Aubrey Kruger and the invention of the dolos
Updated: Jul 3
This is about a South African invention that is still regarded as streets ahead of anything else devised for its purpose. But as is often the case in such matters, the person responsible for its development has not always received the credit deserved, which went to another.
We are talking about the dolos, those huge and oddly named concrete creations used to absorb and dissipate the energy of the seas, which are mostly found at the entrances to ports and harbours, although they also find use elsewhere where scour protection is required.
Up until the invention of the dolosse, large rocks and blocks of concrete were the most common means of providing protection against the notorious waves of South Africa’s eastern coastline. But even these massive and heavy objects could be washed away or moved about, and what was needed was something that was relatively inexpensive but would resist and reduce the force of the waves while remaining in position.
The man generally given most of the credit for inventing the dolos was a harbour engineer at the Port of East London named Eric Merrifield who served at the Eastern Cape port as the chief engineer from 1961-1976. Yet the facts are somewhat different.
Merrifield had little right to such a claim, other than that he was in charge of the engineering office at the time and had signing power for its development. It was, however, his request that set in motion the invention of something that has gone into use across the world as the most successful means ever of absorbing and controlling the energy produced by waves pounding away at natural or man-made areas of coastline.
Strangely, neither the inventor nor the port engineer sought to take out patents for what resulted from that request, although Merrifield was later to be granted, and he accepted, awards and recognition for which he was not really entitled. It appears that both men believed that, as they were employees of the state at the time, they were not entitled to reward for the invention.
One day in 1963 Merrifield entered into a discussion with his draughtsman about designing a structure made from concrete that would be capable of protecting the East London Harbour breakwater from the battering waves.
The draughtsman, 28-year old Aubrey Kruger, was a modest, quiet local man who rode to work every day on a red Vespa scooter from his home in Cambridge, one of East London’s suburbs. It was usual in those days at East London for people to return home at lunchtime each day and so, when Aubrey Kruger returned home by scooter that day the first thing he did was to commandeer his wife Daphne’s broomstick, from which he cut three pieces of wood which he nailed together in the shape of an H’ with one twisted leg.
His daughter Sandra says she can remember her mother being rather angry, and having to shoo a chicken out of the kitchen with a shortened broomstick. She says her father based his idea on the dubbeltjie thorn. After lunch he returned to work where he placed the wooden model on Merrifield’s desk.
The idea was that the dolosse, which would be cast in unreinforced concrete, would be placed in front of and on top of each other along the breakwater where they would interlock and, as waves broke against them, would fit even tighter while still allowing some of the waves to pass through the structures, thus weakening their force.
According to Sandra, the name dolos came from her grandfather, Joseph Kruger, who was a carpenter working at the harbour dry dock at the time. He saw his son and others in the office playing with small models and asked “Wat speel julle met die dolos?” - dolos being the Afrikaans for knucklebones often used by sangomas and herbal doctors when divining. Children also used to play with these knucklebones.
The Kruger family still has an original model of the dolos made by Aubrey using plaster of paris and left to dry in the garden. Aubrey Kruger’s son Lance retains this model in his possession.
The drawings for the first dolos were completed in 1963, based on the shape devised in wood by Aubrey Kruger. As port engineer Merrifield was responsible for overseeing the project and signing off all plans.
The following year, 1964, the first dolos was laid on the port breakwater.
Kruger enjoyed seeing the development of his invention which resulted in much excitement in the family. At the end of 1966 Kruger was transferred to Durban and was given a copy of the amendment to the design dated July 12, 1966 drawn by Aubrey Kruger and signed by Mr Merrifield, as a farewell gift from the East London office.
The family lived happily in Durban for seven years and it was only after the Shell Award was given to Merrifield in 1972 and a Gold Medal award by the Associated Science and Technology Societies of South Africa for the invention of the dolos that Kruger felt saddened by his not being mentioned for his part in the design.
Subsequent articles and reports written about the dolos and giving credit to Merrifield caused much pain and hurt to both Kruger and his family.
Kruger remained a man of few words who was never confrontational and preferred his own company, says his daughter Sandra. She says her father considered the invention to be the property of the South African Railways & Harbours (now Transnet) and would never have written papers about it, let alone have tried to have them published. “It was not in his nature to rock the boat,” she says.
Dolosse are in use across the world, either in their original shape or in variations but following similar principals. They can be found reinforcing the breakwaters of ports and harbours in the US, in South America, in Asia and in parts of Europe. There’s even one of many thousand at Port Ngqura festooned in the colours of the South African flag.
In 1973 Kruger and his family returned to East London where he left the employ of the SAR&H and started a tyre retreading company. He later sold the business and returned to work as a draughtsman for an architectural company and then as a truss designer for a timber company. In 1998 he retired on a state pension to a beach cottage and spent most of his time fishing and doing woodwork. Following a stroke in 2010 he and his wife moved to a flatlet on his son Lance’s property in the suburb of Vincent, East London.
On July 19 this year, two days before his 81st birthday, Aubrey Kruger died of cancer, being survived by his wife, Daphne, his children, Gary, Sandra, Ross and Lance, and six grandchildren and five great-grandchildren.
Not long before he died, his family was able to show him the newly minted sterling silver coins of a R2 crown and a 2½ cent “tickey” from the South African Mint in its South African Invention’s theme, imprinted with the geometric shape of the dolos, as well as three miniature silver dolosse by the South African Mint, which commemorated his involvement in the invention.