The Magic of The Dolos & The Tetrapod
Just when you think you have the hang of the intricate lingo at the heart of the maritime industry, along comes something like the ‘dolos’ and the ‘tetrapod’. If you only have a passing knowledge of the shipping trade, you’d be forgiven for thinking that these terms describe particularly strange sea creatures, but in fact, it refers to rather complex concrete engineering structures that are designed to protect coastal spaces from erosion by reinforcing seawalls and breakwaters around harbours, etc.
The Difference Between a Dolos & a Tetrapod
First off, let’s clear this up. A dolos is a tetrapod, but a tetrapod is not necessarily a dolos – i.e. a dolos is one of the kinds of tetrapod that are constructed and used around the world. The reason why South Africans are more likely to refer to it as a dolos is that this was the name given to the particular structures that were invented by South African harbour draughtsman, Aubrey Kruger, in 1963 and first deployed on the breakwater of East London in 1964.
Although the exact shapes and weights of the concrete structures used for this purpose around the globe differ, they mostly share two characteristics – they feature four legs and have the ability to interlock in various ways. It’s this first characteristic that lies at the heart of the term ‘tetrapod’ (in Greek, ‘tetra’ means four, and ‘pod’ means legs).
The weight of the tetrapods used around the world tends to correlate with the weather conditions in each region. According to a study by Stephanie Wehkamp from Jacobs University, some tetrapods weigh as little as 6 tonnes each, while others can be as heavy as 30 tonnes (e.g. in areas like the north coast of Taiwan, where typhoons are common), even ranging up to 40 tonnes (e.g. in Libya, where these enormous structures safeguard the port of the economically important Misrata Steel Factory).
How Does It Work Though?
In simple terms, singular shape of these concrete structures breaks the force of incoming waves, while still allowing the water to flow around it. This, in turn, reduces displacement. Because these structures are so heavy, it remains in place through adverse weather conditions, offering a stable, yet porous, barrier that can withstand the power of wind, waves, and relentless currents.
Now you know! Keep an eye on the blog in the coming weeks and months for more interesting info on all things maritime. In the meantime, feel free to reach out to the Link Ship Chandlers team if you would like to find out more about our maritime supply services at Cape Town, Saldanha, Port Elizabeth, Coega, Durban and Richards Bay – our seasoned chandling teams are on hand to answer any questions you may have.