Lecomte will swim for eight hours a day before resting on the 20-metre support boat that will accompany him throughout the journey.
The team, working with 12 scientific institutions, including NASA and Woods Hole Oceanographic Institution, will conduct oceanic and medical research throughout the journey.
After successfully completing the Atlantic swim, Lecomte vowed "never again" to set off on a long-distance sea journey.
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I'm not ever going to try to be a person that isn't nice, so that feels more authentic to me and, you know, I think I'm still doing okay.
When Ben Lecomte stepped on to land for the first time after swimming across the Atlantic Ocean in 1998, he told himself "never again". "Rather than calling it an island of trash, it is more like plastic smog throughout the ocean".
"The mental part is much more important than the physical".
"I remember my father and he was the one who taught me how to swim in the Atlantic".
"When I was little and I was with my father walking on the beach, I didn't see any plastic, or hardly any. It's a problem we created and there is a very easy solution to start reversing it-single-use plastics for example, if we stop using them that will make a big change". However, his achievement was not documented, therefore it is not recorded in the Guinness Book of records.
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"It is mind over matter", said Lecomte, who is also an architectural consultant based in Austin, Texas when not in the water.
A crowd of around a few dozen people gathered at the beach in Choshi, a couple of hours from Tokyo, to see the swimmer off. Lecomte, wearing a wetsuit and flippers, drew cheers as he set off doing a brisk crawl.
"The worst thing that can happen is not knowing what you are going to do with your mind and going to the wrong place", he said. Ahead lie several months of unpredictable and at times turbulent weather, extremely cold water, not to mention the danger posed by sharks and jellyfish.
However, Lecomte could not wait to get started.
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'It made me think what (the) future for my kids is going to be like.