Monday, 9 September 2013

Waratah - rogue wave.

At the outset of this blog I presented a theory explaining the loss of the Waratah. However, there are other possibilities which deserve our attention and thoughts. In this post I a focus on an entity known as rogue or freak waves. For  a long time these waves were regarded as myth, the product of an angry Poseidon, engulfing vulnerable vessels. However, in 1973, Professor Mallory, an oceanographer at the University of Cape Town, published a paper demonstrating that waves in excess of 20m in are possible along the Wild Coast of South Africa in exceptional circumstances.

A freak wave is a product of various forces.  A powerful (warm) current.  Strong counter winds (cold).  A narrow continental shelf. If we take a closer look at the route the Waratah followed along the Natal and then Wild Coast, our attention is drawn to the Agulhas current, which is powerful (up to 3 m/s), consistent (about 100 km wide) and warm (about 23 degrees centigrade in winter) relative to the surrounding ocean. It moves in a south westerly direction, demarcating the western boundary current of the Indian Ocean (from ~25°S to 40°S), and follows the edge of the continental shelf. The continental shelf is as wide as 40 km off the Kwazulu Natal coast, and as narrow as 10 km off the Wild Coast.

Frontal systems (winter phenomena) moving up the coast in the opposite direction propagate hurricane force winds blowing against the prevailing Agulhas current, thus generating large waves and deep troughs. If one takes into consideration the additional force created by the very narrow continental shelf off the Wild Coast, one has the makings of a so-called rogue wave which potentially can reach as high as 30m according to some sources and a trough so deep and menacing it has become known as a 'hole in the sea'.

If the Waratah was still on course as reported by the captain of the Clan Macintyre, 'upright and sailing rapidly ahead', she would have encountered the approaching frontal system and storm. Whether the Waratah experienced difficulties such as fire or not, encountering a rogue wave had the potential to engulf her as large as she was. She would either have been flipped over, or simply a catastrophic inundation of tons of water through the vast deck hatches would have taken the liner to a watery grave within minutes. Either option would account for very little flotsam.

If she had continued to float, inverted, with passengers and crew horrifyingly trapped within, she may have drifted out to sea beyond the shipping lane and beyond immediate discovery. Ultimately the force of sea pressure and a weakening hull structure would have allowed for ingress of water and eventually the Waratah would have gone down at a location probably beyond the continental shelf beyond any hope of discovery.

This theory would have thrown a line to the owners, Mr Lund and Co of the Blue Anchor Line, in that they could argue that there was nothing in effect wrong with the Waratah, and a freak of nature took her to the bottom - 'perils of the seas'. As it was, the Inquiry came to the conclusion the Waratah succumbed to the 'storm of exceptional violence', 28 July, 1909.

In conclusion, a rogue or freak wave would be a convenient explanation for the almost 'paranormal disappearance' of such a large steamship (500 ft). The following is an account which goes a long way to convince us that such sea conditions can bring the most illustrious of ocean going vessels to heel:

In 1962, The Edinburgh Castle (28 000 tons) was en route between Durban and East London. During the voyage the conditions at sea deteriorated.  Passengers reported in the evening that they felt the liner pitch steeply by the head.  This was followed by a terrifying shudder, almost as though the liner had run into a solid object.

What had in fact happened was the Edinburgh Castle sailed into one of the 'holes in the sea' mentioned above, and the corresponding 'freak' wave had broken over her bows onto the foredeck. The damage was extensive, from deck equipment to utterly destroyed horse boxes and shattered plate glass on the promenade deck resulting in flooding of the D deck.

Marco Polo (as mentioned in a previous post) had a similarly frightening encounter with an angry sea in 1996.

Cold Front - cold air mass moving up the coast meeting warm Agulhas current
                                                     

The Agulhas current depicted here as the relatively warmer tongue extending down the coast

freak wave in this graph is depicted by the sharp increase in amplitude relative to the norm

an image of approaching freak wave, horrifying for even the most hardened of seamen and women

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