Brelet said the submarine capsule showed "dangerous levels of carbon monoxide" but tests later showed the fuel cell was, in fact, leaking hydrogen.
Citing safety reasons, Delafargue and Lagarde decided to call off the mission and try again next year, Brelet added.
On the project's website, it explains that, as well as crossing the stretch of sea, the two men aimed to film the ocean bed and promote energy conservation.
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"We want to wake people up from their power and gas guzzling dreams," they said in a statement.
Delafargue told British media he had funded the project himself at a cost of some £100,000 (118,000 euros, US $130,000).
"I'd always wanted to build a submarine since I was a kid," he said.
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