Spark-Plug and Texas-Tower Lighthouses
Two American Solutions to Open Water
American lighthouse engineering in the second half of the nineteenth and the first half of the twentieth centuries produced two forms that are immediately recognisable to anyone who has sailed or driven along the northeastern coast: the spark-plug lighthouse, a compact cylinder of iron and masonry rising from a round caisson base, and the Texas-tower lighthouse, an offshore platform structure whose superstructure sits on legs rising from the seabed. Both forms are responses to the same general challenge — providing a staffed, operational lighthouse in open or semi-exposed water where the ground conditions and depth ruled out conventional masonry construction — but they solved it with different technologies for different depths and exposures.
The names are colloquial. Neither the Lighthouse Board nor the Coast Guard used these terms in official documents. "Spark-plug" derives from the profile of the caisson-and-cylinder structures, which do resemble an automobile spark plug when seen from a distance: broad base, narrow shaft, bulbous lantern room at the top. "Texas tower" derives from the similarity of the deep-water platform structures to the offshore oil drilling rigs that were first developed in shallow Texas Gulf Coast waters in the late 1940s; when the Coast Guard began using similar technology for lighthouse construction in the 1960s, the colloquial name followed naturally.
The Spark-Plug Form
The spark-plug lighthouse emerged from the Lighthouse Board's work on caisson foundations in the 1880s, when the destruction of screwpile lighthouses by winter ice in Chesapeake Bay, Long Island Sound and the Delaware River made a more robust foundation system necessary. The caisson — a hollow cast-iron cylinder sunk onto the seabed and filled with concrete — provided both a foundation and the lowest section of the structure. Above the caisson, the cylindrical form continued in cast-iron plates bolted together, housing the keeper's quarters, the machinery rooms and the lamp room in a vertical stack of interlocking spaces connected by an internal stair.
The resulting structure is extraordinarily compact. A typical spark-plug lighthouse of the late nineteenth or early twentieth century occupies a footprint of roughly 8 to 12 metres in diameter and rises to a focal plane of 12 to 18 metres above mean high water. Within that volume, the original designs provided accommodation for a keeper and one or two assistants, with separate rooms for sleeping, cooking and watch-keeping, a machine room for the fog signal compressors, oil storage for the light, and all the technical equipment required to maintain a Fresnel lens and fog signal. The economy of space makes these structures the maritime equivalent of a narrowboat or a ship's cabin: everything necessary, nothing extraneous.
Notable Spark-Plug Lighthouses
Duxbury Pier lighthouse in Plymouth Harbour, Massachusetts, completed in 1871, is an early example of the form and one of the best preserved in New England. Known locally as "Bug Light" for its silhouette, it stands at the inner end of Duxbury Bay on a caisson foundation and retains its original fourth-order Fresnel lens. The light was automated in 1964 and fell into disrepair before being restored by the Duxbury Rural and Historical Society, which completed a major rehabilitation in 2001 that repainted the exterior in its original red, repaired the cast-iron plating and restored the lantern room.
The Stamford Harbour lighthouse in Connecticut, built in 1882, and the New London Ledge lighthouse in Connecticut, completed in 1909, represent opposite ends of the aesthetic range within the spark-plug tradition. Stamford is a utilitarian cylinder; New London Ledge is an architectural extravagance, its upper sections built in a French Second Empire style with a mansard roof, dormers and elaborate cast-iron detailing at a cost that embarrassed the Lighthouse Board. New London Ledge sits on a concrete caisson foundation in the Thames River approach and is now the subject of a preservation programme by the New London Maritime Society.
The Race Rock lighthouse at the convergence of Long Island Sound and the waters east of Fishers Island, completed in 1879, used a different foundation technique that bridges the gap between caisson and rock construction: the site had an existing submerged reef, and the contractors, led by Francis Hopkinson Smith, built an artificial island of granite rubble on top of the reef before constructing the granite tower and keeper's dwelling above it. The work took seven years and was among the most costly lighthouse construction projects in American history to that date.
Ambrose Light and the Texas-Tower Type
By the mid-twentieth century the American lighthouse service faced positions that exceeded the capabilities of the caisson form. The outer approaches to major ports required lights at distances from shore that put the seabed too deep for caisson construction and too far from land for any structure resting on a pile foundation of manageable dimensions. The answer came from the offshore oil industry: a structure on legs.
The Texas-tower concept applied to lighthouses involves prefabricating a working platform at a shipyard, transporting it to the site on a barge, setting the legs on the seabed at the required position, and then completing the platform fitout in situ. The resulting structure is essentially an offshore industrial platform modified for lighthouse use: helicopter deck, diesel generators, accommodation, fog signal equipment and lantern room in a compact and heavily engineered superstructure supported by tubular steel legs.
Ambrose Light, established at the entrance to New York Harbour in 1967 as the replacement for the Ambrose lightship, was the first Texas-tower lighthouse in American waters. The structure sits in 15 metres of water on the Ambrose Channel centreline 10 kilometres south-east of Sandy Hook and provides a light visible for 24 nautical miles, a fog signal and a radiobeacon. Its construction and outfitting cost significantly more than any previous lighthouse project, but the operating savings from eliminating a lightship crew and its attendant logistics justified the capital expenditure in the Coast Guard's analysis.
Buzzards Bay Light
Buzzards Bay lighthouse, also known as Cleveland East Ledge lighthouse and sometimes called the Buzzards Bay Entrance Light, was completed in 1961 and stands at the southern entrance to the Cape Cod Canal. It is a transitional form between the spark-plug and the full Texas-tower type: a cylindrical concrete caisson base, but with the living quarters and equipment spaces in a concrete superstructure of considerable height that places the focal plane 26 metres above mean high water. The tower is painted white with a broad red horizontal band, providing a distinctive daymark at the southern entrance to one of the busiest commercial waterways in New England.
The Buzzards Bay lighthouse was unmanned at the time of completion — a relatively early example of a new offshore structure being designed from the outset for unattended operation, in contrast to the practice that prevailed throughout the nineteenth century and most of the first half of the twentieth, when offshore lighthouses were staffed essentially by definition.
Platform Structures and Their Limitations
Texas-tower and platform-type lighthouses have a significant structural vulnerability that rock and caisson structures do not share: fatigue cracking in the steel leg joints caused by the cyclic loading of wave and current action. The failure mode is insidious because it is not visible until a crack has progressed to a size that threatens structural integrity, and inspection of the submerged joint areas requires divers or remotely operated vehicles.
The Ambrose Light structure, inspected periodically by Coast Guard and contract divers, has required significant leg repair and reinforcement work over its operational life. The similar platform structures of the North Sea oil industry have demonstrated both the severity of the fatigue problem and the effectiveness of monitoring and repair programmes in managing it. For lighthouse authorities, the lesson has been that platform structures require an inspection and maintenance commitment that is qualitatively different from masonry towers, and that the apparent simplicity of an automated offshore platform conceals substantial ongoing technical requirements.
The Current Survivors
A significant number of spark-plug lighthouses survive in American waters, mostly in New England, the Chesapeake and the Great Lakes. Many are listed on the National Register of Historic Places and several are the subjects of active preservation programmes. Open the map to locate spark-plug and Texas-tower lighthouses along the American northeast coast, where the concentration of lighthouse forms reflects the complexity of the navigation challenge — the shifting shoals, busy steamer lanes and winter ice conditions that drove American lighthouse engineers to develop forms found nowhere else in the world.
The Texas-tower types are fewer in number and mostly still active, their maintenance managed by the Coast Guard under long-term capital programmes. The surviving spark-plug lighthouses, particularly those that have been transferred to preservation organisations under the National Historic Lighthouse Preservation Act, represent a more immediate heritage challenge: cast-iron structures in salt water that require regular inspection, coating maintenance and structural attention to remain sound for another generation.