Is the Core-loc the “best” unit for all applications?

The Core-loc presently represents an efficient use of concrete for breakwater armor units. This is due to an optimised packing density and in this sense it is the best unit. Some applications might require very large units (like cubes in excess of 100 t required at Sines, Portugal) or be prone to unsuitable or inappropriate construction conditions which would present practical limitations to the application of Core-loc. If you are unsure about the practicality of Core-loc for a specific application contact us with the project details for an assessment. 

Is it more important to achieve the correct armor unit placement for single layers compared to double layers?

Yes. While the concepts behind rubble mound breakwaters have essentially stayed the same over many years, advances in positioning and measurement instrumentation now enable much more effective control of placement and the recording of placed positions. It should also be borne in mind that fewer units need to be placed in a single layer compared to a double layer. More time can therefore be spent on ensuring the correct position of Core-locs without increasing the total construction time.

What are the advantages of using Core-loc?

  • A highly robust near zero maintenance armor layer with significant cost savings over other units.
  • Typically, a cost saving of between 20 and 40 percent in general compared to double layer units. 
  • Fewer units to be manufactured and stored (fewer moulds, less storage space required). 
  • Technical assistance from licensee (CLNA). 
  • Assistance with quality assurance and control.

How many breakwaters have been built with Core-loc units?

Approximately 19 breakwaters worldwide.

Does a single layer represent a higher risk of failure than double layers? 

No. If the same volume of concrete is used for a single layer than that proposed for a double layer, the single layer would be typically much more stable than the units in the double layer.

What are typical royalty charges? 

Royalty charges can best be explained by contacting the relevant licensees, in this case Core-loc North America (see contacts).

What quality assurance measures are provided? 

The established practical technical specifications provide the necessary backup for quality assurance. Experience with application of the Core-loc is shared between Core-loc projects and provides constant input into practical solutions to some of the challenges facing the application of single armor layer construction. The value of “having been there” goes a long way to ensure that quality can be achieved in a practical way. 

Who holds the Core-loc patent? 

The patent is held by the U.S. Army Corps of Engineers. Core-loc Africa holds the license for territories in Africa. Core-loc North America holds the license for the USA, Mexico and Canada. Both CLA and CLNA are associated with consulting engineers Prestedge Retief Dresner Wijnberg. 

What are the steps to be taken should I wish to use Core-loc? 

Contact CLNA with the following information: 

  • Location and purpose of structure
  • Water depth at toe of structure
  • Expected wave climate

CLNA will assist you with a preliminary unit sizing which can be used for costing purposes. If a decision is made to go ahead with a Core-loc structure a detailed design by a competent professional designer will be required. Scale hydraulic models are recommended as part of the detailed design. 

Where can I obtain Core-loc model units? 

A range of model units are retained by the Core-loc Licensor and Licensees of the various territories. Available units can generally be rented. New units can also be manufactured to exact standards within a relatively short time. Further information both for renting and manufacturing units can be provided on request. 

What are typical construction costs? 

It is difficult to give a general indication of costs. The size of the project, location and purpose can affect unit costs significantly. For
new breakwaters, the cost of quarry rock is likely to be more than the cost of concrete armor units. Typical construction costs based on previous projects can be provided where possible for new projects.

What support is provided by Core-loc North America? 

The following support is included as part of a standard license agreement: 

  • Preliminary design
  • Provision of standard technical specification
  • Quotes for manufacturing of moulds
  • Assistance with model tests
  • Assistance with evaluation of manufacturing and placing of Core-locs 

What requirements apply to specifying Core-locs in a tender document? 

CLNA needs to approve the preliminary and final design to ensure the appropriate application of the unit. The tender document should also make reference to the standard License Agreement setting out the basis for using the unit. It will be required that the owner or contractor responsible for the project construction enters into the sub-license agreement under which the units will be permitted to be manufactured. The contract needs to make allowance for this. A copy of the sub-license agreement is available on request. 

Who should I contact? 

Gordon Prestedge (

Anton Holtzhausen (