Aubrey Kruger and the invention of the dolos

Updated: Jul 3, 2020

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. Yet the facts are somewhat different.

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.

East London draughtsman Aubrey Kruger with his invention.

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.