McNamara's record-setting feat was verified by Guinness after an independent panel of big wave and photography experts painstakingly measured still and video images of the colossal wave, a spokeswoman for the agency said. (Video: http://r.reuters.com/fuq28s )
"I was totally in the moment. PCP. Present, connected and protected," McNamara, 44, told Reuters in a phone interview from his home in Haleiwa, Hawaii, on the North Shore of Oahu.
According to Guinness, the epic feat eclipsed by more than 1 foot the previous record, set in 2008 by big-wave surfing great Mike Parsons at Cortes Bank in California.
McNamara, who has surfed professionally since age 17, said he had not planned on going to the beach at all on the day he set the record after spending the entire previous day in waves that "believe it or not were a little bigger."
He said friends woke him up early and persuaded him to come with them and that he went reluctantly -- feeling "beat up" from the day before and only planning to drive the jet-ski used to tow big-wave surfers out far enough to catch the break.
"They talked me into getting on my board," McNamara said. And when I got on the board and they pulled me up with tow rope everything just felt right, it was like magic."
Towed out into a set of enormous waves by the jet-ski, McNamara passed up the first swell when he saw the record-setting behemoth shaping up ominously behind it.
"We saw it coming from way out and my lady Nicole (Macias) was on the radio saying 'there's a big macker coming on the outside!' and telling us where to go," he said. "The guy tried to drive me into the first wave and I'm all 'No, No. 2, No. 2! There was just this monster."
McNamara said he was caught up in the moment as he rode the wave, then worked to stay in control of his board as the colossal wall of water drove him straight toward rocks where "if you fall, there's not much chance of survival."
The surfer said he knew the wave was big but was not sure he had set a record until it was made official last week at the Billabong XXL Global Big Wave Awards in Anaheim, California.
"I really just surf for the love of it and I wasn't looking to get the record. I wasn't looking to get any awards," he said.
"One the main reasons I'm doing this is to hopefully inspire at least one person to do what they love, to do what they are passionate about," McNamara said. "I am living proof you can do what you love as a career."
(Reporting by Dan Whitcomb; Editing by Cynthia Johnston and Lisa Shumaker)