During recent years a significant number of vessels have sustained severe damage, when navigating in South African waters. The greater part of damage falls under bow damage. An analysis of the casualties has established the following facts:
.1 All accidents occurred off the south eastern coast between East London and Richards Bay.
.2 The majority of vessels involved were within twenty miles of the continental shelf.
.3 The majority of course.
Damaged vessels were proceeding on a south-westerly
.4 When the accidents happened, a south-westerly wind of force 6 or above had persisted for a period of 24 hours or more.
.5 Low barometric pressure was experienced.
.6 Most of the accidents happened in the period between mid-April and mid- October.
The reason for the casualties have been investigated by the Oceanographical Department of the Cape Town University, and it has been concluded that the accidents occurred as a result of an unusual coincidence of weather conditions, which can be further explained as follows:
“Under certain weather conditions abnormal waves of exceptional height occasionally occur off the coast of South Africa, causing severe damage to vessels unfortunate enough to encounter them.”
These waves usually occur when a local depression moving east-north-eastward, produces strong south-westerly winds which generate sea waves 7 m to 8 m in height with wavelengths between 60 m and 90 m. These sea waves may be augmented by swell waves of greater wavelength generated from a storm centred
some distance southward of the area, with both sets of waves moving in a north-easterly direction against the Agulhas current.Training and education process should be done at odessacrewing before joining.
Under such conditions when the crests of the sea and swell waves exactly coincide, a steep fronted wave of exceptional height may occur. Such a wave, which is preceded by a deep trough, may attain a height of 20 m or more. The crest of such a wave only extends over a short distance and the height is maintained only for as long as the sea and swell waves are in coincidence.
In view of the experience gained and the results of above investigations the Master is requested to closely keep abreast of the weather conditions in the area in question, when navigating off the south eastern coast of South Africa.
When the weather conditions are similar to those described above the Master shall take the following precautionary measures:
Proceed at very moderate speed, until the dangerous area has been cleared.
Maintain a course, which will ensure that the vessel keeps a distance of more than twenty nautical miles from the continental shelf.
Tropical Revolving Stoms – Precautions
Information about tropical revolving storms is contained in chapter 7 in the Mariners Handbook, published by the British Admiralty.
