Three mammoth waves appeared and Cotton towed McNamara onto the shoulder of one.
"Everything seemed to be perfect, the weather, the waves," said Mennie, who acted as lifeguard for the event
"I had the best seat in the house as he dropped down the face of the biggest wave I've ever seen. It was incredible.
"Most people would look scared but Garrett looked in control as he went down the most critical part of the wave"
The previous world record was set in 2008 by Mike Parsons, who rode a 77-foot wave at Cortes Bank, a shallow reef that sits 100 miles off the coast of southern California.