Several factors combine to make the passage around Cape Horn one of the most hazardous shipping routes in the world. The fierce sailing conditions prevalent in the Southern Ocean are challenging enough but combined with strong winds and currents in a more-or-less constant, west to east direction, large waves, icebergs, the extreme southern latitude of the Horn at 56° south, and the land itself with off-lying rocks were all natural hazards that made it little wonder it was referred to as "the sailors’ graveyard." There was also the added hazard of collision with other ships battling their way round in the days when ships often didn't carry lights and those they did inadequate in the murk and gales off Cape Stiff as it was often called by seamen. According to Villiers; From the time of its first rounding Cape Horn has taken its toll; in the history of the ship-of-sails it has claimed more victims than the break-up yards. As if the perils of the deep were not hazard enough, anyone with the misfortune to find themselves going ashore was considered, assuming they survived the rocks, to be in as much danger from the locals who, before the 20th century, were deemed distinctly unfriendly - even hungry!
Cape Horn is not part of mainland South America but is the southern point of Horn Island, the southernmost and one of the smaller islands in the Hermite group which, in turn, is to the south of the Tierra del Fuego archipelago. You'll have to take my word for it as much of this is not shown on the map at right! which is a detail from G.H.Swanston's Mercator Projection published in 1872 and thus more-or-less contemporary with Dum [b. 1879]. The navigable water between the south American continent and Antarctica is Drake Passage; Cape Horn marks its northern edge. The dividing line between the Atlantic and Pacific oceans is considered to run along the meridian of Cape Horn. Rounding the Horn essentially meant crossing 50° S twice; firstly, whether tackling the Horn from east or west, the 50th parallel had to be crossed in a southerly direction. Having passed Cape Horn itself, it was only when the 50th parallel had been cleared for the second time, going northwards, that navigators could consider the Horn to be behind them and another one in the eye for Davy Jones.
Cape Horn and Drake Passage is not the only option for sailing around the tip of South America. The Strait of Magellan, between the mainland and Tierra del Fuego, is a major albeit narrow passage which was in use for trade well before the route south of the Horn was fully exploited. The Beagle Channel, south of Tierra del Fuego, offers another possible, though difficult route; and there are various other passages around the Wollaston and Hermite Islands to the north of Cape Horn. All of these, however, are notorious for treacherous ‘williwaw’ winds, which can strike a vessel with great violence and little or no warning; given the narrowness of these routes, there is then a significant risk of being driven onto the rocks and into the arms of a local welcoming committee. The open waters of Drake Passage, south of Cape Horn, provides by far the widest route, about 400 miles (650 km) wide, with ample sea room for manoeuvring either beating to windward or as the wind shifted, and for this reason became the preferred route used by most ships, despite the possibility of extreme weather and wave conditions. A chart on the next page illustrates the space required when beating to windward round the Horn.
The climate in the region is generally cool, owing to the southern latitude. A study in 1882/3 found an annual rainfall of 53.42 inches, with an average annual temperature of 41.4°F (5.2°C). Modern records show that summer (Jan-Feb) average temperatures range from highs of 57°F (14°C) to lows of 42°F (5°C); in winter (July), average temperatures range from 40°F (4°C) to 29°F (-2°C). Wind conditions are generally severe, particularly in winter when visibility is often poor. In the same 1882/3 study, winds were reported to average 19 mph, with squalls of over 62 mph occurring in all seasons. So "cold, wet and windy" would be a decent odds-on bet for any forecast. Just how cold, windy and wet would depend on the season.
The prevailing winds in latitudes below 40° south blow from west to east around the world almost uninterrupted by land, giving rise to the ‘roaring forties’ and the even more wild ‘furious fifties’ and ‘screaming sixties’. These winds are sufficiently hazardous in themselves to suggest that ships traveling east should try to stay in the northern part of the forties (i.e. not far below 40° south latitude); however, rounding Cape Horn requires ships to press south of 56°, well into the zone of the fiercest winds. These winds are further exacerbated at the Horn by the funneling effect of the Andes and the Antarctic peninsula, which channel the winds as well as the water into the relatively narrow Drake Passage. Fierce wind is the norm, but abnormally fierce wind was also to be expected. Raging Cape Horn storms were jocularly referred to as ‘snorters’.
The strong winds of the Southern Ocean give rise to correspondingly large waves; these waves can attain enormous size as they roll around the Southern Ocean, as unimpeded by land as the wind. At the Horn itself, however, these waves encounter an area of shallow water to the south of the Horn, which has the effect of making the waves shorter and steeper, greatly increasing their danger. The water is additionally squeezed between the land masses of S. America and Antarctica in the same way as the wind. If the strong eastward current through the Drake Passage encounters an opposing east wind, this can have the effect of further building up the waves. In addition to these ‘normal’ waves, the area west of the Horn is particularly notorious for rogue waves, which can attain heights of up to 100 ft (30 ms).