lighthouse
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What is a lighthouse?
A lighthouse is a structure, often a tower, built on land or on the seabed to help ships navigate coastal waters. They warn mariners of hazards, help them find their position, and guide them to their destinations. Mariners can identify a lighthouse from the sea by its shape, color, light color/flash patterns, or radio signals.
Most lighthouses use rhythmic flashes to create a unique signal, called the light's character, which repeats at specific intervals. These patterns can be a single flash, repeated groups of flashes, or a light that is normally on but momentarily turns off. The structures are painted distinct colors to stand out.
Modern lighthouses started being developed around 1700, with better structures and lighting. Today, lighthouses often include a helipad to allow for helicopter servicing and maintenance.
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Why are lighthouses important for coastal areas?
Lighthouses are crucial for coastal areas because they serve as aids to maritime coastal navigation, alerting mariners to hazards, confirming their location, and directing them to their destinations. They can be identified by their shape, color, light color/flash patterns, or radio signals.
While electronic navigation is more common, mariners often prefer visual navigation. Lighthouses have the advantages of simplicity, reliability, and low cost, and can be used by vessels without special equipment, providing a crucial backup. They guide navigators through busy coastal waters and harbor approaches. Most lighthouses use rhythmic flashes or eclipses to provide an identification signal. Fixed lights offer directional information in ports and harbors.
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How do lighthouses help ships navigate safely?
Lighthouses aid ships in coastal navigation by serving as maritime guides, alerting mariners to hazards and helping them determine their position. From the sea, ships can identify a lighthouse by its structure's shape and color, the light's color and flash pattern, or the radio signal's coded pattern. Most lighthouses use rhythmic flashes or eclipses to create a unique light character, with intervals regulated by international agreements. Mariners navigate by aligning their vessel to keep two range lights of different elevations in a single line. Shore lighthouses are often painted white, while those in the open sea use contrasting color bands for visibility.
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What is a lighthouse beacon and how does it work?
A lighthouse beacon is a structure, typically a tower, built on land or seabed to help ships navigate coastal waters. It warns mariners of hazards, helps them establish their position, and guides them to their destinations. From the sea, a lighthouse is identifiable by its shape, color, light color/flash pattern, or radio signal code. The lighthouse beacon supplies light to guide mariners. Early beacons used wood fires or torches, but later beacons used candles or oil lamps within glass or horn lanterns.
Electronic navigation systems have reduced the need for powerful lights, especially for landfall. However, minor lights and lighted buoys are still essential for navigating busy coastal waters and harbors. Mariners often prefer visual navigation for reassurance, and lighted marks offer simplicity, reliability, and low cost, serving as a backup for vessels without special equipment.
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How do lighthouse designs differ for various coastlines?
Lighthouse designs are influenced by their specific coastal environments. For lighthouses built on soft ground, the submerged caisson method is used. This involves positioning a steel, open-ended cylinder on the seabed, excavating sand for sinking, and filling it with concrete to create a solid base.
In situations where the seabed is suitable, a "float out" lighthouse can be built. This consists of a cylindrical tower on a large concrete base, towed to its position, and sunk onto the seabed.
Another design involves conventional steel-piled structures, similar to those used for offshore gas and oil rigs, offering greater independence from seabed conditions. The color and shape of a lighthouse also helps seafarers identify it. The Bishop Rock Lighthouse, constructed of interlocking granite blocks, is designed to withstand heavy seas.
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What modern technologies are used in coastal navigation besides lighthouses?
Beyond lighthouses, modern coastal navigation relies on several technologies. Global Positioning System (GPS) uses satellite signals to determine a vessel's longitude, latitude, and altitude. Loran C, a long-range radio navigation system, identifies a position through precise time-difference measurements of pulsed signals. Radar is also used to avoid collisions by allowing navigators to see other vessels regardless of visibility conditions. Additionally, electronic charts display coasts, sea depths, obstacles, and navigational aids.
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lighthouse, structure, usually with a tower, built onshore or on the seabed to serve as an aid to maritime coastal navigation, warning mariners of hazards, establishing their position, and guiding them to their destinations. From the sea a lighthouse may be identified by the distinctive shape or color of its structure, by the color or flash pattern of its light, or by the coded pattern of its radio signal. The development of electronic navigation systems has had a great effect on the role of lighthouses. Powerful lights are becoming superfluous, especially for landfall, but there has been a significant increase in minor lights and lighted buoys, which are still necessary to guide the navigator through busy and often tortuous coastal waters and harbor approaches. Among mariners there is still a natural preference for the reassurance of visual navigation, and lighted marks also have the advantages of simplicity, reliability, and low cost. In addition, they can be used by vessels with no special equipment on board, providing the ultimate backup against the failure of more sophisticated systems.
History of lighthouses
Lighthouses of antiquity
The forerunners of lighthouses proper were beacon fires kindled on hilltops, the earliest references to which are contained in the Iliad and the Odyssey (c. 8th century bce). The first authenticated lighthouse was the renowned Pharos of Alexandria, which stood some 350 feet (about 110 meters) high. The Romans erected many lighthouse towers in the course of expanding their empire, and by 400 ce there were some 30 in service from the Black Sea to the Atlantic. These included a famous lighthouse at Ostia, the port of Rome, completed in 50 ce, and lighthouses at Boulogne, France, and Dover, England. A fragment of the original Roman lighthouse at Dover still survives.
The Phoenicians, trading from the Mediterranean to Great Britain, marked their route with lighthouses. These early lighthouses had wood fires or torches burning in the open, sometimes protected by a roof. After the 1st century ce, candles or oil lamps were used in lanterns with panes of glass or horn.
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Medieval lighthouses
The decline of commerce in the Dark Ages halted lighthouse construction until the revival of trade in Europe about 1100 ce. The lead in establishing new lighthouses was taken by Italy and France. By 1500, references to lighthouses became a regular feature of books of travel and charts. By 1600, at least 30 major beacons existed.
These early lights were similar to those of antiquity, burning mainly wood, coal, or torches in the open, although oil lamps and candles were also used. A famous lighthouse of this period was the Lanterna of Genoa in Italy, probably established about 1139. It was rebuilt completely in 1544 as the impressive tower that remains a conspicuous seamark today. The keeper of the light in 1449 was Antonio Columbo, uncle of the Columbus who crossed the Atlantic. Another early lighthouse was built at Meloria, Italy, in 1157, which was replaced in 1304 by a lighthouse on an isolated rock at Livorno. In France the Roman tower at Boulogne was repaired by the emperor Charlemagne in 800. It lasted until 1644, when it collapsed owing to undermining of the cliff. The most famous French lighthouse of this period was one on the small island of Cordouan in the estuary of the Gironde River near Bordeaux. The original was built by Edward the Black Prince in the 14th century. In 1584 Louis de Foix, an engineer and architect, undertook the construction of a new light, which was one of the most ambitious and magnificent achievements of its day. It was 135 feet in diameter at the base and 100 feet high, with an elaborate interior of vaulted rooms, richly decorated throughout with a profusion of gilt, carved statuary, and arched doorways. It took 27 years to build, owing to subsidence of the apparently substantial island. By the time the tower was completed in 1611, the island was completely submerged at high water. Cordouan thus became the first lighthouse to be built in the open sea, the true forerunner of such rock structures as the Eddystone Lighthouse.
The influence of the Hanseatic League helped increase the number of lighthouses along the Scandinavian and German coasts. At least 15 lights were established by 1600, making it one of the best-lighted areas of that time.
During this period, lights exhibited from chapels and churches on the coast frequently substituted for lighthouses proper, particularly in Great Britain.
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The beginning of the modern era
The development of modern lighthouses can be said to have started about 1700, when improvements in structures and lighting equipment began to appear more rapidly. In particular, that century saw the first construction of towers fully exposed to the open sea. The first of these was Henry Winstanley’s 120-foot-high wooden tower on the notorious Eddystone Rocks off Plymouth, England. Although anchored by 12 iron stanchions laboriously grouted into exceptionally hard red rock, it lasted only from 1699 to 1703, when it was swept away without a trace in a storm of exceptional severity; its designer and builder, in the lighthouse at the time, perished with it. It was followed in 1708 by a second wooden tower, constructed by John Rudyerd, which was destroyed by fire in 1755. Rudyerd’s lighthouse was followed by John Smeaton’s famous masonry tower in 1759. Smeaton, a professional engineer, embodied an important new principle in its construction whereby masonry blocks were dovetailed together in an interlocking pattern. Despite the dovetailing feature, the tower largely relied on its own weight for stability—a principle that required it to be larger at the base and tapered toward the top. Instead of a straight conical taper, though, Smeaton gave the structure a curved profile. Not only was the curve visually attractive, but it also served to dissipate some of the energy of wave impact by directing the waves to sweep up the walls.
Owing to the undermining of the foundation rock, Smeaton’s tower had to be replaced in 1882 by the present lighthouse, constructed on an adjacent part of the rocks by Sir James N. Douglass, engineer-in-chief of Trinity House. In order to reduce the tendency of waves to break over the lantern during severe storms (a problem often encountered with Smeaton’s tower), Douglass had the new tower built on a massive cylindrical base that absorbed some of the energy of incoming seas. The upper portion of Smeaton’s lighthouse was dismantled and rebuilt on Plymouth Hoe, where it still stands as a monument; the lower portion or “stump” can still be seen on the Eddystone Rocks.
Following the Eddystone, masonry towers were erected in similar open-sea sites, which include the Smalls, off the Welsh coast; Bell Rock in Scotland; South Rock in Ireland; and Minots Ledge off Boston, Massachusetts, U.S. The first lighthouse of the North American continent, built in 1716, was on the island of Little Brewster, also off Boston. By 1820 there were an estimated 250 major lighthouses in the world.