"If you don't make the wave, the jet ski will come get you. In 2000 we started using life jackets, so as long as you can hold your breath under water for long enough, you're OK."
It's perhaps that practical attitude which has seen McNamara smash surfing records.
In 2011 he rode the biggest wave in the world -- a 24-meter monster in Nazare, Portugal. Earlier this year he returned to the same spot to ride another huge wave, that may have been up to 30 meters high.
"I'm looking for the rush," McNamara said. "But lately I've had a really hard time finding it.
"When I surfed the glacial wave it was mind-bending, it was the heaviest rush. But since that day I've found it difficult to get that rush in the ocean. It made me realize how comfortable I feel on big waves."
McNamara's describes his obsession with that elusive rush as "like a monkey on my back." Though he chuckles as he adds: "I think the monkey's starting to lose his grip."