Doug McConnell has a grasp on all the factors he can control. So when he set off this morning on his third attempt to swim from Nantucket to the Vineyard, a distance of about 18 miles, all that lay in front of him was a battle against what he can’t control: the fast-moving currents of Nantucket Sound.

“We’ve learned a ton in the first two,” Mr. McConnell, 64, told the Gazette in an interview the afternoon before the big swim.

But it still wasn’t enough. Mr. McConnell entered the water off Nantucket at 8:45 a.m. but at 1:50 p.m. he was pulled up onto a boat by his guides. He was still nine miles away from the Vineyard.

Victory even in defeat: the swim raised $30,000 for ALS. — Susan McConnell

“It’s with heavy hearts we are breaking the news that our swimmer called it,” his wife Susan McConnell posted on Facebook from the boat. “The beginning of the swim had a strong current that complicated the outcome and the window closed. Nothing worthwhile is easy. Everything worthwhile is hard. The ocean won this time.”

Mr. McConnell has completed many other long-distance swims — across the English Channel, the Catalina Channel, the Molokai Channel, a swim around Manhattan, to name a few. But the Nantucket to Vineyard swim continues to elude him for the third summer in a row. Deb Taylor Blair and James Pittar have successfully gone the other way but no one has yet completed the Nantucket to Vineyard leg.

Mr. McConnell began doing long-distance swims about 15 years ago as a way to build awareness and raise money for amyotrophic lateral sclerosis, known as ALS. His foundation is called A Long Swim and the cause is a deeply personal one. Mr. McConnell lost both his father and sister to the disease.

“The ability to marry up a niche sport like long-distance swimming with a niche disease like ALS seemed like a perfect fit,” he said.

Mr. McConnell said he has seen breakthroughs in ALS research become more and more frequent since he began his efforts. He estimated approximately 5,000 people will be paying attention to his swim today.

“It’s a wonderful, gratifying thing to see that many people follow us,” he said.

Doug McConnell and his team after the swim. — Aidan Pollard

The swim raised $30,000 for ALS.

After the swim, Mr. McConnell said he was disappointed, but he said he knows its a distance he can conquer.

“It is a completely doable swim,” he said.

He said the first three miles of the swim were the toughest, and at one point cramps were bad enough that he was having a hard time finding a consistent rhythm.

“I was having trouble putting 100 strokes together,” he said.

Still, Mr. McConnell said he made it about 10 miles, totaling around 11,000 strokes. And he said it won’t be long until he starts thinking about the next one.

“It will be by the time I get back to the house,” he said.

For more information about Doug McConnell and his foundation, visit alongswim.org.