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Waves, wind and darkness hampered the ocean search off Hawaii for a Chinese man reported missing while attempting to set a sailing record, the U.S. Coast Guard pilot who was the mission's air commander said Thursday.

"It was pretty frustrating not to find him, not to hear him," Lt. Ben Powers said at Air Station Barbers Point in west Oahu, the morning after the Coast Guard called off its search for Guo Chuan. "The hardest thing we do is search for a person in the water because it's a huge ocean."

Guo, 50, was attempting to set a sailing record from San Francisco to Shanghai. The search was suspended after a U.S. Navy crew from the USS Makin Island went aboard Guo's 97-foot trimaran about 620 miles northwest of Oahu and found only his life jacket.

As one of the pilots of one of the HC-130 Hercules planes that participated in the search, Powers spent hours scanning the ocean for Guo through 4-to-6-foot waves. There was no moon, he said, so illumination was low even with night-vision goggles.

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Rescuers radioed Guo every 15 to 30 minutes, Powers said. There was no response.

"When the person's in the water basically the only thing above the water is the person's head," Powers said. "So that's really what we're looking for — something the size of a human head from an aircraft from 300 to 700 feet."

Because Guo's boat was well-tracked, rescuers had a good idea where he fell into the water, Powers said.

Guo "was a professional mariner with a deep passion for sailing. Our thanks to our Navy partners who helped us search for this vessel in a timely manner so far from shore in an attempt to locate Mr. (Guo) Chuan. Our deepest condolences go out not only to his family and friends but also to his racing team and the sailing community," said Capt. Robert Hendrickson, who directed the Coast Guard's search.

Guo's sailboat, the Qingdao China, is adrift, and its main sail has been taken down, the Coast Guard said. The Coast Guard says it broadcast a warning to mariners to beware of the drifting boat.

Guo's racing team plans to recover the sailboat, the Coast Guard said.

Guo was the first Chinese person to sail around the world in 2013, according to his website, guochuanracing.com.

Guo left San Francisco on Oct. 18 to challenge the solo nonstop trans-Pacific world record. The current speed record for that journey is 21 days, and he was trying to sail from San Francisco to Shanghai within 20 days, the website says.

In Beijing, the Foreign Ministry said on Thursday that China's consulate general in Los Angeles had alerted the U.S. Coast Guard in Hawaii when it learned that Guo could not be reached. Spokesman Lu Kang said Chinese diplomats had helped in the coordination of the search and continued to monitor the situation.