"I don't think about it too much because you just can't," he said. "And I have all the survival gear."
In addition to the typical life vest and dingy, Zac's 36-foot Islander sailboat -- which he bought with $6,500 he'd saved during his childhood -- is equipped with state of the art technology, including a satellite phone, radars and GPS systems.
Still, even with all the gear, many experienced sailors are daunted by the prospect of such a trip.
Six-time world sailing champion Derrick Fries told ABCNEWS.com that even he wouldn't attempt it.
"There will be times when it's absolutely ecstasy, and it will be sunny and the ocean will be calm," said Fries. "That will be great but it may only be 7 percent of the time."
"It's a highly risky endeavor, I wouldn't do it," said Fries, who said the chance of Zac not experiencing mechanical failures is extremely unlikely.
Before even setting sail, Zac ran into some difficulty and had to postpone his departure by two weeks. The engine failed and needed replacing, he said.
While many parents would never let their child sail off into the sunset alone, some parenting experts told ABCNEWS.com that taking risks is part of growing up.
"When calculating a risk, it's important to take into account who you are and what you know," said parenting expert and founder of Teenfrontier.com Barbara McRae. "He's been a sailor since childhood and was essentially born on a boat."
"I'd say Zac is ready to live his dream," said McRae, who added that the same answer would not apply to all risk-taking kids, and depends entirely on the individual child's experience.
"If it were a situation where somebody was not prepared and was not passionate I'd say absolutely not," she said. "I don't think the [Sunderland parents] are being bad parents -- they're supporting their son with his dreams and not allowing their fear to get in the way of that."
The Sunderlands are not the first parents to let their children take such journey. At age 18, Australian Jesse Martin, a good friend of Sunderland's, made a solo-trip around the world.
In 1965, American sailor Robin Lee Graham became the youngest to boat across the world when he sailed into his final port at 20 years old.
Zac said it was Graham's successful adventure -- and a book of photographs published about it -- that inspired him to try it himself. He plans to keep his blog updated and film a documentary during his trip. He is also bringing his school books along and plans to study on the way.
And for Marianne Sunderland, letting herself or her son live a life controlled by fear is simply not an option, no matter what her critics may argue.
"There are risks, but we look straight at them and minimize them and feel that it's not negligent by any means," said Sunderland. "I obviously don't want him to die, but I would not have any second doubt."
"If [he died] it would be devastating, but you can't live life ruled by fear," she said.