ON THE SEA GYPSY IV, young pirates swill grog the cerulean shade of a swimming pool. The secret ingredient? "Blue soda," said Captain Ruby, "but I tell the kids it's fish blood."

Grog is one of many delights served up by Captain Ruby (Emily Tomasini) on "Pirate Adventures on the Chesapeake," a tour that flies the Jolly Roger. From April through October, the former teacher swashbuckles through Annapolis Harbor with an ever-changing crew of youthful mateys eager to seek sunken treasure, fight dastardly foes and even swab the deck. Proud owner of the Gypsy (and an experienced youth recreation coordinator), Tomasini runs a tight ship from which a rousing "Happy Birthday" frequently rises.

"We do a huge birthday-party business," said Tomasini, whose vessel sails six times a day, seven days a week. "Everyone wants to be a pirate."

That desire -- and two birthday parties -- were much in "yo-ho-ho" evidence last fall when my family embarked on the 75-minute cruise. The adventure began on a dock close to the Annapolis City Marina, where youngsters donned pirate vests and sashes, chose washable tattoos and painted curly mustaches on upper lips. After receiving special pirate names, the 20 boys and girls, ages 4 to 10, boarded the Gypsy. With a hearty "heave ho," we were off.

Tomasini, an avid boater with a captain's license, learned buccaneering skills by sailing with a similar operation in Cape Cod, Mass. She also researched a lot, she said, to flavor her tour with local lore. Tomasini's passion for pirates came through in her attention to detail. Even her T-shirt, front and back, bore the skull-and-crossbones of her trade. And she could toss out the lingo as lightly as did Johnny Depp in "Pirates of the Caribbean: The Curse of the Black Pearl," last year's hit movie. As her 35-foot-long motorboat chugged along the Severn River, Tomasini taught my daughter, "Castaway Christy," her friend "Hurricane Isabel" Wilder, both 5, and the other young derring-doers how to bellow "aargh" and literally put "all hands on deck." (Nets top the periphery of the boat to allow for safe observation while preventing "man overboard" problems.) The Gypsy's mermaid figurehead, 30-foot-tall mast, rope ladders and recorded sea chanteys set the scene for a thrilling trip. And the tour certainly delivered, with a narrative that actively engaged young buccaneers while entertaining onlooking parents (groups of kids must be accompanied by an adult).

Steered this weekend by a cheerful pirate named Crabby (Tomasini's husband, Michael), the Gypsy sailed straight for trouble: a lost treasure map! No sooner was it found and scrutinized by Ruby's enthusiastic crew then Pirate Pete loomed on the horizon. This scourge of the Severn (actually an actor in a small motorboat) also wanted the you-know-what. Luckily, the crew vanquished him with numerous squirts from the ship's 12 water cannons. Then an X-studded buoy floated by, cries rang out and soon all hands were tugging up a chest full of treasure. Crabby even supplied small loot bags so the young pirates could haul home their stash of pretend pieces of eight and plastic fish. Celebratory grog was passed around and the limbo danced. Ruby then calmed the excited little pirates with a lullaby, letting them "sleep off" their blue beverage as the Gypsy returned to port.

"What an adventure! It was one thing after another," exclaimed Kris McNally of Severna Park, whose twin boys, Seamus and Liam, 7, reveled in a birthday on board.

A peek at Tomasini's private life reveals that a pirate's work is never done. After her first busy season last summer, she spent the winter planning for this one. "I needed to hire staff, fine-tune [operations], double-check safety, buy loot," said Tomasini in a recent phone interview. "And in January, I was already booking school tours." Does she find herself talking pirate at home? "Oh, yes!" Tomasini said. "Michael and I are always calling one another 'Ruby' and 'Crabby.' "

Though eschewing the seven seas for the Severn River, Tomasini clearly enjoys her vessel. "This was my dream, to own a pirate ship," she said. "And I love sharing the fun with others."

PIRATE ADVENTURES ON THE CHESAPEAKE -- Boat sails from the end of Third Street, Eastport, Annapolis. From Washington, take Route 50 east to Exit 24, Rowe Boulevard, and follow Rowe as it curves to the right at Church Circle, then turn right at Duke of Gloucester Street and continue to end of street, turning right to cross Spa Creek Bridge. At first light after bridge, turn left onto Severn Avenue. Parking available at Annapolis City Marina for $1.75 per hour. Pirate Adventures dock is a short walk away and easily recognizable by adult pirates waiting to check you in. 443-398-6270. www.chesapeakepirates.com. From late April through October, pirate-themed boat tour in Annapolis Harbor and on Severn River. Seven days a week (weather permitting) at 9:30, 11, 12:30, 2, 3:30 and 5. Plan to arrive 30 minutes before sailing to allow time for pirate dress-up and face painting. $16 for ages 3 and older, $8 for under 3; $14 for ages 3 and older, $10 for under 3 for groups of 30 or more. $475 to rent entire boat. Reservations required by calling 443-398-6270 or e-mailing piratequest@hotmail.com. Ship capacity is 38 people, tours require a minimum of 16 passengers to run. At least one responsible adult must accompany a party of children. No public restrooms on board.

Little buccaneers blast Pirate Pete with water cannons during a treasure hunt in Annapolis Harbor.Maite Solis, Naomi Adedokun and Nicholas Nguyen, all 6, use a little elbow grease to hoist a Jolly Roger aboard the Sea Gypsy IV.