hour (or 0.5144 m/s) then it would take 28 seconds to cover this 14.4 meters  

The device we practice with today is very similar to the classical one but it just uses half of this distance and time. 

Until the mid-19th century, this was the way for measuring the vessel speed through the water. To this day, sailors still indicate speed in knots.