Monster wave becomes world famous

The monster wave that hit the Draupner E oil platform in the North Sea in 1995 quickly became world famous among oil industry scientists and wave researchers. Now the wave has had a resurgence, so to speak, and has become a hit among the general public, with more than 160,000 views on YouTube.

The BBC's video animation of the monster wave that hit Draupner E platform is a classic on YouTube, with more than 160,000 views. The monster wave measured 25.7 metres from top to bottom.

Monster waves - so called because their heights can top 30 metres - used to be something that only sailors talked about, if they managed to survive them. But when the Draupner E oil platform in the North Sea was hit by a nearly 26 meter high wave as recorded by instruments on the platform, scientists had to acknowledge that these monsters were real.

- Draupner E had only been out in the North Sea for a half-year when this huge wave struck the platform like a sledgehammer. When we saw the data, we thought at first it was a mistake,- says Per Sparrevik, leader of the Subsea Technology, Instrumentation and Monitoring discipline at the Norwegian Geotechnical Institute (NGI).

But the data were actually right: When NGI went through the information collected by its instruments and calculated the effect of the wave that hit the platform, the conclusion was clear: the New Year's wave that struck the unmanned Draupner E platform on 1 January 1995 really was extreme, and consequently has become one of the world's most famous waves, with 160,000 views of a video clip on YouTube. The monster wave came as a surprise to both the petroleum industry and wave scientists and triggered an extensive research effort, because it was so much larger than the waves that came before and after it.

The Draupner S oil platform (front), which includes living quarters, was installed in 1984. Draupner E is an unmanned platform that was installed in the summer of 1994. The platforms are located in the North Sea, midway between Norway and Scotland, and are a key hub in the North Sea gas pipeline network. (Photo: Statoil)

Before and after the Draupner event
Before the Draupner wave, researchers believed that the distribution of wave heights roughly followed the famous bell-shaped Gaussian curve, which would mean that such an extreme wave might occur every 1000 or 10 000 years. But when the Draupner E was hit by a nearly 26 meter high wave - a surprise in seas that otherwise featured significant wave heights of only 12 meters - the Gaussian theory was immediately refuted. A significant wave height is defined as the average of the highest third of waves over the course of 20 minutes.

- Subsequent research has confirmed that monster waves occur much more frequently than Gaussian theory would suggest, and wave researchers have therefore started to use what they call non-linear theories when they calculate wave heights,- says James Strout, PhD, who is director of NGI's Instrumentation and Monitoring Division.

An instrumented oil platform
The reason the New Year's wave was recorded at all was because Draupner E was the first major jacket-type oil platform in the world that was anchored to the seabed with bucket foundations instead of piles. A jacket-type oil platform is one where the structure has a fixed steel jacket. Bucket foundations and suction anchors were a new type of mooring that had previously only been used with smaller single point buoy moorings and anchors, but by the 1990s, the technology had been sufficiently proven that Statoil decided to use them on large structures, such as the Draupner E platform.

For safety purposes, the platform was equipped with a range of instruments that continuously checked to make certain that the bucket foundations remained in place during the worst winter storms. It was these instruments that for the first time ever documented that monster waves really exist. The greatest uncertainty was related to the platform settling into the seabed, or a so-called 'shake down' due to cyclical loading during storms.

The instruments on Draupner E measured wave heights, slope, subsidence, the pressure on the bucket foundations, tension in the legs and the acceleration of the deck and bucket foundations - and the monster wave was recorded by every sensor. Pressure gauges on the bucket foundations measured a large force that tried to pull the platform up on the side that faced the wave, while the corresponding instruments in the back of the platform recorded a great downward force. The accelerometers on deck and bucket foundations recorded a sudden movement, strong at the top and moderate on the bottom, and a laser-based wave height measurement confirmed that the platform's upper section had been hit by a gigantic wave.

But even though the waves were large, both the suction anchors and the platform maintained their position. Later calculations have shown that the suction anchors gave way about 10 mm horizontally and 5 mm vertically, which is well within acceptable limits. The bucket foundations could have tolerated significantly greater wave forces without letting go, and it's possible that the platform's steel structure would have collapsed before the platform itself was toppled.

Reliable technology
Monster waves most likely occur in storms where slow waves are overtaken by faster waves, which leads to a situation where the heights of the two waves are essentially added together. It is believed that monster waves are the reason behind numerous shipwrecks over the years, especially where ships have simply disappeared without having sent a distress call.

Oil workers at the Draupner complex did not notice anything special about the monster wave, because all work on deck had been stopped at 3 p.m. that day due to the storm. When the wave hit, the crews were all indoors on the adjacent platform Draupner S, which was sheltered behind Draupner E. There was some minor damage to the equipment on Draupner E's lowest deck, but that was all. Thus, the bucket foundations proved that this technology is reliable and can withstand extreme force.

Facts about Draupner E
 
The Draupner E is a jacket-type oil platform in 70 metres of water, far out in the North Sea between Norway and Scotland. The Draupner E and S platforms form a key hub in a North Sea gas pipeline network and are not drilling platforms.

NGI's assignment from Statoil for the Draupner field was to develop and design the bucket foundations, and to follow up on the platform's dedicated monitoring system. Statoil took responsibility for installing the bucket foundations. NGI was a member of a special 'task force' that was created to implement this pioneering effort, which was conducted from one of the world's largest crane vessels, the Saipem S7000.