All 62 passengers aboard the Discovery were evacuated without incident, the Coast Guard said, with the Lahaina Princess giving the stranded vessel a pull off the reef.

"They zigged when they should have zagged," Capt. David Jung said of the Lahaina Princess.

Jung and other witnesses said the Discovery was headed out from Lahaina at about 8 a.m. when it swung wide onto a sandbar on the north side of the entrance channel.

"The conditions were fine," Jung said. "We're having some silting on the north side of the channel, and the PWF catamaran made a sweeping, wide turn and got hung up on the sandbar.

"The tide was low, but that's not the problem. You have to keep your boat in the channel."

"It's not usual for people to go aground," said Lt. Darwin Jensen, a Coast Guard marine safety officer on Maui who said there will be an investigation of the incident.

Anne Rillero, a Pacific Whale Foundation spokeswoman, said the Ocean Discovery was inspected after it was pulled off the reef, taken through a sea trial by the Coast Guard and certified to return to service.

"Due to an extremely low tide, Pacific Whale Foundation's Ocean Discovery became temporarily lodged on sand just inside the breakwater of Lahaina Harbor at 8:05 a.m.," she said.

The passengers were helped ashore by the Dolphin, operated by the West Maui Parasail company.

"There were no injuries. The Coast Guard and Lahaina Princess assisted in dislodging Ocean Discovery from the sand," Rillero said.

A harbor worker, Mona Cherry, said the grounded catamaran blocked a number of vessels approaching the harbor, including the Expeditions ferry from Lana'i.

"Everybody's schedule was totally messed up. There were cancellations and delays affecting a lot of people," she said.

Kahului businesswoman Carolann Guy said she was at the harbor at about 10 a.m. to pick up a friend, and she saw a helicopter overhead and several boats and dinghies trying to assist the Ocean Discovery.

She counted two Lana'i ferries, a Trilogy excursion boat and one or two others waiting outside the harbor. Shortly before 10:30, Guy said, the Lahaina Princess pulled the Discovery off the sandbar.

The ocean level was unusually low, according to Zoe Norcross-Nu'u, Sea Grant Coastal Program extension agent. She said several people had commented on the low water, which was probably a coincidence of two features — a spring tide and a large eddy or bulge in the sea surface that was moving past the island at the same time.

"It isn't rare, but it doesn't happen every month," she said. This week's low "might have been even lower than they predicted," she said.

An NOAA forecast for tides off Lahaina for May indicated that an extreme minus-0.6 foot low tide was occurring since Tuesday. The minus-tide was forecast for 9:48 a.m. Friday, resulting from the moon being aligned with the sun. The new moon over Hawai'i was on Wednesday, while on Friday in Lahaina, moonrise was at 7:29 a.m. with sunrise at 5:48 a.m.

Spring tides occur at new and full moon and create the highest high tides and the lowest low tides, said Norcross-Nu'u. Extreme tides could have combined with a passing local mesoscale eddy to generate lower-than-normal sea surface levels, she said.

"It's been amazing," Cherry said at Lahaina Harbor. "Yesterday, they saw coral sticking out of the water that they've never seen before."

"The tide was very low this week and the master departing the harbor may have run into a high sandbar," Jensen said.

"Anytime somebody goes aground, the Coast Guard will conduct an investigation into the reason for the grounding and work with the company and master to prevent it from happening again," he said.

Initial reports from the Coast Guard were that the grounding generated no pollution. Crew from the Coast Guard Ma'alaea station and the cutter Ahi responded to the incident, along with a rescue helicopter from Air Station Barbers Point, but Lahaina boaters credited Jensen with coordinating the response.

"I just made sure things kept moving in the right direction. The Lahaina Princess and Dave Jung were instrumental in helping to get the vessel off," Jensen said.

"The Dolphin and the captain of the Dolphin helped to bring all of the passengers off safely with the assistance of the crew of the cutter Ahi. It was a very orderly evacuation."

"It was a tricky spot. We had to pull from the bow, and that made it a little dicy," Jung said. He said he was happy to be able to reopen the harbor.

"They shut down the harbor. The Lana'i ferry couldn't come in," he said.