A team of four men aged between 25 and 28 have set off from London's Tower Bridge on a 2,000-mile non-stop rowing race around Britain.
Totally unaided, the crew will face dangerous and fast turning tides and cross the world's busiest sea lanes, avoiding car ferries and industrial fishing trawlers.
The route is known as the world's toughest rowing challenge and more people have landed on the moon than completed it, organisers say.