LOS ANGELES — Zac Sunderland is alone on a sailboat off Indonesia, five months into a journey around the world, when he senses the worst kind of danger.

Pirates!

A large wooden vessel in the distance, rising and falling over the swells, is clearly on intercept course. It does not show on the radar. It flies no flags. Its crew doesn't respond to radio calls. Sunderland alters course, the pursuers do likewise.

What's a 16-year-old to do? Sunderland isn't sure, so, with his heart racing, he dials home on the satellite phone.

Laurence Sunderland, a longtime shipwright and yachtsman, has just begun Sunday dinner with his wife and six other children in their Thousand Oaks home north of Los Angeles when the phone rings.

A daughter answers and Zac's shout erupts through the receiver. Laurence snatches the handset and rushes into another room.

He calmly instructs Zac to load his .357-caliber pistol before announcing his plight and position on the emergency radio channel.

The father then directs his son to be prepared to shoot to kill.

"It's hard to tell a 16-year-old that, but this is real life, not a video game," Laurence recalls. "I said if they have guns and they're coming to do you harm, you're going to have to shoot to kill. Otherwise, you will be killed."

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Zac Sunderland had long since discovered that trying to become the youngest person to sail around the world alone is not child's play. He has until January 2010 to break a record held by David Dicks, an Australian who was 18 years, 41 days old, when he accomplished the feat.

Sunderland, though he could not legally drive a car, piloted the 36-foot yacht Intrepid 5,000 miles across the Pacific Ocean during the initial leg to the Marshall Islands. He endured long windless periods as well as violent squalls and turbulent seas.

His parents were criticized for allowing their oldest son to trade a normal teenager's life for such a dangerous existence, despite his extensive sailing background.

Their son, who says he's chasing a dream, now has 12,000 miles under his keel. He's due any day at Mauritius, off Africa, which will mark his halfway point.

But he'll have little time to celebrate. His beleaguered boat requires extensive repairs and the most treacherous portion of his journey -- from Mauritius to Durban, South Africa, and around the Cape of Good Hope -- lies directly ahead.

"It's been frustrating," he said on Election Day, as a disabled front sail flapped in the background. "Because whenever anything goes wrong, it always happens in the middle of the night."

How long ago it must seem that the 6-foot, 165-pound teenager, a high school sophomore, embarked from Marina del Rey, a small harbor south of Los Angeles, on June 14, 2008, looking both heroic and naive.

Since then, he has lost weight and become hardened beyond his years. It was just four weeks ago that presumed pirates in the 60-foot wooden boat sized him up as he sailed south of Indonesia, a reputed trouble spot.

When the boat closed to within one-quarter mile, Sunderland said, "I jammed some bullets into my gun and just waited."

The vessel, its crew hidden, swept to within 200 yards, into Intrepid's wake, and remained several minutes before changing course and motoring off.

"I'm not sure how useful it would have been if it was a boat full of pirates," Sunderland said, referring to a weapon he surrenders to authorities at every port. "But I didn't get to find out, so it's a good thing, I guess."

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The journey has exacted no small toll on his parents and siblings. Costs for the largely unsponsored project have been so overwhelming the family has set up a donation link on the Zacsunderland.com Web site.

Zac phones home twice a day, in mornings and evenings in Southern California, so rings at other times cause anguish.

His parents, who remain fiercely supportive of Zac's ambition, will not forget the day -- as Zac was negotiating the hazardous Torres Strait between Australia and Papua New Guinea -- he dropped his satellite phone into sink water.

It sent an erroneous signal to the phone company, relayed to the parents, which placed Intrepid's position atop a reef 120 miles off course.

They were moments from initiating a search-and-rescue mission when a message, delivered via high-frequency radio to their computer, stated, "Hi mom. I'm OK."

"He was oblivious to our concerns and just happened to send that message," Laurence Sunderland said.

More recently, as Zac traveled from Darwin, Australia, toward Cocos Keeling Islands, Intrepid was tossed about so violently during the night that its tiller arm broke.

Zac pieced it together with clamps, but steering was difficult even with autopilot, and when the boat jibed abruptly the boom swung swiftly over deck and snapped, leaving Intrepid without a working mainsail.

Intrepid limped into Cocos Keeling, where Sunderland -- using his parents' credit card -- sought a carpenter to make a new tiller and fashion a sleeve around the broken boom.

His troubles worsened in recent days, as violent winds tore loose part of his front sail rigging. He worked through the night on deck in 12-foot seas, strapped into a harness, water cascading around, trying to furl the sail and gather its rigging.

"I've been telling my friends to pray for him because the next four days could be a long four days," Marianne Sunderland said Monday, as her son pushed toward Mauritius.

"It's hard because I know how tired he is. He's not eating right. He can't cook or even clean up when it's rough."

Persistent problems prompted a diversion to a nearby island, further delaying Zac's arrival at Mauritius, where his father awaits with tools and a new boom.

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Remarkably, when Zac was reached Tuesday evening -- Wednesday morning in the Indian Ocean -- he sounded as calm is if he were home on the sofa.

He confessed to eating cold meals from a can, to not having energy to wash after so much work, and to missing his family.

But he has visited so many places, made so many friends. He'll spend Thanksgiving and his 17th birthday, Nov. 29, hurrying to Durban, trying to beat the storm season.

What he may not know is that he'll take from Mauritius dozens of birthday presents and "a microwave cake complete with candles," his mother promised.

With luck, he'll enjoy enough leisurely moments to savor them.