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Navy and science combine to map rogue waves

How do we know there are waves in the Southern Ocean four storeys high?

26 June, 2023

Media reports about ‘monster waves’ or ‘one-in-3000-year waves’ near New Zealand are drawing on the expertise of oceanographers and scientists. That includes the Defence Technology Agency, the main provider of research, science and technology support to the New Zealand Defence Force and the Ministry of Defence.

Since 2016, the Royal New Zealand Navy have supported DTA in its Southern Ocean wave observation programme, involving the deployment of wave buoys to measure wave height. During a mission to Campbell Island with HMNZS Canterbury in February, DTA deployed a wave buoy 20 nautical miles south of the island in 150-metre deep water.

The programme is best known for measuring the largest known wave in the Southern Hemisphere, a 23.8-metre “beastie” which developed during a storm in May 2018.

Doctor Peter McComb, DTA Trials Leader, says they are still analysing that event. “One of the characteristics that made that storm interesting was that it slowed down and allowed the wave energy to accumulate at this location.”

The information from the wave buoy programme has been crucial in the future design of ships designed for the Southern Ocean – where HMNZS Otago got hammered in 2016.

Previously, our ships have been designed to criteria dictated by Northern Hemisphere sea states.

“The Southern Ocean is characteristically different. There are no land masses in the way and there’s a huge westerly wind belt with rapidly moving low pressure systems embedded within it.

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DTA deployed a wave buoy from HMNZS Canterbury, 20 nautical miles south of the island in 150-metre deep water.

DTA believed that to design a ship specifically for the Southern Ocean it needed to be fit for purpose with the wave climate, but they need to start measuring Southern Hemisphere sea states, notes DTA Programme Leader Sally Garrett.

“Because we now have actual data we can accurately define how the wave conditions the ship will likely experience in the Southern Ocean are different to the Northern Hemisphere high latitudes.”

“Campbell Island is unique in that it provides some real estate that is very close to the energetic heart of the Southern Ocean. It’s right in that windbelt.”

“What we are trying to do is give the naval architects real wave energy spectra that ships will encounter.”

The buoy data is also used widely by the international science community for a wide range of studies, including an extensive project  that looks at how swells propagate across the entire Pacific Ocean, from the deep Southern Ocean all the way through to Hawaii. The Campbell Island buoy is the ‘ground zero’ location for that experiment. 

The latest buoy is also the first to be able to measure the current in the top 30m of water, which it does in 2m increments by an acoustic technique.