Susan Clark recalls the time she climbed aboard a ship outside Portland Harbor a few months ago.

The Croatian captain reacted with surprise to see that the man who would pilot his ship into the harbor was not a man at all.

“Only in America!” the captain said, raising his arms in disbelief. “Only in America!”

A Maine Maritime Academy graduate with plenty of experience at sea, Clark was the first woman to serve as harbor pilot. Now, she has broken another gender barrier as the first woman to join the Portland Marine Society, a group founded by ship captains in 1796 for “the promotion of the knowledge of navigation and seamanship.”

“This was a monumental event,” said Jeff Monroe, Portland’s waterfront director and a sea captain himself who is a member of the society.

Clark, who has been a licensed pilot since 2001, brings some of the biggest vessels into the harbor before tugboats take over. Some tankers stretch nearly 1,000 feet, weigh 160,000 tons and, with their bellies full of fuel, pass three feet from the ocean floor.

She is well aware of her responsibility, no matter how big the boat.

“You have to have a healthy respect for this,” Clark said, her expression serious on a recent day as she stepped off the deck of the pilot’s boat and grabbed the rope ladder to climb aboard the Elbrus, a 46,000-ton tanker carrying fuel to the ExxonMobil terminal.

With the support of her fellow harbor pilots, Clark joined the Portland Marine Society not to prove a point but because she loves her job and the centuries of tradition behind it.

“The pride in joining the society was how willingly they accepted me,” Clark said. “I know they didn’t let me in because I’m a woman. They let me in because I’m qualified.”

Clark, 40, was inducted at the May meeting at the society’s home in the Portland Harbor Museum at Spring Point, on the campus of Southern Maine Community College. The evening featured the usual vat of homemade haddock chowder, pilot crackers and bread-and-butter pickles.

Society members voted on Clark’s petition as they would have 209 years ago. They passed around a wooden box containing white and black balls. One black ball would have ended her bid.

The society’s early membership list includes such prominent Portland residents as Eliot Deering, John McLellan and Lemuel Moody. The group provided a much-needed forum where ship captains traded charts and tips on how to navigate foreign ports.

The society also helped to keep old seamen and their families from living in poverty in the days before better-paying salaries and pension.

Clark, who grew up in Norridgewock, decided to attend Maine Maritime Academy because she was good at math and science, and she thought it would provide travel opportunities.

Her travels as a ship’s officer took her around the world, including trips through the Panama and Suez canals, before she went to law school.

She practiced a few years at Verrill & Dana in Portland before realizing that sitting behind a desk wasn’t for her. She returned to Exxon, going to sea for two-month stints, and started training to be a harbor pilot in 1997.

Clark works 10-day stretches, guiding ships into Portland Harbor at the whim of the tides and the weather. Some days she’s at the helm at 3 a.m., then again at noon.

Whenever she can, Clark attends society meetings. She enjoys taking part in something that celebrates Portland’s seafaring heritage and its future.

She also looks forward to the day when she has enough standing in the group to make the chowder, using the society’s century-old recipe.

“That’s a privilege,” Clark says. “I don’t know if my hair is white enough for me to make the chowder.”