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MERRIFIELD, Eric Mowbray

Born: 1914 03 20
Died: 1982 12 01



Eric Mowbray Merrifield was the System Harbour Engineer of the Port of East London from 1st September, 1961 until his retirement in 1976. He is notable for the invention and development of the Dolos, an armour block used in breakwaters, groynes and harbour walls to dissipate the immense energy of waves, maintaining the integrity of the structures.

Eric Mowbray Merrifield was born on 20th March, 1914 in Eldorado, Southern Rhodesia (now Zimbabwe), the first son and eldest of four children to John Mowbray and Margaret Louise Merrifield, who had separately immigrated from the UK, marrying in Eldorado where John Mowbray was working as a mining engineer.

The family moved to the Witwatersrand where John Mowbray was employed on the Rose Deep gold mine. Eric was schooled at Ridge Preparatory School in Johannesburg and subsequently at St Andrews College in Grahamstown where he matriculated. Returning to Johannesburg he was awarded the degree B.Sc in civil engineering in 1937 by the University of the Witwatersrand.

On graduating Eric Merrifield joined the South African Railways and Harbours Administration and was posted to Cathcart in the Eastern Cape/Border area. On June 10, 1940 he married Mary Bertha Hoffman (1912-1971), in Cathcart where Mary was born, and had grown up in a large Austrian immigrant family. Mary studied nursing at the Frere Hospital, East London and the Frontier Hospital, Queenstown and became a mid-wife in Queenstown where she worked in the African hospital. Later, in the 1950s and early 1960s when living in Cape Town, she continued to nurse the underprivileged, in particular babies suffering from severe gastro enteritis, working as a volunteer in the clinics in Retreat and Grassy Park in the Cape Peninsula.

Working for the South African Railways and Harbours Administration Eric Mowbray was relocated to Upington in the NW Cape, where his elder son Robin Mowbray was born.

He was again relocated to South West Africa (now Namibia) to be part of the new railway line survey and construction team.

In 1947 he was transferred to the Cape assuming the duties of District Harbour Engineer, SAR&H, a post he held for many years. He was also responsible for the small harbours on the Cape west and southern coast. In 1948 his second son Caesar Mowbray was born in Cape Town.

He was known as being fair to all and a sincere supporter of the ordinary worker who he always treated with great respect. He had an old fashioned respect for all people – a valued characteristic in those difficult times in South Africa. One thing that touched him deeply when he departed Cape Town for East London was being presented, in the Cape Town harbour, with a beautiful traditional clay model of a large bull with magnificent horns by the chief representative of the African work force. The workforce had regarded him as a sincere leader and a champion of their aspirations.

He was one of the first civil engineers in SA to become registered as a professional engineer (PrEng) and he worked tirelessly to promote engineering to young people and the public at large. He also had an abiding love for the theatre and acting, appearing as a semi-professional in radio plays and as an amateur on stage in both Cape Town (Masque Theatre, Little Theatre) and later in East London (Guild Theatre).

In 1961 he took up the post of System Harbour Engineer, East London.

It should be noted that East London is South Africa’s largest commercial river port with its associated challenges. It was during the early 60s that the story of the Dolos unfolded. Faced with having to maintain harbour protection, particularly protection of the Western Wall, from the storms from the Indian Ocean and the continuous destruction of the harbour breakwater Eric Merrifield saw the necessity of developing an innovative method of preserving the integrity of the breakwater whilst effectively dissipating the energy of the waves. The traditional use of rectangular concrete breakwater blocks having masses of 20 Tonnes or more was proving ineffectual with many being washed away by the waves. Eric Merrifield believed that an interlocking block, similar to the existing Akmon and Tetrapod blocks would be the only way to dissipate the wave energy and to prevent the blocks from being displaced.

It was at this time that Eric Merrifield invented the Dolos, a block which approximated the general shape of an Admiralty sea anchor [see photograph bottom right] and which would naturally interlock whilst acting as a group and would also effectively dissipate wave energy. The idea of this shape came to him whilst he was working in Cape Town and had to devise a way of retrieving sea anchors after a small boat sank in the dock with a number of these on board. They had interlocked and had to be cut up to reduce their weight prior to raising. It struck Eric Merrifield that a breakwater block of similar shape might behave in a similar fashion. This resulted in the idea of a block shaped as the letter H with the legs rotated by 90 degrees.

Small simple proving models (100mm size) were manufactured initially by a talented carpenter on his staff and these were subjected to preliminary stability checks. It was at this time that the carpenter posed the question "En wat gaan meneer met hierdie dolos maak?" [What are you going to do with this dolos?] – a dolos being the Afrikaans for the knuckle bone in a domestic animal's leg and which was used by a sangoma in the diagnosis of ailments – and by children in rural games. Thus was born the name "Dolos (plural Dolosse)".

The development of the Dolos then took off in earnest in conjunction with local SAR&H technical staff and with the CSIR coastal research station in Stellenbosch. This saw the emergence of a world acclaimed breakwater block. It was subjected to a multitude of physical tests and mathematical modelling to establish its stability, hydraulic effectiveness and its ease of manufacture. Eric Merrifield worked closely with Dr J Zwamborn of the CSIR, evaluating test results and checking these against mathematical models which were devised to validate the Dolos performance. Initially the Dolos was designed so that its structure required no internal steel reinforcement. This reduced the cost and the propensity for it to corrode in the sea water. In later years some designs included internal steel reinforcement.

Working for the SAR&H and wanting engineers worldwide and society in general to benefit from this invention, both he and the SAR&H decided that the design was never to be patented. This resulted in worldwide use of the Dolos and acclaim for both Eric Merrifield and South African engineering. However, he was, inevitably, commissioned by many coastal and harbour authorities internationally to advise on the construction and application of the Dolos in their projects. As a consequence he travelled extensively to countries such as Japan (where he presented a paper as an invited speaker to the 10th international conference on coastal engineering, introducing the Dolos to the international community for the first time), the USA where he gave the keynote address at a world nuclear conference. He also acted as a consultant to the US Corp of Engineers developing Dolos protection for Humboldt harbour, USA, and in other locations including Hong Kong High Island Scheme, Australia, Cabinda and Denmark where he was awarded the freedom of the city of Esbjerg. He was commissioned by the British government to assist the authorities in Tristan da Cunha to rebuild their harbour following the volcanic eruption in 1961, requiring him to spend some time on the island. He was awarded the Shell Design Award in 1972 and the Gold Medal of the National Science Technology Forum of SA in 1975. In his retirement he travelled to the UK and addressed a conference at HR, Wallingford - an internationally renowned independent Civil Engineering and Environmental Hydraulics organisation (which started in 1947 as the Hydraulics Research Organisation of the UK's Department of Scientific and Industrial Research)

Eric Merrifield was a complex man, an inventor, a practical engineer, a naturalist, an artist, a good father. He had boundless energy and an enquiring mind to go with it. He was an accomplished engineering mathematician, turning an intuitive idea of the Dolos into a mathematically justifiable solution to wave energy dissipation. Whilst being completely comfortable with engineers at the forefront of the science of harbour engineering internationally he also enjoyed the company of the common man.

Eric Merrifield died in East London on 1st December 1982 and was cremated and his ashes scattered over the dolosse on the East London breakwater, during a small family ceremony.

In 1997 he was honoured by having his name adopted for an innovative and academically excellent school in East London. Merrifield Preparatory School and College promoting innovation, diversity and excellence was established, named after Eric Merrifield commemorating the development of the world famous Dolos.

Compiled and submitted by:

Robin Mowbray Merrifield and Caesar Mowbray Merrifield, February 2019

Selected publications by Eric Merrifield relating to the Dolos

Merrifield E.M. & Zwamborn J.A., (1966) "The economic value of a new breakwater unit 'Dolos'", Proceedings of the 10th International Conference on Coastal Engineering, Tokyo, Japan, 1966, Publ. ASCE.

Merrifield E.M. (1968) "Dolos concrete armour protection", Civil Engineering Publication, ASCE, December, 1968.

Merrifield E.M. (1969) "The manufacture and placing of Dolosse", Guidance to Clients and Contractors – Publication through the SAR&H Administration.

Merrifield E.M. (1970) "The Dolos", The Civil Engineering Contractor, April, 1970.

Merrifield E.M. (1970) "Dolos – a new breakwater and coastal protection block"., Dock and Harbour Authority Journal, July, 1970.

Merrifield E.M. (1971) "Taming the Waves", The South African Engineer, June, 1971.

Merrifield E.M. (1977) "Rubble mound breakwaters – The state of the art", Dock and Harbour Authority:- A technical comment on the Proceedings of the Isle of Wight Conference pertaining to Dolosse. Aug, 1977.

Selected publications by others relating to the Dolos.

Hudson R.Y. (1961) "Wave forces on rubble mound breakwaters and jetties". Misc. paper NO 2-453, US Army Engineers, Waterways Experiment Station, Vicksburg. September, 1961.

CSIR Contract Report (1965) "An investigation into the merits of the new 'Dolos' breakwater armour unit". National Mechanical Engineering Research Institute, Report MEC 391, CSIR, Pretoria, September, 1965.

Magoon O. & Shimizu N., (1970) "Use of Dolos Armor Units in rubble-mound structures eg. For use in the Arctic" Corps of Engineers, US Army, San Francisco, USA.

Wallingford H. R. (1970), "High Island water scheme – Hong Kong – A study on the use of Dolos armour units for wave protection on the seaward face of the Eastern Dam". Report EX532, October, 1970.

Zwamborn J.A. & Beute J. (1972) "Stability of Dolos Armour Units". Proceedings of the ECOR Symposium on 'The challenge to the South African Engineer'. Johannesburg, November, 1972.

Burcharth H.F., Brorsen M. & Larsen T. (1973), "Stabilitet af Dolosskraninger", Bulletin No.3, ex Laboratoriet for Hydraulic og Havnebygning, Aalberg, Denmark, March, 1973.

Daffy J. (1974) "Technical report on breakwater units", Cement and concrete association, Australia, September, 1973.

Hudson R.Y.(ed) (1974), "Concrete armor units for protection against wave attack", Report of Ad Hoc Committee on artificial armor units for coastal structures, U.S. Army Engineer Waterways Experiment Station, Vicksburg, USA, January, 1974.

Paolla G. (1978) "Impiego dei Dolos per il porto Oceanico di Sines in Portugallo". Società Italiana per Condotte D'acqua Report, February, 1978.

Carver D. & Davidson D.D. (1997) "Dolos armor units used on rubble-mound breakwater trunks subjected to non-breaking waves with no overtopping". Report H-77-19, Army Engineer Waterways Experiment Station, Vicksburg, USA, November, 1997.

Bowen D (1998), "The history of the Dolos", Coelacanth, Journal of the Border Historical Society Vol. 36, No.2, December, 1998.

Zwamborn J.A., Bosman D.E. & Moes J. (1980) "Dolosse - past, present, future?", Proceedings of the 17th Conference on Coastal Engineering, Sydney, Australia, pp 1948-1967.

Silva E.N. & Foster D.N. (1974) "Dolos as an armour unit in breakwater construction", Fifth Australian Conference on Hydraulics and Fluid Dynamics, University of Canterbury, Christchurch, New Zealand.

Tulsi K. & Phelp D. (2009) "Monitoring and maintenance of breakwaters which protect port entrances", Proceedings of the 28th Southern African Transport Conference (SATC 2009), Pretoria, South Africa, 317-325.


The History of the Dolos by David Bowen.

Dolos concrete armor protection. Eric M. Merrifield. Civil Engineering - ASCE, December 1968. pp 38-41

Dolos - A new breakwater and coastal protection block by Eric M. Merrifield

The Dolos by Eric M. Merrifield. The Civil Engineering Contractor - April, 1970. pp 18-25

The economic value of a new breakwater armour unit 'Dolos'. E.M. Merrifield and J.A. Zwamborn. Proceedings of the Conference on Coastal Engineering, Tokyo, Japan. September, 1966

Dolosse for Coastal Works by J.A. Zwamborn. Paper presented at the SAICE Regional Convention held at the University of Stellenbosch 28-30 September 1976

Dolosse - past, present, future? by Zwamborn J.A., Bosman D.E. & Moes J. 1980

Dolosse - past, present, future? by Zwamborn J.A., Bosman D.E. & Moes J. 1980

Celebrating century milestone of Merrifield’s namesake Merrifield Preparatory School and College Newsletter.

All information and photographs submitted by William MARTINSON.

See also:
Dolos Breakwater Block Memorial, East London Harbour
Dolos Casting Yard, East London Harbour

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