Tecnoseal Answers - Maritime Navigation Methods
It was from this year February, precisely from the article dedicated to the equipotential bonds (which you find here) that we were not dealing with a topic in the nautical physics category. An absence that we solve with today's Tecnoseal Answers where we will talk about maritime navigation and the various typologies in which it is divided.
Before we start, I remind you that at the following link you can find a thematic index of all the Tecnoseal Answers released until today.
a prestigious vintage marine chronometer
Some Short History
With the term maritime navigation we refer to that set of techniques used to determine the position and course of a ship at sea so that it can be moved from point A (departure ) to a point B (destination), in maximum security and economy. These last needs mean that the route chosen does not always correspond to the shorter one. The maritime navigation was one of the first inventions of man and has existed since ancient times. Traditionally it was based on the observation of reference points whose position was known (above all sun, moon, stars) to determine the geographic coordinates of the observer's position.
Subsequently this observation will be made more efficient through the introduction of numerous instruments, such as the sextant (the latter seems to have been invented by the Egyptians even if the first recorded use is from 1731). A first maritime navigation revolution occurred in 1761 with the invention by the English watchmaker John Harrison of the marine chronometer which will allow, for the first time, to accurately determine the longitude on the high seas. The technological progress that has started since the 20th century has lastly allowed a second revolution in maritime navigation that can now be carried out using sensors capable of determining the position through the use of man-made points of references (satellites, WLAN repeaters, etc).
The Astronomical Navigation
From the historical background provided we can note that, technically, there are two different methods of performing maritime navigation. The most secure and ancient method for determining longitude is that of the astronomical navigation, formerly known as the "Lunar distance method." It is said that by using it, even Amerigo Vespucci, during one of his travels in the seas of the new world, succeeded with unexpected accuracy in determining the position of places on the Caribbean coast of Venezuela.
The astronomical navigation is therefore that type of navigation carried out with the aid of the visible celestial bodies (stars, planets, sun and moon). It is still used a lot today, despite the presence of the satellite methods mentioned above. It is a completely autonomous technique, it does not need any technological support (although the use of a sextant makes all measurements much simpler) and allows you to identify your position at sea (ship point) with incredible precision. It is therefore fundamental to navigate in the absence of optical references or alternative methodologies.
Some of the traditional tools used in estimated navigation
The Estimated Navigation
Although the estimated navigation was certainly not invented in 1761, it was only in that year, with the invention of the marine chronometer that it finally took hold, being able to be used with much more security than before. The problem, in fact, was all about constantly knowing the exact time so as to be able to determine, through numerous calculations, the longitude of one's boat. The invention of the London watchmaker turned out to be almost perfect, not only was it practical and light, but also allowed to have on board, with remarkable precision, the time of the Greenwich meridian on which to base one's calculations.
In any case, the estimated navigation is that technique by which it is possible to determine the estimated point, that is the estimated position of the ship at sea, using elements of motion, such as speed, direction and meaning. This position is always affected by measurement errors (given by the precision of the instruments) and evaluation mistakes (given by the difficulty of correctly evaluating and determining the effects produced by the wind, by the currents and by the state of the sea). This error averages about 1/20 of the path traveled and, therefore, increases with time. For this reason, a form of astronomical navigation is still used as "verification" of one's position.
Navigation Types by Position
The astronomical and estimated navigation are distinguished from the technical point of view, but within the boating one tend to distinguish the various typologies of maritime navigation also in base to the position of the ship. Let's look at these other types of maritime navigation:
- The offshore sailing is the main type of maritime navigation since it is the one that takes place in the open sea (over 20 nautical miles from the coast), in the complete absence of visible references. To implement it we use a mixture of estimated, astronomical and satellite navigation. We haven't talked about this last one in detail, but it's a mixed navigation which estimates its position based on the surveys of satellites in orbit. Although it is similar to astronomical navigation, it is also affected by a certain amount of error (even if smaller than that of the estimated one).
- The coastal navigation is the one that takes place near the coast (within 20 miles). This is managed using conspicuous points of the territory which can be observed with the naked eye or detected by compass/radar. Everything is completed with a series of surveys and distance measurements.
- Lastly, the piloting is the navigation phase in which the conspicuous points of the coast are too close and do not allow detection. The position of the ship is therefore determined directly on sight. The pilot has in fact the possibility to know in real time the situation within the harbor waters both regarding the movement of the ships and of particular temporary conditions failure of maritime light signaling systems. To these can also add the knowledge of local climatology and its effects on navigation so as to reduce the risk of the ship impacting obstacles. The presence of a pilot on board guarantees greater speed and safety for many precision maneuvers.
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