His yellow swim cap and blue goggles appeared, then disappeared, in the water off Cedar Town Beach, about 50 feet from shore. He moved as if gliding atop the waves, crisp arm strokes coupled with quick kicks of his legs.

Every movement was precise. No energy wasted.

For Bill Van Nostrand, 54, of East Setauket, it's the calculated choreography of triathlon training after his work managing a laboratory at Stony Brook University's Department of Neurosurgery. His goal: to swim, bike and run a total of 140.6 miles in 17 hours in New York City's first Ironman event next month. In doing so he will help call attention to Alzheimer's disease.

"I like this beach," he said later, unzipping his black wet suit at a picnic table in Mount Sinai. "Usually it's nice and protected from the wind."

Wind is just one of the elements Van Nostrand may face on Aug. 11, when he competes in the 2012 Aquadraat Sports Ironman U.S. Championships.

The competition will be Van Nostrand's eighth Ironman since 2007. He has about 20 half-Ironmans under his belt.

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"Everyone thinks it's all physical. It's actually 90 percent mental," said Van Nostrand, who is 6-foot-2 and weighs about 185 pounds. "You can't just go out and just go as fast as you can. You've got to pace yourself for the duration of the day."

Pacing is essential, too, in Van Nostrand's work as a neuroscientist who has researched Alzheimer's disease for about 25 years. In the upcoming triathlon, he'll be one of 18 people on the Athletes for Alzheimer's team, each of whom has pledged to raise a minimum of $5,000 for the Alzheimer's Association, New York City Chapter, director of operations Nicholas Emerson said.

"He's a laid-back, friendly guy," Emerson said about Van Nostrand. "But he's very serious and passionate about raising awareness about Alzheimer's and trying to find a cure."

That passion deepened three years ago after his father, Robert Van Nostrand, 73, of Farmingdale, died of Alzheimer's disease.

"The most difficult thing about it was the frustration with my mother . . . She always asked me, 'Isn't there something we can do?' " Van Nostrand said. "It's hard to tell someone in your family that really there's not much you can do."

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His father went from forgetting to buy items at the grocery store to having tremors and needing help getting to the bathroom and with eating, he said.

"Seeing his father degenerate like that . . . I think that made him more determined for his research and doing these Ironmen," said Van Nostrand's wife, Judianne Davis-Van Nostrand, 50, who works as a research associate in his lab.

In her opinion, her husband "intensified his concentration on his training" following his father's death.

John Robinson, a biological psychologist at Stony Brook's Department of Psychology, trained with Van Nostrand during bike rides on Route 25A.

"We do an 80- to 90-mile ride," said Robinson, 48, of Poquott. "I usually quit at mile 30."

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But Van Nostrand keeps going, alone. "Anybody who can complete a full Ironman . . . has to be extremely dedicated and well-organized," Robinson said. "He's not somebody who wastes time."

Time also is critical in a climate in which government funding for research is steadily declining, Van Nostrand said.

"With Alzheimer's disease, it's being penny-wise and pound-foolish," he said, adding that the number of Alzheimer's patients will increase in 10 to 30 years as baby boomers age.

"If we don't do something now and be proactive about it, we're going to be really paying the price down the road," he said.

Betty Bosler, an administrator in Stony Brook's Department of Neurosurgery, said Van Nostrand's work focuses on aspects of the amyloid beta protein that accumulates in the brains of Alzheimer's patients.

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"Somebody who works every day on these minute little genes and proteins, it's not so sexy as [a physician] saving a life and it's very, very hard work," she said.

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Tax-exempt donations to the Alzheimer’s Association’s New York City Chapter on behalf of Stony Brook neuroscientist Bill Van Nostrand can be made to alznyc.org/ironman, or call 646-744-2900.

Tax-exempt donations also can be made through the Stony Brook Foundation’s Cerebrovascular Disease Research Account at stonybrook.edu/sb/giving, or call 631-632-6536.