THE “SEVEN MILE MIRACLE,” a stretch of coastline on Oahu’s North Shore, is the holy grail of big wave surf spots. It is also one of the most dangerous surf breaks on Earth. The lifeguards who patrol the beaches make upward of 1,000 saves per year, sometimes as many as 30 in one day. Tau Hannemann, a 15-year lifeguard veteran, is known as one of the best on Oahu. For Hannemann, lifeguarding is more than a job, it’s a calling.