Visual Aids
Clasification
The visual aids to navigation have been commonly used because they are addressed directly to the seaman's senses and they do not require any special equipment to be detected on board. The messages emitted by these signals can be identified easily. In addition, these messages allow the seamen to determine the current ship position just by inquiring the Derroreros books, the lighthouse books and the chart of that area.The visual aids to navigation can be classified into blind signals and light signals. The blind signals emit a message during the daytime; meanwhile, the light signals emit the same message during the night.
The daytime message consists of the colour, shape and limit mark of the signal. However, this message can be only recognised in short distance, just few meters. These distances mainly depend on the visual keenness, the contrast of the background where it is cast, the atmosphere transparency, etc. The information provided by this type of message is helpful for any type of navigation, but especially for the coastal navigation, coastal fishing or sports crafts.
The night messages are based on the light colour and speed; that is, light and dark phases are
emitted rhythmically. Although the scope of the light can be as desired, it depends on the
geographical scope determine by the Earth's curvature. The visual aids to navigation can be split
into many groups: lighthouses, buoys, lightships, sighting, port lights, etc.
The lighthouses are placed in significant coastal points and its light scope is very intensive. However, its operation during the daytime is not standardised.
The buoys can be placed inland (on fixed signposts) or in the sea. Its light scope is not so intensive as the scope of the lighthouses. They are usually located in channels or dangerous points close to navigable waters.
The port lights are placed on the haven dikes, on the sides of the quays or in the borders of dredging areas. They guide the seaman in the arrival to the port and in the departure.
The sighting draws secure routes to get to the port.
The lighthouses are placed in significant coastal points and its light scope is very intensive. However, its operation during the daytime is not standardised.
The buoys can be placed inland (on fixed signposts) or in the sea. Its light scope is not so intensive as the scope of the lighthouses. They are usually located in channels or dangerous points close to navigable waters.
The port lights are placed on the haven dikes, on the sides of the quays or in the borders of dredging areas. They guide the seaman in the arrival to the port and in the departure.
The sighting draws secure routes to get to the port.
History and development
The origins of the visual aids to navigation date back to the humans' first attempts to discover new commercial routes, going far a way from the coast in their vessels. In the daytime, the geographical unevenness oriented these men. However, at night, they needed to use the light emitted by bonfires burning in strategic coastal points in order to come back to the port. Since the rain or the wind extinguished these bonfires, they were protected with a kind of structure and, later, with reflecting surfaces to intensify the light and to be seen in larger distances. Although these aids to navigation were not too complex, they required that somebody was always maintaining the flame. Thus, the lighthouses started.The first stable construction of this aid to navigation that we know was placed in the island Faros in Alexandria. This town, founded by Alexander Magnus, had a natural port with a high level of traffic. That is why it was required to build a big tower in the entry in order to guide the seamen. This tower was the mythical Lighthouse of Alexandria, currently destroyed.
We do not have any references of this type of structures in the Pre-Rome age. Although it is
thought that the Colossus of Rodhes, located in the entry to the Rodhes port, could be a
lighthouse, there is no proof of it. The Rome Age left many examples of these constructions. For
example, in Italy, we can find the Ostia lighthouse in the port of Rome, built by the Imperator
Claudio, the Mesina lighthouse in Sicily or the Capri lighthouse, destroyed by an earthquake at the
end of Tiberio's reign. Moreover, in France, the most outstanding lighthouses from this age are
located in Bologna, Frejus or Marseille. Finally, the lighthouse in Dover (England) is another
example of this age.
After the fall of the Roman Empire, the trade was stopped and the countries were focused on the wars more than on the social and economic development. Few new lighthouses were built, except for the lighthouse in the island Cordouan, which is also the first one built in open sea. Morever, the existing lighthouses were destroyed.Since the 12th Century, the navigation in the Mediterranean Sea and in North Europe was reactivated. In order to guarantee the safety in the shipping routes, lighthouses were built. Thus, Scandinavia and Germany had the best-lit coast in Europe (15 lighthouses in 1600). The trade in the Mediterranean Sea also promoted the construction of many lighthouses. In addition, bonfires were placed on existing watchtowers such as Porto Pi in Mallorca.
After the fall of the Roman Empire, the trade was stopped and the countries were focused on the wars more than on the social and economic development. Few new lighthouses were built, except for the lighthouse in the island Cordouan, which is also the first one built in open sea. Morever, the existing lighthouses were destroyed.Since the 12th Century, the navigation in the Mediterranean Sea and in North Europe was reactivated. In order to guarantee the safety in the shipping routes, lighthouses were built. Thus, Scandinavia and Germany had the best-lit coast in Europe (15 lighthouses in 1600). The trade in the Mediterranean Sea also promoted the construction of many lighthouses. In addition, bonfires were placed on existing watchtowers such as Porto Pi in Mallorca.
Since the 18th Century the lighting systems were considerably improved. The commercial
relationships between the States and the naval traffic increased and hence, it was required to have
lights in the most outstanding ports and to signal the coast and the existing dangerous elements
with reefs.
In that period, England was the country with more lighthouses since it charged the vessels putting in at its ports and invested these funds in maintaining the existing lighthouses and building new ones with new technologies. In addition, the French coast and the American colonies had a good lighting system. However, the remaining European countries and other countries in the world had a very poor system.
In the second half of the 19th Century, new materials and energy sources promoted the construction of lighthouses. In Spain, the Comisión de Faros (Lighthouse Authority) was created in 1842 and the first Maritime Lighting Plan was approved in 1847. This plan was the origin of the most of the current Spanish lighthouses.
Along with the traditional stone lighthouse, new metallic lighthouses were built, which were lighter. Some examples are the lighthouses in the delta of Ebro, Buda, El Fangar and La Baña. Other lighthouses are also remarkable due to its size, such as Cabo de Palos that housed the Escuela de Toreros, Chipiona and Trafalgar.
In that period, England was the country with more lighthouses since it charged the vessels putting in at its ports and invested these funds in maintaining the existing lighthouses and building new ones with new technologies. In addition, the French coast and the American colonies had a good lighting system. However, the remaining European countries and other countries in the world had a very poor system.
In the second half of the 19th Century, new materials and energy sources promoted the construction of lighthouses. In Spain, the Comisión de Faros (Lighthouse Authority) was created in 1842 and the first Maritime Lighting Plan was approved in 1847. This plan was the origin of the most of the current Spanish lighthouses.
Along with the traditional stone lighthouse, new metallic lighthouses were built, which were lighter. Some examples are the lighthouses in the delta of Ebro, Buda, El Fangar and La Baña. Other lighthouses are also remarkable due to its size, such as Cabo de Palos that housed the Escuela de Toreros, Chipiona and Trafalgar.
Lighting systems
Until the end of the 18th Century, all the lighthouses had either wood or coal bonfires or wicks within tallow or oil. These aids to navigation produce little light and a lot of smoke. In addition, they involved the transportation of heavy loads of fuel. The flames were protected with glass lanterns, although they were well ventilated.One of the first technological developments was a lamp with a cylindrical cotton wick surrounded by a glass tube that permitted to adjust the oxygen and absorbed the oil by capillarity. The amount of light emitted was increased by putting several wicks in one lamp. However, this mechanism used vast quantities of fuel and hence, other types of cheaper oils began to be considered.
With the arrival of the petrol, the oil was no longer used, since the petrol had a higher lighting power. The burners were enhanced. Soon, incandescent burners were used; in these burners, the fuel made its ascent by a tube through draft air until the vaporizer it became steam. This steam went out through an injector and was burnt with the air.
Later, gaseous fuels were tested in spite of the transportation and handling risks. Afterwards,
acetylene began to be used; this material provided a very bright flame and was also, dissolved with
acetone, less dangerous. The Sweden Gustav Dalen invented a gas device with automatic ignition.
This aid to navigation was termed solar valve. Dalen was awarded with the Physics Nobel Prize in
1812. The solar valve was used in isolated lighthouses. In Spain, it was applied, at first time, to
Peña Horadada, buoy placed in the entry of the port of Santander.
The electrical power was fundamental in the lighthouses. After some test in markers, Villano was the first electrical lighthouse on the Spanish coast. This lighthouse was provided with an arch lamp. Finally, the current lamps appear (incandescence, halogens, etc) as well as renewable power resources to feed these lamps (photovoltaic, wind, etc).
The electrical power was fundamental in the lighthouses. After some test in markers, Villano was the first electrical lighthouse on the Spanish coast. This lighthouse was provided with an arch lamp. Finally, the current lamps appear (incandescence, halogens, etc) as well as renewable power resources to feed these lamps (photovoltaic, wind, etc).
Optical systems
One of the problems of the lighthouse lamps were to make the light visible from long distance and distinguishable by the seamen from other lights. Thus, the development of the optical systems began.The first solution to amplify the light intensity was the reflection. A flame was placed after a parabolic mirror that hold the light.
Later, lens that hold the rays of light in a parallel beam were used. However, the great innovation
was carried out by Agustín Fresnel who placed reflection prisms under and over the main lens so
that they reinforced the beam.
In order to distinguish the lights, the optical systems were built with panels. When these turned, the desired amount of glitters could be obtained. However, these cutting glass equipments were very heavy and hence, they were moved slowly. A vessel required some minutes (1-4 min) to recognise the light and, in some case, hardly counted the glitters correctly.
This problem was solved by placing the system on a mercury float. Thus, the friction was reduced and the turn speed increased. Nowadays, acrylic optical systems are used. They are very light and their size is smaller. Thus, excellent results are obtained.
In order to distinguish the lights, the optical systems were built with panels. When these turned, the desired amount of glitters could be obtained. However, these cutting glass equipments were very heavy and hence, they were moved slowly. A vessel required some minutes (1-4 min) to recognise the light and, in some case, hardly counted the glitters correctly.
This problem was solved by placing the system on a mercury float. Thus, the friction was reduced and the turn speed increased. Nowadays, acrylic optical systems are used. They are very light and their size is smaller. Thus, excellent results are obtained.
Lanterns
This system is based on the protection of the light. In the lighthouses fed by wood, the lanterns were a simple cupola supported vertically and protected partially with land. The oil lighthouses were protected by glasses placed on vertical mullions.The lantern shape was polygonal and sometime cylindrical. The number of sides matched the number of panels of the optical system. The mullion of the lantern and of the optical system also matched. Nevertheless, the vertical mullion caused undesired reflections and shadows during the turn. This problem was solved by using cylindrical lanterns with curved glasses and helicoid mullions.
The upper side of the lantern was covered with a metallic cupola, usually made of copper, opened in the upper area to allow the ventilation. When the cupola was transparent, the light was also used to guide the air navigation.