The lighthouse won’t stand over to night. She shakes two feet each way now. -- J.W. + J.A
The two keepers of Minot’s Light (see drawing on left), situated on a 23-foot wide ledge off the Massachusetts Coast, wrote these words the night of April 16, 1851. A storm so terrible it turned the city of Boston, Massachusetts into an island was gradually destroying the many-legged 65-foot lighthouse, snapping the iron pilings one by one.
The trapped lighthouse keepers put their note into a proverbial bottle in the hope that someone would find it and know what had happened. Neither they nor the lighthouse survived: the two bodies were discovered on local beaches while the structure came to rest on the ocean floor. See more here and, for amateur historians, consult the Cohasset Historical Society.
How did this happen? One newspaper wrote of “… the weakness of theoretical science…” The story is one of ill-fated innovation arising from cost constraints, need for quick completion, and errors.
Engineering math software can mitigate some of these traditional sources of risk – as well as new ones [Infographic]. A disaster such as this has many sources, including lack of proper tools, poor logic, inexperience, unwise follow-on decisions, or just plain bad luck and misfortune. Using the right tools for the job, such as engineering math software, is a way to mitigate risk, helping you spot a bad design before it becomes an unsuccessful product.
When you combine engineering math software with CAD, you have a digital engineering notebook: a way to remove hassle – and inadvertent error – from your process. You embed your calculations in your CAD model. The two travel with and update one another, so you spend your time engineering, not piecing together design intent.
Ledges, Weather, and Lighthouse Design
The ledges off Cohasset, MA have long threatened shipping to the port of Boston. Even today, boaters approach Boston Harbor – and the local shoreline – with caution. By the mid-19th century relentless citizen petitions persuaded Congress to appropriate money for a lighthouse on Outer Minot’s Ledge.
Design constraints were unusual.
The ledge was under water up to 20 hours a day and exposed to the worst of the Atlantic storms from fall to spring. Lighthouses in England which faced similar conditions were built as stone towers, and popular wisdom leaned, as it were, in that direction. But Congress had appropriated only 1/8th of the money needed to do that – a paltry 39K.
The engineer chosen was Captain William H. Swift of the U.S. Army Topographical Engineers, who later had a very successful career in the canal and railroad industries. He brought to the project well-regarded experience and had distinguished himself by entering West Point when only 13.
Captain Swift decided that the edge was too small for stone tower to work. Instead, he proposed that using thin iron ‘legs’ would allow the waters to pass through. It would be also be cheaper than stone. The committee agreed.
But Captain Smith had adapted his design from iron-piling lighthouses in Europe, none of which stood on off-shore ledges. For this project, only workers who could swim were hired because waves could and did wash them off the job site.
The finished lighthouse had problems. The first lighthouse keeper and his assistants (both seasoned men) quit: they feared for their lives and the structure’s swaying made them miserably ill. Questions arose. Captain Swift took to the newspapers (although he’d had doubts) and stood by the design. A year and a half later, the April 1851 storm destroyed it. Captain Swift’s own drawing after the disaster shows only a few feet of iron piling remaining on the bare ledge.
The Successful Design
The new Minot’s Light is a 114-foot granite stone tower built at a cost of 300K, making it the most expensive American lighthouse ever built to that point.
It still stands, an invaluable aid to mariners and a popular destination – in calm weather – for recreational boaters of all kinds. A memorial to the two men killed in the tragedy, Joseph Antoine and Joseph Wilson, can be found on Government Island in Cohasset Harbor.