How the oldest sea-washed lighthouse still protects sailors

Since 1811, the lamps of the Bell Rock Lighthouse in the North Sea (about 12 miles southeast of Arbroath, Scotland), have warned sailors to beware the infamous sunken reef known as the Bell Rock off the east coast of Scotland. 

Building on top of that rock was fraught with difficulties and danger. The rock is 12 miles off the coast in the fierce North Sea, and completely submerged except for a few hours each day. 

That the Bell Rock Lighthouse has endured the constant assault of the waves for 200 years without any significant deterioration to its masonry is testimony to the genius of Scottish engineer Robert Stephenson.

The lighthouse remains a tribute to the masons, joiners, smiths, mould-makers, stonecutters and carpenters who, with unsurpassed skill and courage, and at great personal risk, undertook its construction over four years. 

Credit: National Library of Scotland 

The Scottish coastline, with its submerged rocky moraines, is known for its hazards to navigation. The Bell Rock, (also known as Inchcape Rock) extends 427 metres across the shipping routes between the firths of the Forth and Tay, and is particularly insidious because, except at low tides, it lies completely hidden by the waves. 

From the earliest days of sail, shipwrecks here were common. A local legend tells of a 14th century abbot of Aberbrothock (modern Arbroath) who ordered a bell to be hung on a timber buoy attached to the rock, where its clanging in the restless waves would serve as a warning. 

The structure gave the rock its name, but did not last long. By the 18th century, ship losses on the coasts around Britain were so frequent that merchants lobbied Parliament in Westminster to build lighthouses. This led to the establishment, in 1786, of the Northern Lighthouse Trust. 

Credit: Flickr 

In 1799 Robert Stephenson, then a young civil engineer eager to make his name, first proposed a lighthouse on the Bell Rock, but it was not until 1804, when the Royal Navy Ship HMS York foundered there, costing 491 lives, that the sceptical Lighthouse Board agreed to the expensive (and many believed, foolhardy) project. 

Stephenson already had some experience—when he was just 19, he had supervised construction of a lighthouse at Little Cumbrae on the Firth of Clyde—but he was still relatively unknwon and so the cuatious Lighthouse Board appointed John Rennie, an eminent engineer of the day renowed for canals and aqueducts, to supervise the project. 

The upstart Stephenson treated Rennie with a cannily aggressive respect: the barrage of more than 82 letters that he sent to Rennie during the construction, dutifully requesting counsel and reporting on progress, served to keep Rennie usefully employed back in London, writing careful replies full of sage advice that Stephenson did not hesitate to ignore when it suited him.

Stephenson was also fortunate that Rennie suffered from seasickness; he visited the rock only twice during its construction. 

Bell Rock lighthouse cross-section. Credit: National Library of Scotland 

In planning the lighthouse, Stephenson and Rennie took note of the work of their engineering forebear, John Smeaton (1724–92). Stephenson based the initial design on Smeaton’s Eddystone Lighthouse (completed in 1759), which had a broad base tapering to a slender tower.

Smeaton had been inspired by the shape of an old oak tree that could withstand the storms that toppled less stable trees. Rennie’s experience now came into play, as he adapted Stephenson’s design for the rigorous conditions of the Bell Rock by insisting on a broader base and more gradual slope to deflect the battering forces of the waves.

Due to the violence of the sea and the surge of the tides, construction could proceed only in summer, when storms were less severe, and only during the few hours of low tides when the rock was exposed. If low tide was at night, the crew was expected to work by torchlight. 

During the earliest days of construction, the workers lived on a boat anchored off the reef. Later, they built barracks, perched on stilts next to the lighthouse and connected to it by a rope catwalk, where they lived in the middle of the stormy sea.

One young man who worked as a smith fell from the catwalk and was swept into the sea and drowned. He was the only fatality on the rock itself, although four men died in other incidents related to the lighthouse construction. 

While enduring gruelling weather and primitive living conditions, the men were engaged in hard labour and pushing the boundaries of engineering achievement. The foundations (which, due to the pitiless force of the sea, had to be extra deep) were hacked out of the rock with pickaxes. These required constant sharpening, so a forge was set up on the rock, where the smith was often working knee-deep in water.

Each of the 2,835 blocks of Aberdeen granite or sandstone had to be cut to precise dimensions. The work included the crucial dovetailing that would allow them to fit together in a minutely calculated, interlocking pattern of "courses". 

The finished stones were then loaded onto boats. Out at the rock, they were unloaded onto rails that encircles the tower, winched up into position by pulleys and secured with wooden wedges. Ninety courses of masonry took the tower to a height of just over 31 metres; with the addition of the glass light-room, the finished lighthouse topped out at 33.3 metres. 

The lightroom of the Bell Rock lighthouse. Illustration by R Lorimer. Credit: National library of Scotland 

The Bell Rock’s source of illumination was revolutionary for its era. Smeaton’s Eddystone Light had attempted to penetrate the infamous Scottish fogs with nothing more than a chandelier mounted with candles. 

For Bell Rock, Stephenson and his stepfather, Thomas Smith, a former lamplighter in Edinburgh, designed an apparatus of 24 silver-plated reflectors on a revolving frame, with panes of red glass fronting the reflectors on the two short sides.

Power to turn the frame was supplied by a drum wound with a weighted, descending rope. As the rope unwound, the drum turned. The resulting intermittently flashing red light became Bell Rock’s signature.

In February 1811, the first revolving light shone forth, visible for 35 miles. That original system operated for 30 years before the first upgrade, and the light has changed with technology several times since, being lit over the years by spermaceti (whale) oil, paraffin, diesel and acetylene gas.

Today, the light is powered by batteries charged by solarpanels, with generator backup, and is fully automated. The lighthouse was manned until 1988. 

Banner credit: John McMillan

Read more: 8 Best films about lighthouses 

Read more: Trapped under the North Sea

Keep up with the top stories from Reader's Digest by subscribing to our weekly newsletter