So you can navigate without tools and always know where you are


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Some time ago we told you the story of Italian-Brazilian Elio Somaschini (born in 1949 in Seregno, Brianza, Italy) and his voyage by sailboat (a First 40.7) around the world, from 2006 to 2013, without the use of navigational instruments.

Elio Somaschini

Instead of the sextant, the navigator (who was an entrepreneur but first and foremost a physics luminary) used his hand to measure the position of the stars.


We contacted him to have him explain in detail the technique he used. Empirical, but effective. With the “lesson” of Elio (and illustrations by Luna Poggi) we tell you how to calculate latitude and longitude using only your hand, eyes and a good watch. According to Somaschini it is easy, you can do it too.


Many of you will have seen “Oceania,” the Disney animated film: the young protagonist Vaiana, at one point, while sailing at night on her “proa” (the typical asymmetrical Polynesian multihull), points her hand to the sky like a sextant to calculate the boat’s latitude by taking advantage of the stars. Somaschini uses a very similar system, not coincidentally taught to him by a student of Micronesian navigation guru Mau Piailug (1932-2010).

Elio explains, “Stand and open your arms as if you were on a cross. Now turn your head toward the hand with which you wish to take the measurement and open your fingers wide, so that your little finger is downward and your thumb is upward. With one eye open, placing the tip of the little finger on the horizon line, the tip of the thumb will be about 23 degrees above. This value may change little from person to person, but roughly speaking we are there. it is useful to know that each finger, placed perpendicular to the outstretched arm is worth 2 degrees and the closed fist is worth 10 degrees. So you will understand the position of the stars or the sun.”

This system allowed Helium to navigate and reach the set destinations with a maximum error of a few tens of miles, almost negligible after a long crossing. A necessary condition for calculation is to know the time: astronomical navigation is based on the time of the zero meridian (Greenwich), which has become UT (universal time) time since 1948.


We come to the “spannometric” calculation of longitude.Again, a good clock, even a digital one, is of paramount importance. Here is the method used by Elio, which involves marking the position of the stars (Somaschini’s “physicist” nature comes out here): “The clock uses 24 hours as the measure of the day. The Earth doesn’t go around itself in 24 hours, though! It takes just over 23 hours and 56 minutes (the exact value is called the sidereal day). You may ask: but if the one spinning is the Earth, why the difference? Because as it turns on itself (rotational motion) it also moves a little further around the sun (translation).

So in order to make a complete turn, it has to make a turn plus a small angle! This angle is worth one degree! You’re getting the trick: the movement of 1° is equivalent to the movement made by any star in 4 minutes! If you look at the sky, for example at 11 p.m. on day X, know that if you do not move, you will find the same sky at 10:56 a.m. the next day, 10:52 a.m. two days later, and so on. Imagine the same scenario: you left on the first day with the boat, and after five days you lie on the deck and watch the zenith of the sky above you.

If you had not left, you would find the initial setup at 10:40 a.m. (-4 minutes x 5 days = -20 minutes). But looking at the stars, the same conjunction occurs at 11:10. What does it mean? In this case that you moved in a westerly direction and that the stars took 30 minutes to “reach” you: 30 minutes divided by 4 minutes is 7.5. That is, expressed in degrees, the distance you traveled westward.

If you know the longitude of your starting point, here you now know your current longitude. With your hand, as I explained, measure the latitude and, you want, knowing that one degree in the maximum circle is worth 60 nautical miles, take the 7.5 degrees and multiply it by 60: 450 miles traveled, if you were on the equator.

If you are navigating on the 30° latitude? The calculation to be done is cosine of 30 = √3/2 = 0.85. You will have sailed 450 X 0.85 = 380 miles, with an average speed of 3.16 knots (380 miles divided by 120 hours). What a drag, there was little wind!”


Find the full story of Elio Somaschini in the December 2019/January 2020 issue of the Journal of Sailing, on newsstands and digitally.



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