Double Olympic sailing champion Andrew 'Bart' Simpson, 36, had been sailing on the Artemis, Sweden's entry in the America's Cup, when the catamaran capsized, according to a statement for the team posted on the Artemis racing website.
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The popular game relies on Google Maps, a problem in South Korea as those functions are limited by the government.
A Met Office warning covering much of England and south-east Wales is expected to remain in place until 11am.
A band of cloud and patchy rain is expected across Scotland and Northern Ireland, moving southeast as the day progresses.