Marine navigation

Marine navigation is the art and science of steering a ship from a starting point (sailing) to a destination, efficiently and responsibly. It is an art because of the skill that the navigator must have to avoid the dangers of navigation, and it is a science because it is based on physical, mathematical, oceanographic, cartographic, astronomical, and other knowledge.

Marine navigation can be surface or submarine.

Etymology
Navigation (from the Latin word navigatio) is the act of sailing or voyaging. Nautical (from Latin nautĭca, and this from Greek ναυτική [τέχνη] nautikḗ [téjne] "[art of] sailing" and from ναύτης nautes "sailor") is that pertaining to navigation and the science and art of sailing. Naval (from the Latin adjective navalis) is that relating to ships and navigation, or particularly to the navy.

In Ancient Rome, the navicularii conducted long-distance trade by sea.

History
Coastal navigation was practiced since the most ancient times. The biblical account of the great flood, where the Noah's Ark appears, is based both on myths and on the navigational practice of the Mesopotamian civilizations, who from the Sumerians onwards navigated their two rivers (Tigris and Euphrates) and the Persian Gulf. The ancient Egyptians did not limit themselves to inland navigation of the Nile either, and used the Mediterranean sea routes existing since the Neolithic — through which cultural phenomena such as megalithism or the metallurgy would have spread for millennia. The Cretans even established a true thalassocracy (government of the seas, attributed to King Minos) until the Mycenaean period (2nd millennium BC), when the events mythologized in the Homeric poems ought to be placed.The Hittites, led by King Šuppiluliuma II faced the Cyprus in the first historically recorded naval battle (ca. 1210 BC); at the same time, all the civilizations of the Eastern Mediterranean suffered from the incursions of the denominated "Sea Peoples".

The Phoenicians — whom the Greeks considered their masters in navigation and who are also cited in the Bible — would have been the first Mediterranean civilization to sail the high seas by sculling and sailing, guided by the sun during the day and by the North Star at night. It is recorded that, crossing the Strait of Gibraltar — the "Rock of Gibraltar", the so-called "Pillars of Hercules" in the Greek myths — they sailed across the Atlantic Ocean reaching the south to some point on the west coast of Africa and the north to the British Isles (or even beyond, to the place that the texts call Thule), but it is unclear if they circumnavigated Africa or crossed the Atlantic reaching America, something most likely achieved by the Norsemen in the 10th century.

Methods and techniques
These are the methods used in maritime navigation to solve the three problems of the navigator:


 * Determining and maintaining the "course".


 * Determining the "time", the "speed" and "distance", for the duration of the voyage.


 * Knowing the "depth" in which one is sailing so as not to run aground.

Coastal navigation
Navigation and location of the ship by positioning techniques based on the observation of bearings and distances to notable points on the coast (lighthouses, capes, buoys, etc.) by visual means (pelorus), observation of horizontal angles (sextant) or electronic methods (bearings from radar to racons, transponders, etc.)

Dead reckoning navigation
Navigation and location of the ship by analytical means, after considering the following elements: initial location, bearing(s) — whether absolute bearings, surface bearings, or relative bearings. Also velocity as well as the external factors that have influenced the course either partially or entirely, such as the wind (leeway) and/or the current (bearing of the current and hourly current intensity). The point obtained from the calculations is called the "Dead reckoning location", with its corresponding latitude and longitude. This point is also known as Fantasy point.

Loxodromic navigation


Navigation that follows a rhumb line — that is, all meridians are cut at the same angle. On a nautical chart following the Mercator projection, a loxodromic is represented by a straight line.

This type of navigation is useful for not too long distances, as it allows the course to remain steady, but it does not offer the shortest distance.

Orthodromic navigation
Navigation that follows the shortest distance between two points, i.e., that which follows a great circle. Such routes yield the shortest distance between two points on the globe. To calculate the bearing and distance between two points it is necessary to solve a spherical triangle whose vertices are the origin, the destination, and the pole.

Celestial navigation
Navigation and location of the ship by geopositioning techniques based on the observation of the stars and other celestial bodies. The variables measured to find the location are: the observed angular height of the stars above the horizon, measured with the sextant (formerly with the astrolabe or other instrument), and the time, measured with the chronometer.

Conceptually, the process is not complex to understand:


 * Knowing the time of the observation, and with the data contained in the nautical calendar, it is possible to determine the astronomical coordinates of the observed star.


 * Knowing the coordinates of the observed star and the height above the horizon with which it was observed, we can deduce that the observer's position is located on a circle whose center is located at the geographical point directly below the star.


 * Any observer located at any point on that circle will observe the star with the same height above the horizon.


 * The observer can therefore know that his position is somewhere on this circle.

In practice, the mathematical process, called "reduction" of the observation, can be complex for the uninitiated. To the height observed with the sextant, it is necessary to apply a series of corrections to compensate for atmospheric refraction, parallax and other errors. Once this is done, it is necessary to solve a spherical triangle by mathematical and trigonometric methods.

There are many methods to do this. The manual methods use tables (trigonometric, logarithms, etc.) to facilitate the calculations. The introduction of calculators and electronic computers at the end of the 20th century greatly facilitated the calculation, but the creation of GPS made celestial navigation no longer important, relegating it to the background as an alternative method in case of failure of the on-board electronics or as a hobby of scientific interest.

Electronic navigation
Navigation and location of the ship by positioning techniques based on the aids provided by global positioning systems, such as GPS, GLONASS, or GALILEO. It is the system most widely spread and easiest to use, in spite of the errors that may arise.

Inertial navigation
Navigation and location of the ship by means of the analysis of the data provided by accelerometers and/or gyroscopes located on board, which integrate the accelerations experienced in complex electronic systems, that converted into velocities (in the 3 possible axes of displacement) and according to the observed courses, make it possible to obtain the location of the ship.

Iconography
The harbinger of a successful navigation was the dolphin, which is why its representation became the symbol carried by all ships.

More recently, navigation was represented as a woman crowned with ship's sterns whose clothes are agitated by the winds. She rests one hand on a rudder and the other holds the instrument for measuring height. At her feet, the ampoule, the compass, the trident of Neptune and the riches of commerce, while the sea can be seen on the horizon, completed by a lighthouse and traversed by ships at full sail.