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A maintenance crew gets to work deep under the Channel, a team of teenagers braves the ultimate open water challenge, and a helicopter gets a little too close for comfort.

Trinity House is the organisation with the crucial task of maintaining lighthouses and buoys to help keep shipping safe in the Channel. Today's job is a particularly tricky one for the crew of the THV Patricia. Working in tandem with a helicopter crew, they need resupply the Wolf Rock lighthouse, 8 nautical miles off Land's End and marking an area of treacherous rocks. Landing a helicopter on board the ship in strong seas proves to be a hair-raising business.

Meanwhile a different kind of maintenance work is being carried out by another crew deep beneath the Channel. Since its opening in 1994, the Eurotunnel has carried nearly 364 million passengers. But after 20 years of service in a salty atmosphere, it needs regular maintenance to keep it running. The engineers have a short window of time to work late at night while the tunnel is shut - and with 24,000 volts of electricity to deal with 40 metres below the sea bed, it's a painstaking process.

Making their way through the Channel's chilly waters, a team of teenagers are attempting to swim the Channel to France. Regarded by many as the Everest of Swimming, the 21 mile crossing is one of the world's toughest challenges, featuring jellyfish, seasickness, choppy waters and a busy shipping lane. For the youngsters - the youngest of whom is just 13 - it's a mental as much as a physical challenge.