PORTLAND – Late last year, a committee of city and Portland Harbor officials sent a letter to then-Gov. John Baldacci recommending dredging along the eastern end of Portland’s “megaberth,” which was under construction.

But Ocean Gateway Pier II, which opened Sept. 10, was not dredged, and on Tuesday a cruise ship’s captain left the berth early to avoid shallow water.

The early departure exposed a limitation of the pier, which has been billed by the city as a deep-water berth. But city officials said it doesn’t indicate a design flaw in the berth, and noted that conditions like those on Tuesday are rare.

Maine Port Authority Executive Director John Henshaw, who was on the committee, said his group recommended that the water depth at the pier be at least 35 feet, the same depth as the shipping channel.

“To make it as usable as possible, having a … depth of 35 feet would have been desirable,” he said.

Portland Mayor Nicholas Mavodones agreed that dredging would improve the berth. “There is a need, down the road, to do additional dredging,” he said. “But there is no firm time line or budget put together.”

Mavodones said initial plans called for the berth to be above a 60-foot-deep hole where Bath Iron Works had a dry dock. The plan was altered during construction, and the berth was extended east, over the shallow water, to accommodate larger ships.

On Tuesday, the 951-foot Caribbean Princess shoved off the megaberth at about 2:30 p.m., even though it wasn’t leaving the harbor until 6 p.m., and rode out an astronomical low tide in deeper water. Some passengers who had left the ship were not notified and were later ferried from shore to the ship.

Mavodones, who manages operations for Casco Bay Lines, said, “It won’t (happen) frequently.”

Mark Klopp, a harbor pilot who guides large ships into and out of the harbor, said the 2:30 p.m. pier departure of the Caribbean Princess was planned well in advance. He said most big ships plan their schedules around tides.

“It was not a problem for that ship, being at that berth,” he said, noting that ships are required to have at least one foot of water under their keel at a pier. “There are other ports where they have to watch the tides. We are not alone. Portland isn’t like a sore thumb.”

Portland’s spokeswoman, Nicole Clegg, said the water on the east end of the berth — the shallowest part — is 30.1 feet deep at the average low-water mark. But Klopp said ships use a different figure, called the “controlling depth,” which is 29.1 feet at the same point.

Because of gravity from the moon and planets, the water fell 1.37 feet below average at 5:24 p.m. Tuesday, according to the National Oceanic and Atmospheric Administration. Therefore, the depth at the pier could theoretically have been 27.73 feet.

The Caribbean Princess draws 27 feet, meaning the bottom of the ship might have had just 8.8 inches of clearance at low tide. Other cruise ships visiting Portland this fall draw 26 to 29 feet.

According to NOAA predictions, water levels in Portland Harbor are expected to drop 1 foot or more below the average low-water mark on 57 days in 2011.

The water level will drop below average again Sunday, when the Jewel of the Seas, which draws 28 feet, is scheduled to be at the megaberth from 7 a.m. to 6 p.m. The tide will not be at its lowest until 10 p.m.

Seven other ships are scheduled to use the berth before the season ends Oct. 23, but none of those visits will coincide with the lowest tides.

Other factors, like offshore winds, can make sea level fall several inches more than predicted, said Robert Eldridge White Jr., publisher of the Eldridge Tide and Pilot Book.

A ship’s position at the pier is another factor. A ship with a deep stern, tied with the stern to the east, could have less clearance, said Clegg.

Klopp said captains decide how to dock based on the location of their passenger doors.

Accounts of the circumstances of Tuesday’s early pier departure by the Caribbean Princess differ.

Klopp said the ship was scheduled “months in advance” to leave the berth at 2:30 p.m.

“This is common,” he said. “We plan around (the tides).”

And Mavodones, who met the ship’s captain earlier Tuesday, thought the crew had told passengers of the change before they disembarked.

But a Princess Cruises spokeswoman called the early pier departure unplanned.

“We weren’t able to communicate this change to those passengers who were ashore at the time,” said Karen Candy, manager of media relations. “We reacted to the tidal conditions at the time.”

Candy noted that the cruise line transferred passengers safely from Portland to the ship, which was then in the harbor, using tenders. The ship left Portland Harbor at its scheduled time.

“This unusual weather condition will in no way impact our decision to continue to bring passengers to Portland,” she said.

Staff Writer Jonathan Hemmerdinger can be reached at 791-6316 or at:

[email protected]