The Atlantic Rowing Race has begun from the Canary Islands after storms delayed the scheduled start on Sunday.
Cracknell and Fogle are among the two-man crews
A total of 26 teams are taking part in the non-stop 2,250-mile race from La Gomera to Antigua in the West Indies.
They include British Olympic rowing gold medallist James Cracknell partnered by TV presenter Ben Fogle.
New Zealanders Kevin Biggar and James Fitzgerald set the race record time of 40 days, five hours and 31 minutes in the 2003 event.
The world record for the route is 36 days and 59 minutes, set last year by the Devon quartet of Phil Langman Shaun Barker, Jason Hart and Yorkie Lomas.
The competitors, many of whom had little or no rowing experience, will spend up to two months at sea being battered by storms and living off ration pack food.
They are divided into solo rowers, pairs and fours.
Roz Savage, 37, from London, and Chris Martin, 24, from East Molesey, Surrey, will attempt the challenge alone.
Twenty teams of pairs are taking part, most of them British, but also including rowers from Denmark, the US and New Zealand.
Competitors Frank Bruno, 40, and Dominique Benassi, 44, from France, are the first amputees to attempt to row across an ocean.
Four teams of four, including two all-female crews, are also hoping to be first across the finish line in the Caribbean.
Martin Adkin, 19, from Beer, East Devon, who is in a team with his cousins Justin Adkin, 26, James Green, 24, and Robert Adkin, 23, is believed to be the youngest person to attempt the feat.