Before Benoit Lecomte waded into the surf off north-east Japan on Tuesday to begin his 5,500-mile swim across the Pacific Ocean to San Francisco, his biggest concern was not the distance, storms, exhaustion or even sharks. The biggest test, he said, will be the monotony.

"The challenge is to keep doing the same thing for hour after hour and day after day", 50-year-old Mr Lecomte told The Telegraph before his departure from Choshi Beach, to the north-east of Tokyo. "I need to be physically prepared, of course, but more than that I need to be mentally ready".

To keep the boredom at bay, and to perhaps stave off thoughts of just how far he still has to go before he passes beneath the Golden Gate Bridge, Mr Lecomte draws up a detailed schedule of what he will think about for each of the eight to 10 hours he will spend in the water during the epic swim.

"I break it down into sections during which I relive past events with my family, or I try to picture a city that I have never visited, walk through its streets and visualise people," he said in. "I try to get into as much detail as possible - to sense the wind or the scent of a person walking by.