When the sea crashes over Port Taranaki’s Main Breakwater turning the air into a churn of white foam and salty mist, Rob Wilson feels a mix of excitement and apprehension.
“We’re a very exposed port here and have some pretty big seas. Sometimes you can’t see the breakwater with the amount of sea that’s flowing over it,” says the port’s civil works supervisor.
“It’s exciting, but the energy the sea produces is pretty incredible. These are 12 tonne and I’ve seen them picked up by the sea and tossed on the other side of the breakwater.”
The “these” he points to are the large concrete akmons placed along the breakwater to help protect the port from the strong West Coast sea conditions.
Like armoury for the breakwater, the concrete akmons are shaped so that the power of the sea moves them into positions where they interlock, while at the same time allowing enough space between each for the water to move freely. This helps break down the energy of the sea, enabling the harbour to be safe for ships to enter and exit.
Although the akmon was officially developed in the Netherlands in the early 1960s, stacked interlocking concrete blocks have been used to protect the port since the late 1800s.
Port Taranaki has always made its own akmons, with the port’s engineers settling on a design and size that suits the harsh conditions – a 12 tonne akmon for the Main Breakwater and a four tonne version for the Lee Breakwater.
Rob’s civil team has the annual job of making and replacing akmons that have deteriorated over time or been dragged to the sea floor by the waves. Each summer they pour and place up to 40, with six-monthly checks of the breakwaters carried out to determine if areas need to be bolstered.
During the years, akmon production has been rather nomadic – the team has had to shift sites as other port operations have taken over space.
But, thanks to the ingenuity of the civil team, they now have a permanent home, using a former rail load-off ledge near the neck of the Main Breakwater as the production base.
“The concrete bases that the steel akmon moulds fit over are set up under the edge, so the concrete truck can just back up and pour directly into the mould. Each 12 tonne mould takes a truck load of concrete, about 5m³,” says Rob.
“The guys have also modified a couple of the ‘grabs’ and one of the forklifts so that we can do all of the lifting of the akmons off the moulds ourselves. The process has saved time and money, doing away with hiring in cranes and concrete pumps.”
With another summer approaching, Rob says the team has been further finetuning the set-up as they work to make the port safe for all who use it.