Chris Thrall and Louie Greenhalgh started the 3,000-mile journey on December 8, which requires 14 hours of rowing every day.
The trip should take them up to three months.
The row is being led by Chris, 54, a former Royal Marines Commando from Plymouth.
He said: “I grew up reading the awe-inspiring sea-going odysseys of Shackleton, Heyerdahl and Knox-Johnston.
“In a world of ever-increasing risk avoidance and toxic screen time, let’s keep the spirit of adventure alive and inspire the younger generation.”
Louie, 52, is from Bolton and has served on special operations with the Irish Guards.
He suffered a severe brain injury in 2021, but still recently went on a skiing expedition to the Arctic Polar Circle.
Louie has worked for Royal Mail for the last 28 years.
They are making the journey to raise money for the charities Scotty’s Little Soldiers, which supports bereaved service children, and Alabaré, which rehouses homeless veterans.
The fundraiser has raised more than £72,000 so far.
The two men make up the entire crew of “Oceans ELITE”, but will be supported from shore by Mission Atlantic, an organisation that helps recovering veterans through the experience of open-ocean rowing.
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An Oceans ELITE spokesperson said: “Fewer people have rowed the Atlantic than have summited Mount Everest.
“The team will face hunger, exhaustion, monotony, dehydration, injuries, monster waves and harsh weather.
“Several crews have had sharks attacking their boat.”
Mission Atlantic is directed by Chris Martin who, along with former Royal Marine Mick Dawson, holds the world record for the first crew to row across the Pacific Ocean.
The crew will have to live off of dehydrated food and will have to desalinate their water.
You can support their fundraiser by visiting https://www.gofundme.com/f/oceanseliterow