Screw-pile lighthouse - AbsoluteAstronomy.com

A screw-pile lighthouse is a lighthouse

Lighthouse

A lighthouse is a tower, building, or other type of structure designed to emit light from a system of lamps and lenses or, in older times, from a fire, and used as an aid to navigation for maritime pilots at sea or on inland waterways....

which stands on piles that are screw

Screw

A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...

ed into sandy or muddy sea or river bottoms. The first screw-pile lighthouse was built by blind Irish

Northern Ireland

Northern Ireland is one of the four countries of the United Kingdom. Situated in the north-east of the island of Ireland, it shares a border with the Republic of Ireland to the south and west...

engineer Alexander Mitchell

Alexander Mitchell (engineer)

Alexander Mitchell, was an Irish engineer who from 1802 was blind. He is known as the inventor of the screw-pile lighthouse...

. It was constructed in 1838 at the mouth of the Thames and was known as the Maplin Sands

Maplin Sands

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...

lighthouse.

In the United States, screw-pile lighthouses proliferated in the Chesapeake Bay

Chesapeake Bay

The Chesapeake Bay is the largest estuary in the United States. It lies off the Atlantic Ocean, surrounded by Maryland and Virginia. The Chesapeake Bay's drainage basin covers in the District of Columbia and parts of six states: New York, Pennsylvania, Delaware, Maryland, Virginia, and West...

due to its estuarial soft bottom. North Carolina

North Carolina

North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...

's sounds and river entrances were also once home to many screw-pile lights. The characteristic design is a -story hexagonal wooden building with dormers and a cupola light room.

History

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

Alexander Mitchell (engineer)

Alexander Mitchell, was an Irish engineer who from 1802 was blind. He is known as the inventor of the screw-pile lighthouse...

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 the 1830s. The first screwpile lighthouse type built in the United States was at Brandywine Shoal

Brandywine Shoal Light

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, New Jersey...

, Delaware Bay

Delaware Bay

Delaware Bay is a major estuary outlet of the Delaware River on the Northeast seaboard of the United States whose fresh water mixes for many miles with the waters of the Atlantic Ocean. It is in area. The bay is bordered by the State of New Jersey and the State of Delaware...

, 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 were 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

American Civil War

The American Civil War was a civil war fought in the United States of America. In response to the election of Abraham Lincoln as President of the United States, 11 southern slave states declared their secession from the United States and formed the Confederate States of America ; the other 25...

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 power 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

Florida Keys

The Florida Keys are a coral archipelago in southeast United States. They begin at the southeastern tip of the Florida peninsula, about south of Miami, and extend in a gentle arc south-southwest and then westward to Key West, the westernmost of the inhabited islands, and on to the uninhabited Dry...

, 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 diffuses 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-story wooden dwelling) screwpile lighthouses were built throughout the Carolina sounds, Chesapeake Bay

Chesapeake Bay

, Delaware Bay

Delaware Bay

, along the Gulf of Mexico

Gulf of Mexico

The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

, at least two in Long Island Sound

Long Island Sound

Long Island Sound is an estuary of the Atlantic Ocean, located in the United States between Connecticut to the north and Long Island, New York to the south. The mouth of the Connecticut River at Old Saybrook, Connecticut, empties into the sound. On its western end the sound is bounded by the Bronx...

and one even at Maumee Bay

Maumee Bay

Maumee Bay on Lake Erie is located in the U.S. state of Ohio, just east of the city of Toledo. The bay and the surrounding wetlands form most of the Maumee River basin, and in 1975 part of the area was incorporated into Maumee Bay State Park. The park is not huge, covering , but its wetlands...

(1855), Lake Erie

Lake Erie

Lake Erie is the fourth largest lake of the five Great Lakes in North America, and the tenth largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also has the shortest average water residence time. It is bounded on the north by the...

, Ohio

Ohio

Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...

. 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

Louisiana

Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...

prior to the Civil War.

Surviving examples

Built in 1885, the Middle Bay Light
Middle Bay Light
Middle Bay Light, also known as Middle Bay Lighthouse and Mobile Bay Lighthouse, is a hexagonal-shaped screw-pile lighthouse offshore from Mobile, Alabama, in the center of Mobile Bay.-History:...

in Alabama's
Alabama
Alabama is a state located in the southeastern region of the United States. It is bordered by Tennessee to the north, Georgia to the east, Florida and the Gulf of Mexico to the south, and Mississippi to the west. Alabama ranks 30th in total land area and ranks second in the size of its inland...

Mobile Bay
Mobile Bay
Mobile Bay is an inlet of the Gulf of Mexico, lying within the state of Alabama in the United States. Its mouth is formed by the Fort Morgan Peninsula on the eastern side and Dauphin Island, a barrier island on the western side. The Mobile River and Tensaw River empty into the northern end of the...

is an example of a common screw-pile lighthouse.
The Seven Foot Knoll Light
Seven Foot Knoll Light
The Seven Foot Knoll Light was built in 1855 and is the oldest screw-pile lighthouse in Maryland. It was initially installed on a shallow shoal, Seven Foot Knoll, at the mouth of the Patapsco River...

was built in 1856 and is the oldest screwpile lighthouse in Maryland. It was initially 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
Thomas Point Shoal Light
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...

is a historic lighthouse in the Chesapeake Bay on the east coast of the United States, and the most recognized lighthouse in Maryland.
Carysfort Reef Light
Carysfort Reef Light
Carysfort Reef Light is located approximately six nautical miles east of Key Largo, Florida. The lighthouse has an iron screw-pile foundation with a platform, and a skeletal octagonal pyramidal tower, which is painted red. The light is 100 feet above the water. The original lens was a first order...

, four miles east of Key Largo
Key Largo
Key Largo is an island in the upper Florida Keys archipelago and, at long, the largest of the Keys. It is also the northernmost of the Florida Keys in Monroe County, and the northernmost of the Keys connected by U.S. Highway 1...

, Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...

, was built in 1852 and is the oldest screw-pile (with disk) lighthouse still in service in the United States. Screw-pile lighthouses on the reefs in Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...

are tall skeletal towers, with living and working quarters set high above the reach of storm waves.
Fowey Rocks Light
Fowey Rocks Light
Fowey Rocks Light is located seven miles southeast of Cape Florida on Key Biscayne. The lighthouse was completed in 1878, replacing the Cape Florida lighthouse. It was automated on May 7, 1974 and is still in operation today. The structure is cast iron, with a screw-pile foundation, a platform and...

, built in 1878, is seven miles south of Key Biscayne
Key Biscayne
Key Biscayne is an island located in Miami-Dade County, Florida, United States, between the Atlantic Ocean and Biscayne Bay. It is the southernmost of the barrier islands along the Atlantic coast of Florida, and lies south of Miami Beach and southeast of Miami...

, Florida.
American Shoal Light
American Shoal Light
The American Shoal Light is located east of the Saddlebunch Keys, close to Looe Key, in Florida, USA. 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.American Shoal Light is cast iron,...

, completed in 1880, is located east of the Saddlebunch Keys
Saddlebunch Keys
The Saddlebunch Keys are a series of mangrove islands about 7 miles east of Key West, Florida.The keys are scattered between Lower Sugarloaf Key and Shark Key.U.S...

, in the Florida Keys
Florida Keys
The Florida Keys are a coral archipelago in southeast United States. They begin at the southeastern tip of the Florida peninsula, about south of Miami, and extend in a gentle arc south-southwest and then westward to Key West, the westernmost of the inhabited islands, and on to the uninhabited Dry...

.
Gasparilla Island Light
Gasparilla Island Lights
The Gasparilla Island Lights are on Gasparilla Island in Boca Grande, Florida. The Port Boca Grande Light is on the south tip of Gasparilla Island, and marked the Boca Grande Pass entrance to Charlotte Harbor. It has also been known as the Gasparilla Island Light and the Boca Grande Light. The...

, built in 1890, is located in Boca Grande, Florida
Boca Grande, Florida
Boca Grande is a small residential community on Gasparilla Island, in southwest Florida. Gasparilla Island is a part of both Charlotte and Lee Counties, while the actual village of Boca Grande, which is home to many seasonal and some year-round residents, is entirely in the Lee County portion of...

.
The Roanoake River Light was built in 1877, and has been moved twice. It is the only surviving screw-pile lighthouse in North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...

.
Gunfleet Lighthouse
Gunfleet Lighthouse
Gunfleet Lighthouse is a 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. It is 74 feet in height and hexagonal in plan; mounted on seven piles forming a steel lattice and originally painted red...

off Frinton-on-Sea
Frinton-on-Sea
Frinton-on-Sea is a small seaside town in the Tendring District of Essex, England. It is part of the Parish of Frinton and Walton.-History:...

in Essex
Essex
Essex is a ceremonial and non-metropolitan county in the East region of England, and one of the home counties. It is located to the northeast of Greater London. It borders with Cambridgeshire and Suffolk to the north, Hertfordshire to the west, Kent to the South and London to the south west...

was constructed in 1850 but abandoned in 1921.

External links

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