Sea birds were the guides that brought the voyaging canoes Hokule'a and Alingano Maisu with pinpoint accuracy to tiny Johnston Atoll, said Hokule'a navigator Bruce Blankenfeld.

But Polynesian Voyaging Society president Nainoa Thompson credited Blankenfeld himself for accomplishing an exceedingly difficult task in nearing a single small atoll after sailing through winds that required long tacks — some of them taking the canoe away from its goal — and then using available clues to bring the canoes within sight of land.

"He did the perfect sail," Thompson said.

The canoes, accompanied by escort boat Kama Hele, are using traditional Pacific Islander non-instrument navigation on a voyage from Hawai'i to Micronesia. Upon arrival they will deliver the 54-foot double-hulled canoe Alingano Maisu as a gift to master navigator Mau Piailug, who taught Hawaiians the lost art of wayfinding — non-instrument navigation.

Thompson said that "Papa Mau" taught the very techniques that are bringing this small fleet of boats to his island, Satawal. Blankenfeld aboard Hokule'a was lead navigator from the Big Island to Johnston, and Chadd Paishon aboard Maisu has now taken over as lead navigator for the fleet — heading for Majuro Atoll in the Marshall Islands. The canoes are well past halfway this weekend.

Their first big success on the larger voyage was actually sighting Johnston, a flat, small island that is hard to spot. Very hard to find and very easy to miss, Thompson said.

He described two different parts of the non-instrument navigational world: first, using available clues like stars, clouds and waves to steer the most accurate route between two points. But inevitably, there is some error.

"Dead reckoning is not as accurate as a sextant and GPS (satellite-based electronic navigational instrument)," he said.

The goal of that part of the navigation is to get the canoe into what Thompson calls "the ring," the circle formed by the maximum range of sea birds that nest on land and fly daily far out to sea. Birds provide a natural error-correction system. If a sailor sees the white tern or manu o Ku, he or she knows land is within roughly 120 miles.

Blankenfeld, interviewed by satellite phone, said he had had cloudy weather, which prevented him from seeing stars and judging his latitude — it turned out he was on a line that would have passed north of Johnston. But then he entered the ring of the birds. They saw two manu o Ku on one day, and two on the next. But they missed the telltale sign of seeing birds at sunset lift off the water and head directly home.

"The birds rise and they fly like an arrow to the island — but sometimes they may not give you the gift off flying straight," Thompson said.

Another clue can often be found at dawn, as birds fly from their island to distant fishing areas.

"On the second morning before we saw the island, you could see the 'iwa and other birds coming out of that one area," Blankenfeld said. He turned his canoe to port, and two days later crew member Kaleo Wong spotted the only building, a concrete structure, on unpopulated Johnston.

Thompson said there are multiple tips a voyager can tap into when in the island-finding mode.

Blankenfeld said he looked for other clues, but didn't find them.

One he sought was the telltale green tinge on the bottoms of low clouds over a lagoon, which is the reflection of the sunlight from the shallow sand bottom. Johnston didn't have it, Blankenfeld said.

Sheer numbers of birds are another clue.

"The closer you get, the more birds you see. If on the second day after entering the ring (of birds around an island) you see a lot of birds, you know it's near," Thompson said.

Some islands will reflect waves, and a skilled navigator can detect them. But Thompson said most atolls don't provide much reflection of waves, and Blankenfeld said he didn't notice any.

Occasionally, when approaching an island, a particular swell coming from ahead disappears.

"Sometimes the waves are breaking over the windward bow and they make the deck wet. Then you notice the deck is dry, because the atoll has cut off that wave. That's a really good sign that the atoll is upwave from you," Thompson said.

Different fish may come up on trolling lines as land nears.

"You catch different fish, like barracuda, which we never catch in the deep sea. And kahala," Thompson said.

The navigator's focus changes as land nears, he said.

"You start to look at nature — the ocean — in a different way once you're in 'the ring,' " he said.

Now that the canoes have passed Johnston and are aiming for Majuro, which is still about 1,000 miles away, navigator Paishon is trying to sail as accurate a route as possible to get himself into the ring around Majuro or one of its nearby atolls.

"We are sailing manu kona (southwest on Thompson's star compass)," Paishon said by satellite phone Thursday afternoon. "Right now we're using the sun and the swells. At night we use the North Star, hoku pa'a, and we have several different ones that we use. And there's Jupiter in the morning."

Steering, he said, is relatively easy at night when stars are present as guideposts. The most difficult time is the middle of the day, when the sun is overhead and not useful as a steering aid.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.