On 23 June 2008, the Suwa Maru No. 58, a fishing boat with 20 crew members, sank in seemingly moderate sea conditions of Cape Inubosaki, Japan.
Reports from the investigators indicated that although reported wave heights were between 2 and 3 meters (6.5 and 9.8 feet), the ship may have encountered abnormal waves twice, sinking the ship about 10 minutes after being hit by the initial wave.
Other possibilities, such as improper use of an anchor or an encounter with an unidentified submerged object, were suggested, but no definitive conclusion has been reached as to why the Suwa Maru sank. Noting that a number of ships have been wrecked in this region, which is notorious for abnormal waves, Tamura et al. seek to determine the state of the sea at the time of the shipwreck.
Using a hindcast wave simulation using a model driven by wind and ocean current, the authors find that at the time of the accident wave steepness increased and waves became long crested, creating a sea state favorable for freak wave occurrence.
Under the influence of rising wind speed, the swell system grew exponentially, dangerously churning the waters and creating a freakish sea state.
- Tamura et al. Freakish sea state and swell-windsea coupling: Numerical study of the Suwa-Maru incident. Geophysical Research Letters, 2009; 36 (1): L01607 DOI: 10.1029/2008GL036280
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