Canadian Historic Sites: Occasional Papers in Archaeology and History No. 9
by Edward F. Bush
Basic Principles of Lighthouse Design and Location
Lighthouses may be broadly defined under two heads: wave-swept and land structures. Although the latter may frequently be found in exposed locations, in general the wave-swept tower offers the greatest challenge to designer and builder alike. There are four kinds of construction used in wave-swept towers at present: (1) masonry and concrete, (2) cast-iron plated, (3) caisson foundation and (4) openwork steel. Masonry and concrete construction is preferred at sites where stone or brick is costly to transport. The openwork steel tower is resorted to on shoals, coral reefs or sandbanks in which a secure foundation is to be had only by means of steel piles driven deep where excavation is impractical. Likewise, the caisson foundation often is recommended at such locations.1 Figure 2 illustrates basic types of construction currently in use.
Lighthouses may also be functionally categorized under four general heads: (1) landfall lights, (2) major coastal lights, (3) secondary coastal lights and (4) harbour lights. Landfall lighthouses are located on shipping approaches generally well offshore to serve as the first landfall for inbound shipping and to provide a first bearing for outbound shipping. As one would suppose, landfall lighthouses are equipped with the most powerful lights available. Examples of several well-known landfall lighthouses are Bishop's Rock off the Scilly Isles (the first sight of the approaching English coast on a course for the Channel), and nearer home, Cape Race and Belle Isle, from which eastbound shipping out of the St. Lawrence takes its departure. Next in importance are the major coastal lights on the approaches to major ports or at the mouths of principal rivers. The Sambro Island lighthouse on the outer approaches to the port of Halifax and the oldest surviving lighthouse in Canada is an example in this category, as is Prince Shoal at the confluence of the Saguenay and St. Lawrence rivers. These two are fitted with powerful lights, although generally not to the same extent as the landfall lights. Secondary coastal and harbour installations exhibit lights of decreasing power and intensity; the latter, many of which may aptly be described as shaped like a pepper-shaker 10 or 15 feet in height, are often to be found at the head of piers or jetties.
Wave-swept lighthouse towers are usually of tapering circular design and are frequently set upon square foundations. Land-based lighthouses, by contrast, come in all shapes and sizes. Briefly they may be broken down into three broad types: (1) towers solely, (2) towers with attached dwellings and (3) houses with short towers, cupolas on the roof, or simply exhibiting the light from a window. Simple mast and pole lights are frequently seen on inland waterways other than those of such expanse as the Great Lakes. Towers are in a variety of shapes, circular, hexagonal and octagonal being the most common.
The range of a light; that is, the distance at which it can be seen in clear weather, is computed in nautical miles and is dependent on two factors; the height of the light above the water, governing what is termed its "geographic range," and the intensity of the light computed in candela (an internationally recognized unit of luminous intensity equivalent to a British standard candle), called its "luminous range." In the case of major lights of high intensity the range is limited only by the curvature of the earthhence range varies directly with the elevation of the light. Atmospheric conditions such as fog, rain, snow or haze greatly reduce the range of all lights.2 Landfall lights are installed in towers up to 200 feet in height (often, though not invariably, the distance between high water and the focal plane of the light) with ranges of from 20 to as high as 25 nautical miles. Major coastal lights rarely exceed 150 feet.
The height of a lighthouse tower is determined by its location. In general, tall towers are called for on low-lying shores or offshore rocks in order to gain the maximum range. On the other hand, lighthouses built on lofty promontories often call for squat towers, for if at a high elevation the light might too frequently be obscured by fog.
In choosing a lighthouse site an area subject to rapid coastal erosion should be avoided. Many a sturdily built lighthouse has been undermined by this process, necessitating removal to a safer location. Sable Island, with the unenviable title "the graveyard of the Atlantic," is a notorious example of the effect of coastal erosion, and another is Long Point on Lake Erie. The opposite phenomenon is coastal accretion, brought about by offshore currents or river estuaries dumping deposits in such amounts that the shoreline advances, thereby reducing a lighthouse's effectiveness.
Another basic factor fundamental to the very purpose of a lighthouse was under debate in the early 19th century: Should a light serve to warn the mariner to keep well clear or encourage him to approach the location? A case in point again is Sable Island. on which many a ship had foundered. As early as 1801, two lighthouses were recommended for this location, one at either end of the treacherous crescent-shaped isle, to be located as near the hazardous sandbars as possible.3 Nothing was done, however, other than the establishment of a rescue station. More than 30 years later, Francis (later Sir Francis) Beaufort, a celebrated naval hydrographer, condemned the project in his "Report on the several documents relating to the Lighthouses of the British Colonies in North America."
Another 38 years were to pass before the Department of Marine took the long-deferred project in hand and put the first pair of lighthouses in service in 1873. By that time, lights of such sufficient power were available that Francis Beaufort's objections were no longer tenable. Today lights serve both functions, depending on the location and hazards involved.
British Structural Design
The 18th century is noteworthy for the remarkable progress made in lighthouse construction and the beginnings of greatly improved lighting apparatus. Nowhere was this more apparent than in the British Isles, France and Sweden.
English architects pioneered the challenging design and construction of the first wave-swept towers, structures exposed, generally on rocks offshore, to the full onslaught of the sea. The first of these was the Eddystone light, 14 miles off Plymouth and open to the broad Atlantic. Henry Winstanley built the first Eddystone lighthouse, an elaborate tower in the Baroque tradition featuring galleries and projections. Completed in 1697, it was swept away by an unprecedentedly fierce storm on 26 November 1703. John Rudyerd, a silk mercer of London, assisted by two expert shipwrights completed the second lighthouse on the Eddystone Rocks in 1709. Although sturdily built of bolted and clamped oak timbers, this second structure fell victim to fire in 1775. The third lighthouse, built by John Smeaton between 1756 and 1759, subsequently was condemned due to subsidence of its foundation. The fourth and present Eddystone lighthouse, 133 feet in height, was completed by J. N. Douglass in 1882.
The most difficult project of all fell to a Scottish engineer, R. Stevenson, grandfather of the talented novelist and poet Robert Louis Stevenson. The construction site chosen for the Bell Rock lighthouse consisted of rocks 12 miles off the east coast of Scotland. The site was a peculiarly hazardous one because the foundation work was below high water. This well-known offshore light was completed in 1811. Yet another notable achievement was the building of the Skerryvore lighthouse off the Isle of Tiree, on the mountainous and irregular west coast of Scotland. The Skerryvore light, 158 feet in height, was completed in 1844. These exposed towers required a high measure of skilled design on the part of the engineer or architect, implemented by rugged masonry.5
As steam replaced sail on the high seas during the rapidly industrializing 19th century, many waveswept lighthouses were built at exposed sites in various parts of the world, Horsburgh, Singapore in 1851: Minot Ledge, Massachusetts in 1860; Alguada Reef, Andaman Sea in 1865, and Great Basses, Ceylon in 1873 are but a few.6
Canadian Tower Construction
Although the two earliest Canadian lighthouses, Louisbourg and Sambro Island, were very solidly built masonry structures, this was not to be the invariable pattern for the future. The British North American colonies were bound by the limitations of a more stringent purse than either the United States or Great Britain. In the case, for instance, of the two St. Paul Island lighthouses built in 1831 and 1839, the Elder Brethren of Trinity House in London strongly recommended stone construction and dioptric apparatus; the Nova Scotia lighthouse commissioners on the other hand, opted for wooden towers fitted with catoptric apparatus. This decision was not solely based on economy; the governor made known in a despatch to the colonial secretary on 23 March 1838 that to proceed otherwise would have resulted in considerable delay.7
Wood, although less durable than masonry, was frequently preferred in Canada due to its abundance. The New Brunswick lighthouse commissioners, for example, showed a preference for wood or frame construction for this reason. Normally one would not expect a frame tower to be as durable as a masonry structure, although a number of timber and frame lighthouses have in fact stood the test of time. One of these is the Gannet Rock lighthouse, a rock station 7 miles off the southern tip of Grand Manan Island. This lighthouse, built in 1831 and, apart from the lantern, still in its original state today, was the object of critical remarks on the part of the master of HM sloop Persian in 1851. A New Brunswick lighthouse commissioner's defence of the structure has been borne out surely by the test of time.
Many circular cast-iron lighthouse towers were built along the shores of Newfoundland and were the subject of much dispute. The imperial authorities (Board of Trade and the Admiralty) who built the majority of the more important lighthouses in Newfoundland favoured this type of construction.9 A typical structure of this type is shown in Figure 31. Local authorities frequently took issue with this imperial predilection for iron towers. Robert Oke, a celebrated Newfoundland lighthouse authority, in his report for 1856 inveighed against the unsuitability of iron towers in so damp a climate. A case in point was Cape Race tower; condensation and hoarfrost on the interior walls had made the living quarters uninhabitable. A marginal notation within the report indicates that the Board of Trade had been warned of this possibility beforehand.10 A visiting Canadian engineer. G. F. Baillarge, supported this contention on a visit to Newfoundland nearly 10 years later.11 Sir Alexander Bannerman, the lieutenant governor, made the same point in a despatch of 22 December 1857, contending that brick was the most suitable material for use in Newfoundland.12
Iron towers found favour because of the very little maintenance required compared with brick and masonry. In 1878, the Newfoundland inspector of lighthouses and public buildings strongly recommended an iron tower for the projected Cabot Island lighthouse. Brick and stone required annual maintenance, even in the case of the best materials, whereas iron required but a little paint to counteract corrosion.13 The subject remained a debatable one in Newfoundland.
John Page, Canadian chief engineer, in his report for 1859, favoured stone work to brick for exterior surfaces. Brick did not lend itself so well to circular construction. Wood, brick and stone had all been used in lighthouse construction throughout British North America, wood being the most prevalent, particularly on inland waters. The wooden St. Paul Island lighthouses had withstood the ravages of wind and weather in that stormy location for the previous 20 years. Page completed his observations with the conclusion that the objection to iron towers was the danger of instability, and that mode of construction should only be resorted to at sites where stone and brick were not available and costly to transport from a distance. The soundest tower design was to be found in France, in which an insulating air space was left between the inner and outer walls to counteract the deleterious effect of dampness. Only stone of uniform grain should be used; generally speaking in Canada granite and limestone were most satisfactory.14 Reinforced concrete and steel, available in the early years of the 20th century, were to add a new dimension to lighthouse design.
The Canadian engineer previously cited, G. F. Baillarge, found that American pressed brick lined inside and out with Portland cement was a frequently used alternative to the cast-iron tower in Newfoundland. This combination proved moisture-resistant to a high degree, a prime requisite in a climate as damp as that of Newfoundland. Based on a stone foundation, this type of construction frequently was combined with three or four courses of freestone at the topmost levels, ostensibly the better to withstand the effects of weathering in windswept locations. The freestone was brought in from Wallace, Nova Scotia, priced at 30 to 60 cents per cubic foot. The Boston region supplied the American pressed brick at $7 per thousand.15
The Department of Public Works records offer considerable construction detail on the Cape Jourimain lighthouse (Cape Tormentine) completed in 1870. This is worth citing, not because there was anything unusual about this tower but rather because it was representative of the period. It was a timber and frame eight-sided tower 51 feet in height, the sloping sides tapered from a 20-foot length at base to 9 feet at the top. There were four storeys including the lantern room. The joists at ground level and the first storey were 13 inches deep and 4 inches thick. The sides, floor and hatchway of the lantern were sheathed in galvanized iron as a fire preventive. From ground level to the lantern platform the tower was covered with high-quality shingling, and above this level with galvanized iron. The cost of construction, including a dwelling, was $2,974. The light was ready for service by 5 January 1870.16
A perusal of the Admiralty light lists compiled in 1884 covering the coasts and inland waters of British North America indicates that lighthouse towers generally followed a circular, square or octagonal design.17 The tabular statement of lighthouses for the (pre-Confederation) Province of Canada on the eve of the federal union lists square frame and stone towers as recurrent types in what were shortly to become the provinces of Quebec and Ontario. Brick was not in common use in this region. Hexagonal and octagonal towers were not uncommon with one light at Coteau-du-Lac described as "on top of a house."18
The new century, which has so featured accelerating technological change, gave early confirmation of this trend both in lighthouse construction and apparatus. Reinforced concrete and steel skeleton towers made their appearance in the early years of the 20th century. The tower installed at the north end of Belle Isle in 1908, which went into service the following spring, was a cast-iron structure built in sections by the Montreal firm of H. R. Ives. A coat of reinforced concrete was applied a few years later, the whole supported by buttresses resting on rock.19
An early forerunner of the now familiar skeleton steel tower was ordered by the Department of Public Works for the north pier at Kincardine, Ontario, in the spring of 1903.20 Point-au-Baril lighthouse on Georgian Bay (Lake Huron) was of similar design, and was installed the same season. As with most towers of this type, these were square with sloping sides imparting a tapering shape to the whole. The Varennes light in Quebec was a third early installation. Both reinforced concrete and skeleton steel towers had won general acceptance and were to be found at a number of locations by 1917.21
Sable Island posed a challenging site for lighthouse construction. In an utterly exposed location far out in the Atlantic, the desolate and notorious island, by reason of its continually eroding and shifting sands, never allowed for permanence of installation. The first pair of lighthouses, wooden structures at either end of the crescent-shaped island, date from 1873. A lighthouse of skeleton steel design was installed in 1917. Built by the Dominion Bridge Company in Lachine, the tower was shipped in sections to Dartmouth at a total cost (fob) of $3,836. An individual foundation for each of the four legs of the tower was provided to a depth of seven to eight feet, in order to cope with the ceaseless undercutting of the sand by the wind. Re-assembled on the site, the work was completed and the light in operation by 18 December 1917.22 Only nine years later, the corrosive action of the salt air had had its effect on parts of the tower. In 1935 a concrete tower was recommended for Sable Island on the grounds of steel's rapid corrosion at such a location. Nonetheless. a decision in May of the same year again favoured open-work steel construction, still in use today at the site.
A cast-iron cylindrical tower was designed and built at the Prescott depot, complete with lantern and optical apparatus, for assembly at Cape Norman in the Strait of Belle Isle in 1906. Cape Bauld, in the same region on the northern coast of Newfoundland, was being provided for in similar manner the same year.23 These two installations featured the long familiar circular cast-iron construction but were of Canadian manufacture.
Post-1945 tower construction felt the rapid winds of change. In 1952 an offshore lighthouse, the foundation for which was a cellular crib of reinforced concrete built in the Sault Ste. Marie drydock and towed to the site, replaced the lightship on Gros Cap Reef, Lake Superior. On the cribwork filled with concrete, whose prow-shaped foundation was especially designed to withstand ice pressure, rested a lighthouse, fog alarm and radio. This offshore installation resembles the forepeak and bridge of a lake freighter.24
The White Island Shoal lighthouse, replacing a lightship in Lake Superior in 1955, and the Prince Shoal lighthouse on the lower St. Lawrence are of similar design. The foundation consists of a steel pier in the form of a cone on which rests an inverted cone of similar dimensions, its top thus providing a circular flight deck for the reception of helicopters as well as a base for the light and radio installations.25