The recent overflow of books on the so-called Bermuda Triangle has resulted in renewed interest in ship calamities, particularly those in which vessels are lost, apparently without a trace. However, increasingly better construction practices combined with improved weather forecasting techniques have reduced the number of unexplained ship losses in recent years. Improved data have, in fact, permitted the prudent mariner to become aware of some of the dangers of the sea which have always existed, but which have only recently been explainable. Among these phenomena are the fabled "monster waves” of yesteryear which, though they still pose a legitimate threat, can better be coped with through knowledge.
Seamen have long reported, along with sea monsters, huge waves of outlandish size. These waves usually appear during storms when the sea is already extremely rough. One wave suddenly will appear which will tower over the ones which preceded it. This article will offer an explanation for the existence of these waves.
On 27 March 1971, the tanker Texaco Oklahoma broke in two approximately 90 miles east of Cape Henry. Although the stern of the vessel remained afloat for some 36 hours, only 13 of the 44 people on board survived. Boards of inquiry subsequently conducted by the U. S. Coast Guard and the National Transportation Safety Board concluded that the Texaco Oklahoma had been in compliance with the inspection laws applicable to vessels of her class, and there was little reason to suspect substantial inherent structural failure to be the primary cause for the vessel’s loss. Admittedly, structural failure is what happened, but the boards found the failure to be related to the sea conditions which existed at the time. The weather was certainly unfavorable with winds in excess of 50 knots and seas of 25 feet, but other vessels of the Texaco Oklahoma's size survived that and other equally severe storms without breaking up. Could the possibility exist that one wave, of much greater height than those generally being encountered by the Texaco Oklahoma, either lifted her clear of the water so high that she pounded and broke, or else swept aboard and forced enough pressure admidships to rend her?
On 17 May 1974, the Norwegian tanker Wilstar was sailing southwest- ward near the east coast of southern Africa in the Agulhas Current. Her captain reported that he had observed waves striking the ship in series of sevens. At the end of one series, the seventh wave failed to materialize, and instead the ship lunged into an extremely deep trough which was followed by a wave much higher than the pre- ceeding seas. When this seventh wave crashed against the ship, it tore away the vessel’s bulbous bow and caused in excess of one million dollars damage.
Charts of the area in which the Wilstar lost her bow contain warnings to mariners that freak waves may be encountered. It should be noted that the Wilstar was operating east of (or outside) the 100-fathom curve at the time tragedy struck her. Fortunately, the vessel survived, but the question which must be asked (and more important, answered) is what caused such a wave?
Part of the problem, at least in the case of the Agulhas Current, is the fact that the bottom drops off rapidly beyond the 100-fathom curve. Additionally, the current which runs toward the southeast can be expected to cause sharper (steeper) waves when encountering a southwesterly wind than would be encountered during normal wind conditions. It is a simple matter of the air trying to push against the current and generating higher waves than normal.
Naturally, these same conditions could be expected to develop anywhere when a storm generates a wind-driven current in opposition to a sea current that already exists in the area. And here, perhaps, is where the Texaco Oklahoma reenters the picture.
The Texaco Oklahoma was encountering northeasterly winds just prior to her sinking. At the position where she is believed to have gone down (the exact location is unknown due to the ship’s inability to get off a distress signal before sinking and the extended period of time the survivors were adrift before being rescued) is in the Gulf Stream. When the Gulf Stream finally departs the U. S. east coast near Cape Hatteras, North Carolina, it assumes a northeasterly course and maintains a speed of from one to four knots. These conditions alone might well have been sufficient to cause a wave phenomenon, not unlike that encountered by the Wilstar, which could have broken the Texaco Oklahoma.
The Gulf Stream, however, has other influences which may contribute to the manufacture of freak (or monster) waves.
The so-called north wall of the Gulf Stream marks the northern boundary of that "river in the ocean,” and it is an area in which there is a rapid rise in temperature over a comparatively small geographical range. Particularly in the winter, when water temperatures in the North Atlantic drop, this change in water temperature can create unstable water conditions as well as unstable air masses in the atmosphere above it. Winter storms emerging from North America may move out over the water carrying cold air masses which eventually come in contact with the air being warmed by the Gulf Stream. The collision of these two air masses creates instability and may generate winds higher than those previously characteristic of the storms. In the past, in fact, forecasters have, on more than one occasion, found their estimates of winds contained in these outbreaking winter storms to be lower than those actually encountered.
Finally, the Gulf Stream roughly follows the 100-fathom curve in its move offshore, creating an additional disturbing influence on the normal movements of water. These factors (the Gulf Stream, the storms, and atmospheric instability) may then all combine to generate freak waves.
Yet, the problem compounds itself even further. First, all conditions must be right: i.e. a cold air mass encountering a warm mass which generates abnormally high winds; the collision of warm and cold water masses which create water instability, plus air instability in the surrounding atmosphere; the Gulf Stream generating its normal current of several knots; a northeasterly wind blowing against the Gulf Stream; and storm force winds whipping the sea into a frenzy. Such conditions can, by their very nature, exist in only a very limited section of the ocean where all these factors combine in one place and at one time. Thus, the forecaster has little way of knowing if all the factors will be present to create the freak waves, and perhaps the only way he will find out is if such waves are reported.
It should be obvious then, that if freak waves are, in fact, generated by early spring storms moving off the coast, they should be encountered more frequently during such storms. The Texaco Oklahoma was lost in a March storm. The bulk carriers Anita and Norse Variant, both in excess of 450 feet in length and 12,000-ton displacements, were both lost in a storm during the month of March in 1973. Only one survivor from the Norse Variant was recovered and none were found from the Anita. Certainly the losses of such vessels, all during the early spring, during storms with strong northeasterly winds, and in the vicinity of the north wall of the Gulf Stream, would lend credence to the monster wave theory and how these waves develop.
As with most dangers, some knowledge of the problem is at least a step in the direction of solution. It is unlikely that man will ever be able to control the sea, but by knowing that such phenomena as freak waves exist in more than just "sea stories,” seamen may better be able to cope with them.