A screw-pile lighthouse is a lighthouse which stands on piles that are screwed into sandy or muddy sea or river bottoms. The first screw-pile lighthouse to begin construction was built by blind Irish engineer Alexander Mitchell. Construction began in 1838 at the mouth of the Thames and was known as the Maplin Sands lighthouse, first lit in 1841. However, though its construction began the Wyre Light in Fleetwood, was the first to be lit. In the United States, several screw-pile lighthouses were constructed in the Chesapeake Bay due to its estuarial soft bottom. North Carolina's sounds and river entrances were once home to many screw-pile lights; the characteristic design is a 1 1⁄2-storey hexagonal wooden building with dormers and a cupola light room. Non-screwpile tubular skeletal tower lighthouses were built of cast-iron but of wrought-iron piles, both onshore and offshore on soft bottoms such as mud and swamp. Alexander Mitchell invented the screwpile, a major improvement over the standard straightpile construction type.
With his son, he patented his wrought-iron screwpile design in England in 1833. The Walde Lighthouse in northern France, established in 1859, was based on Mitchell's design. Although discontinued in 1998 and shorn of its lantern, it is the only remaining screwpile lighthouse in France; the first screwpile lighthouse type built in the United States was at Brandywine Shoal, Delaware Bay, an area served by a lightship since 1823 and an ordinary straightpile lighthouse which stood there in 1828 but was destroyed by ice. Major Hartman Bache, a distinguished engineer of the Army Corps of Topographical Engineers, began work in 1848 and completed the task in 1850, at a construction cost of $53,317. Alexander Mitchell served as consultant; the screwpiles were turned by a 4-foot capstan worked by 30 men. To protect the structure from ice floes an ice-breaker consisting of a pier of 30 iron screwpiles 23 feet long and five inches in diameter was screwed down into the bottom and interconnected at their heads above the water reinforcing them together.
Subsequently, the use of caisson lighthouses proved more durable in locations subject to ice. Screwpile lighthouses were inexpensive, easy to construct, comparatively quick to build, they became popular after the Civil War when the Lighthouse Board adopted a policy to replace inside light vessels with screwpile lighthouses. Most screwpile lighthouses were made with iron piles, though a few were made with wooden piles covered with metal screw sleeves; the typical screwpile lighthouse was hexagonal or octagonal in plan consisting of a central pile, set first and the six or eight perimeter piles were screwed in place around it. Metal screwpiles were used to form the foundation of many lighthouses built on sandy or muddy bottoms; the helicoidal or screw-like cast-iron flange at the end of the metal pile was augured into the bottom increasing the bearing capacity of the pile as well as its anchoring properties. Yet lighthouses built with these foundations were found to be vulnerable to ice floes. In areas such as the Florida Keys, where the bottom is soft coral rock, diskpile foundation lighthouses were built.
Wrought iron piles were driven through a cast-iron or semi-steel disk which rested on the sea floor until a shoulder on the pile prevented further penetration. The disk distributes the weight of the tower more evenly over the bottom. In coral reef areas where sand is prevalent, a cast-steel screw was fitted to the end of the pile to give it more anchoring ability. Cofferdams were used in shallow waters where it was not necessary to penetrate the natural bottom; the cofferdam enabled the water inside the dam to be pumped out and the foundation built "in the dry." As many as 100 spider-like, cottage-type screwpile lighthouses were built throughout the Carolina sounds, Chesapeake Bay, Delaware Bay, along the Gulf of Mexico, at least two in Long Island Sound and one at Maumee Bay, Lake Erie, Ohio. Few survive to this day; the tall offshore skeletal tower type was built in exposed open water at major coastal sites where visibility over ten miles was required. Six offshore skeletal towers were built in Florida.
Spit Bank Lighthouse, in Cork Harbour, Ireland was built by Alexander Mitchell between 1851 and 1853 and is still in use. Carysfort Reef Light, four miles east of Key Largo, was built in 1852 and was the oldest screw-pile lighthouse still in service in the United States, until is was deactivated in 2014. Screw-pile lighthouses on the reefs in Florida are tall skeletal towers, with living and working quarters set high above the reach of storm waves; the Seven Foot Knoll Light is the oldest screwpile lighthouse in Maryland. It was installed on a shallow shoal, Seven Foot Knoll, at the mouth of the Patapsco River; the northern reach of this river is the Baltimore Harbor, where the now-decommissioned lighthouse has been placed as a museum. The Thomas Point Shoal Light is a historic lighthouse in the Chesapeake Bay and the most recognized lighthouse in Maryland; the Drum Point Light located off Drum Point at the mouth of the Patuxent River, it is now an exhibit at the Calvert Marine Museum. The Hooper Strait Light located at the entrance to Tangier Sound, it is now
A daymark or a day marker is the daytime identifier of an aid to navigation or daybeacon. The daymark conveys to the mariner during daylight hours the same significance as does the aid's light or reflector at night. Buoy Day beacon Landmark Sea mark Lighthouse Lightvessel Trinity House Obelisk
A lighthouse museum is a museum specializing in the display of historical objects relating to lighthouses. These museums are either stand alone buildings or are present in lighthouses that are active or inactive. Objects displayed include tools lighthouse keepers used at the time in their everyday lives to maintain the light as well as historic objects such as the Fresnel lens. In addition to navigation, lighthouses in general continue to operate as "small maritime museums"; the following is a list of lighthouse museums. All of these entries are located on lighthouse property which may or may not be run, these areas include the lighthouse tower, keepers residence, other buildings that were built to aid; the entries on this list include reliable sources that must mention a "lighthouse museum" on the given property. National Lighthouse Museum - New York, USA North Carolina Maritime Museum - North Carolina, USA National Lighthouse Museum - South Korea Open-air museum A.^ The opening date refers to the current museum
A Fresnel lens is a type of compact lens developed by French physicist Augustin-Jean Fresnel for lighthouses. The design allows the construction of lenses of large aperture and short focal length without the mass and volume of material that would be required by a lens of conventional design. A Fresnel lens can be made much thinner than a comparable conventional lens, in some cases taking the form of a flat sheet. A Fresnel lens can capture more oblique light from a light source, thus allowing the light from a lighthouse equipped with one to be visible over greater distances; the idea of creating a thinner, lighter lens in the form of a series of annular steps is attributed to Georges-Louis Leclerc, Comte de Buffon. Whereas Buffon proposed grinding such a lens from a single piece of glass, the Marquis de Condorcet proposed making it with separate sections mounted in a frame. French physicist and engineer Augustin-Jean Fresnel is most given credit for the development of the multi-part lens for use in lighthouses.
According to Smithsonian magazine, the first Fresnel lens was used in 1823 in the Cordouan lighthouse at the mouth of the Gironde estuary. Scottish physicist Sir David Brewster is credited with convincing the United Kingdom to adopt these lenses in their lighthouses; the Fresnel lens reduces the amount of material required compared to a conventional lens by dividing the lens into a set of concentric annular sections. An ideal Fresnel lens would have an infinite number of sections. In each section, the overall thickness is decreased compared to an equivalent simple lens; this divides the continuous surface of a standard lens into a set of surfaces of the same curvature, with stepwise discontinuities between them. In some lenses, the curved surfaces are replaced with flat surfaces, with a different angle in each section; such a lens can be regarded as an array of prisms arranged in a circular fashion, with steeper prisms on the edges, a flat or convex center. In the first Fresnel lenses, each section was a separate prism.'Single-piece' Fresnel lenses were produced, being used for automobile headlamps, brake and turn signal lenses, so on.
In modern times, computer-controlled milling equipment might be used to manufacture more complex lenses. Fresnel lens design allows a substantial reduction in thickness, at the expense of reducing the imaging quality of the lens, why precise imaging applications such as photography still use larger conventional lenses. Fresnel lenses are made of glass or plastic. In many cases they are thin and flat flexible, with thicknesses in the 1 to 5 mm range. Modern Fresnel lenses consist of all refractive elements; however many of the lighthouses have both refracting and reflecting elements, as shown in the photographs and diagram. That is, the outer elements are sections of reflectors while the inner elements are sections of refractive lenses. Total internal reflection was used to avoid the light loss in reflection from a silvered mirror. Fresnel produced six sizes of lighthouse lenses, divided into four orders based on their size and focal length. In modern use, these are classified as first through sixth order.
An intermediate size between third and fourth order was added as well as sizes above first order and below sixth. A first-order lens has a focal length of a maximum diameter 2590 mm high; the complete assembly is 1.8 m wide. The smallest has a focal length of an optical diameter 433 mm high; the largest Fresnel lenses are called hyperradiant Fresnel lenses. One such lens was on hand when it was decided to outfit the Makapuu Point Light in Hawaii. Rather than order a new lens, the huge optic construction, 3.7 metres tall and with over a thousand prisms, was used there. There are two main types of Fresnel lens: non-imaging. Imaging Fresnel lenses use segments with curved cross-sections and produce sharp images, while non-imaging lenses have segments with flat cross-sections, do not produce sharp images; as the number of segments increases, the two types of lens become more similar to each other. In the abstract case of an infinite number of segments, the difference between curved and flat segments disappears.
Spherical A spherical Fresnel lens is equivalent to a simple spherical lens, using ring-shaped segments that are each a portion of a sphere, that all focus light on a single point. This type of lens produces a sharp image, although not quite as clear as the equivalent simple spherical lens due to diffraction at the edges of the ridges. Cylindrical A cylindrical Fresnel lens is equivalent to a simple cylindrical lens, using straight segments with circular cross-section, focusing light on a single line; this type produces a sharp image, although not quite as clear as the equivalent simple cylindrical lens due to diffraction at the edges of the ridges. Spot A non-imaging spot Fresnel lens uses ring-shaped segments with cross sections that are straight lines rather than circular arcs; such a lens does not produce a sharp image. These lenses have application such as focusing sunlight on a solar panel. Fresnel lenses may be used as components of Köhler illumination optics resulting in effective nonimaging optics Fresnel-Köhler solar concentrators.
Linear A non-imagin
A Dalén light is a light produced from burning of carbide gas, combined with a solar sensor which automatically operates the light only during darkness. The technology was the predominant form of light source in lighthouses from the 1900s through the 1960s, when electric lighting had become dominant; the system was invented by Gustaf Dalén and marketed by his company AGA. Dalén invented the AGA cooker in 1922; the Dalén light is notable because of its sun valve, which earned its inventor the Nobel prize in physics. The Carbide lamp was developed in the early 1900s. While the lamps proved useful in many applications, the problem of safely storing acetylene meant they needed regular refilling which constrained their use in applications such as lighthouses. Lighthouses using Dalén lighting have included: Barrenjoey Lighthouse, New South Wales Peninsula Point Light Upper Peninsula Michigan United States Point Stephens Light, New South Wales Celarain Lighthouse, Mexico Skerryvore Lighthouse, the Hebrides Recalada a Bahía Blanca Light, Argentina Terry Pepper, Seeing the Light – Lighthouses of the Western Great Lakes, Illumination
Conservation and restoration of lighthouses
The conservation and restoration of lighthouses is the process by which lighthouse structures are preserved through detailed examination, in-kind replacement of materials. Given the wide variety of materials used to construct lighthouses, a variety of techniques and considerations are required. Lighthouses alert sea goers of rocky shores nearby as well as to provide landmark navigation. Lighthouses act as a physical representation to maritime history and advancement; these historic buildings are prone to deterioration due to their location on rocky outcrops of land near the water, as well as severe weather events, the continued rise of sea levels. Given these conditions preservation and conservation efforts have increased; the ground consists of the land and landscape that the lighthouse property sits on. The grounds may include buildings from other time periods as part of the cultural landscape; the types of buildings, their relationship to one another, their location over the whole of the property, types of flora and their location, potential archaeological sites, are all aspects that are related to the lighthouse and its history and should be considered during conservation of the property.
Outbuildings are prone to deterioration because they were used for storage and were not maintained to the same standards as the lighthouse. Former repairs to buildings may have used inexpensive materials as a temporary fix; these materials degrade making the building unstable. Any buildings that remain intact and in their original location are important to the relationship and usage of the lighthouse. Materials and details are all representative of the lighthouse when it was active and are considered during the preservation process. Lighthouse exterior paint was used in colorful patterns to act as a day marker. Paint was used to help protect the exterior structure of the lighthouse from wear. Evidence of paint degradation include crazing, peeling between coats and wrinkling. Repair can be made through a complete replacement of the paint. Original paint was made of lead and tended to withstand harsh conditions while still protecting the structure; the required use of National Historic Preservation approved paints has proved difficult as they do not work well with the lighthouse structure's original materials Furthermore, salt in the air can lead to severe chalking of the paint surface and cause premature failure of latex paint products.
Most repainting projects will have to begin with removal of the original base coat, followed by a thorough surface cleaning to remove impurities ended with a complete repainting of the structure. Paint only lasts between five and eight years, depending on the lighthouse and conditions. Stucco has been traditionally used as a protective barrier on the exterior of lighthouses. Stucco is made up of fine granular particles mixed together with a binder; the composition of stucco has changed over the years and may require laboratory analysis to determine the makeup. Most of the problems with stucco arise from prolonged contact with water or moisture which breaks down the structure of the particles and binder. In addition, the texture of stucco is prone to removal; as with most preservation, gentle cleaning of the surface can help remove dirt and impurities and inhibit further deterioration. Iron was a popular material used in lighthouse construction. Multiple types of iron were used including: cast iron, wrought iron, galvanized iron, galvanized steel, stainless steel.
Cast iron was the most popular material because it resists corrosion and can be cast into a multitude of shapes. Though iron is sturdy it can be prone to deterioration through corrosion and flaws from the manufacturing process. Degradation of iron is visible through pitting, erosion, blistering and scaling. Preservation and restoration of iron should be completed using the least invasive approach possible. Iron is strong but can be damaged through improper or harsh procedures. "Many of the maintenance and repair techniques... those relating to cleaning and painting, are dangerous and should be carried out only by experienced and qualified workmen using protective equipment suitable to the task. It may be necessary to involve a USCG engineer or architect, preservation architect, or building conservator familiar with lighthouse preservation to assess the condition of the iron and prepare contract documents for its treatment." The masonry component of a lighthouse is made up of the stones on the exterior.
Damage to masonry is caused by water, salt accumulation and contraction, poor ventilation, inappropriate cleaning techniques. Masonry may show many signs of deterioration to include: bulges, efflorescence, flaking, sloping or uneven settlement, mold or mildew, missing stones or bricks, condensation buildup, blistering. Basic preservation of lighthouse masonry includes gentle surface cleaning. Appropriate methods for cleaning are determined by the type of masonry; some cleaning methods include water and laser. There are multiple water cleaning methods. Soaking is a process where the masonry undergoes a prolonged exposure to misting water to remove dirt. Water washing uses a light to medium pressurized stream of water; some water washing may use the addition of detergents to increase dirt removal. Chemical cleaning is an option, but may be too harsh depending on the makeup of the masonry. Chem
A sector light is a man-made pilotage and position fixing aid that consists of de-limited horizontal angle light beams to guide water-borne traffic through a safe channel at night in reasonable visibility. Sector lights are most used for safe passage through shallow or dangerous waters; this may be when entering harbour. Nautical charts give all the required information. Sectors of colored glass are placed in the lanterns of these lights; the light will show these colors when observed certain bearings. Bearings referring to a sector are given in degrees true as observed from sea. Though the colors of the light will change, the characteristics will not; the change of color is not abrupt. The transition is made through an arc of uncertainty of 2° or greater; the colors that are used, are conform to the IALA Maritime Bouyage system, designed by the International Association of Lighthouse Authorities: white - this sector is in the middle of the safe channel red - indicates the port edge of the channel for vessels approaching the light source green - indicates the starboard edge of the channel for vessels approaching the light source.
A ship, sailing in safe water and sees the red color of the light has to make an alteration in course. The world has different navigation stereotypes managed by IALA. For example, the United States uses a signalling stereotype, the opposite of Europe. In USA, the red light indicates the starboard side of the channel for harbour bound vessels, while the green light indicates the port side of the same channel. An expression to remind of this is "red right returning". An example of a sector light is the light of the Fisgard Lighthouse in British Columbia; the lighthouse as built to guide ships through the entrance of Esquimalt harbour. The white sector is an isophase light of 2s from 322° to 195°. If the ship sees this white light, it can pass safely; the rest shows a red light from 195 to 322°. If a vessel sees this light, it should alter its course. Another example is the PEL sector light at Diego Garcia; the PEL sector light was constructed to guide US Navy vessels into the Diego Garcia port through a narrow entrance in the lagoon.
The PEL sector light is visible for 10 nautical miles by day. The beam with 3 colors is narrow at 1.6°. This was required because the PEL sector light was built over 7NM from the atoll entrance and it had to illuminate a safe entrance, only 228 meters wide