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 the blind Irish engineer Alexander Mitchell. Construction began in 1838 at the mouth of the Thames and was known as the Maplin Sands lighthouse, and first lit in 1841. [1] However, though its construction began later, the Wyre Light in Fleetwood, Lancashire, was the first to be lit (in 1840). [1]
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 also once had 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 (straightpile) tubular skeletal tower lighthouses were built, usually of cast-iron but also of wrought-iron piles, both onshore and offshore, typically on soft bottoms such as mud, sand, 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. [2] The Walde Lighthouse in northern France (Pas-de-Calais), 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 briefly 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, though, the use of caisson lighthouses proved more durable in locations subject to ice.
Screwpile lighthouses were relatively inexpensive, easy to construct, and comparatively quick to build. They became especially popular after the Civil War when the Lighthouse Board adopted a policy to replace inside (bays, sounds, and rivers) 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 (these sleeves were probably adopted because they were less expensive and easier to insert into the bottom, plus the sleeve protected the wood from marine-boring invertebrates). The typical screwpile lighthouse was hexagonal or octagonal in plan consisting of a central pile which was set first and then 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 also prevalent, a cast-steel screw was fitted to the end of the pile to give it more anchoring ability. Cofferdams were used generally in shallow waters where it was not necessary to deeply penetrate the natural bottom. The cofferdam enabled the water inside the dam to be pumped out and the foundation built "in the dry".
Perhaps as many as 100 spider-like, cottage-type (1½-storey wooden dwelling) 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 even at Maumee Bay (1855), Lake Erie, Ohio. Few survive to this day; many were replaced with caisson-type lighthouses. 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; three before and three after the American Civil War, as well as one in the Gulf of Mexico off Louisiana prior to the Civil War.
A lighthouse is a tower, building, or other type of physical structure designed to emit light from a system of lamps and lenses and to serve as a beacon for navigational aid, for maritime pilots at sea or on inland waterways.
The Seven Foot Knoll Light was built in 1855 and is the oldest screw-pile lighthouse in Maryland. It was located atop Seven Foot Knoll in the Chesapeake Bay until it was replaced by a modern navigational aid and relocated to Baltimore's Inner Harbor as a museum exhibit.
The Maplin Sands are mudflats on the northern bank of the Thames estuary, off Foulness Island, near Southend-on-Sea in Essex, England, though they actually lie within the neighbouring borough of Rochford. They form a part of the Essex Estuaries Special Area of Conservation due to their value for nature conservation, with a large colony of dwarf eelgrass and associated animal communities.
The history of lighthouses refers to the development of the use of towers, buildings, or other types of structure, as an aid to navigation for maritime pilots at sea or on inland waterways.
The Thomas Point Shoal Light, also known as Thomas Point Shoal Light Station, is a historic lighthouse in the Chesapeake Bay on the east coast of the United States, and the most recognized lighthouse in Maryland. It is the only screw-pile lighthouse in the bay which stands at its original site. The current structure is a 1½ story hexagonal wooden cottage, equipped with a foghorn as well as the light.
Carysfort Reef Light is located east of Key Largo, Florida. The lighthouse has an iron-pile foundation with a platform, and a skeletal, octagonal, pyramidal tower, which is painted red. The light was 100 feet (30 m) above the water. It was the oldest functioning lighthouse of its type in the United States until it was decommissioned in 2015, having been completed in 1852. The light last installed was a xenon flashtube beacon. It was added to the National Register of Historic Places in 1984.
The American Shoal Light is located east of the Saddlebunch Keys, just offshore from Sugarloaf Key, close to Looe Key, in Florida, United States. It was completed in 1880, and first lit on July 15, 1880. The structure was built to the same plan and dimensions as the Fowey Rocks lighthouse, completed in 1878.
Sand Key Light is a lighthouse 6 nautical miles southwest of Key West, Florida, between Sand Key Channel and Rock Key Channel, two of the channels into Key West, on a reef intermittently covered by sand. At times the key has been substantial enough to have trees, and in 1900 nine to twelve thousand terns nested on the island. At other times the island has been washed away completely.
The Dames Point Light marked an 8-foot-deep (2.4 m) shoal at a sharp bend in the St. Johns River in Florida that was a danger to ships heading to or from Jacksonville.
The unmanned reef lights of the Florida Keys were navigational aids erected near the Florida Keys between 1921 and 1935. They were intended to mark local hazards and did not need to be visible for as far as the reef lights that were erected near the Keys during the 19th century. By the time the lights in this list were erected, older lighthouses were being automated, and these new lights were designed to be automated from the start. The lights resembled the older reef lights in having a wrought iron skeletal pyramidal structure on a screw-pile foundation. They all originally had lanterns on their peaks, so that they looked like smaller versions of the older reef lights, but had no keeper's quarters.
A pile lighthouse is a type of lighthouse found in Australia and the United States. In the United States they are found primarily in Florida, including on open reefs adjacent to the Florida Keys.
Solomons Lump Light is a lighthouse in the Chesapeake Bay, the abbreviated remains of a caisson light built in 1895. That structure replaced a screw-pile light built on the same spot in 1875, which in turn superseded the Fog Point Light.
Greenbury Point Light was the name of two lighthouses in the Chesapeake Bay, both located at the mouth of the Severn River in Annapolis, Maryland.
Drum Point Light Station also known as Drum Point Lighthouse is one of four surviving Chesapeake Bay screw-pile lighthouses. Originally located off Drum Point at the mouth of the Patuxent River, it is now an exhibit at the Calvert Marine Museum.
The Wyre Light was a 40-foot (12 m) tall iron screw-pile lighthouse marking the navigation channel to the town of Fleetwood, Lancashire, England.
The Brandywine Shoal Light is a lighthouse on the north side of the ship channel in Delaware Bay on the east coast of the United States, west of Cape May, Cape May County, New Jersey, United States. It was the site of the first screw-pile lighthouse in the United States.
The One Fathom Bank Lighthouse refers to two offshore lighthouses in the Strait of Malacca, specifically, on a shoal within Malaysian waters, dubbed One Fathom Bank, off the coast of the state of Selangor.
Gunfleet Lighthouse is a derelict screw-pile lighthouse lying in the North Sea, six miles off the coast at Frinton-on-Sea in Essex, constructed in 1850 by James Walker of Trinity House. George Henry Saunders was the contractor. Walker and Burges were the Engineers. It is 74 feet (23 m) in height and hexagonal in plan; mounted on seven piles forming a steel lattice and originally painted red. It was first lit on 1 May 1856, replacing a light vessel which had been on station there since 1850.
The Ship Shoal Light is a screw-pile lighthouse located in the Gulf of Mexico southwest of the Isles Dernieres off the coast of Louisiana. It is currently abandoned.
The Spit Bank Lighthouse close to Cobh in County Cork, Ireland is a screw-pile lighthouse which marks a shallow bank in the navigable channels of lower Cork Harbour. The platform was built by the blind Irish engineer Alexander Mitchell, with the lighthouse itself designed by George Halpin. In use since its completion between 1851 and 1853, and renovated as recently as 2013, the landmark structure marks the boundary of compulsory pilotage for large vessels entering the Port of Cork.
[Maplin Sands] was not, however, the first screw-pile lighthouse actually erected, for during the long preparation process which was carried on at Maplin Sands, a structure of the same principle had been begun and completed at Port Fleetwood...