Rennes - Two French engineers have been forced to end a bid to cross the Channel in a pedal-powered submarine after encountering technical problems, their team said on Monday.Antoine Delafargue, 34, and Michael de Lagarde, 35, set out from Plymouth in southwest England on Friday in a 3-ton, 6m-long submarine.The two men had hoped to complete the 250km crossing to Saint-Malo in northwest France within a week, each pedalling for up to 12 hours a day - the equivalent of a stage of the Tour de France every day.But within hours of being submerged they were forced to return to port after a vessel tracking the submarine lost the use of its sonar, Gael Brelet, a spokesperson for the Pilot Fish Project, told AFP. On their return to Plymouth the sailors also noticed another problem. 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."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 about $130 000."I'd always wanted to build a submarine since I was a kid," he said.