The U.S. Coast Guard on Wednesday continued searching a large area off the coast of Long Island for a Middletown woman and her son who left Point Judith, R.I., in a 32-foot aluminum boat Saturday night and haven't been heard from since.

The search began Sunday night and by Tuesday had expanded to an 11,000-square-mile area of the ocean, "roughly twice the size of Connecticut," the Coast Guard said.

"We are still actively searching for the mom and son," Petty Officer 3rd Class Nicole Groll said Wednesday.

Search vessels from Cape Cod, Maine, New York and North Carolina were involved.

The Coast Guard said the Carmans left Ram's Point Marina at Point Judith late Saturday.

Linda Carman, 54, and her son, Nathan Carman, 22, let friends know Saturday night that they were heading to an area southeast of Block Island to go fishing and were to return Sunday morning.

"They file a float plan with me when they go," said Sharon Hartstein, Linda Carman's close friend. "It would be unlike her to change plans without telling somebody. We're very anxious and very worried."

A float plan gives details of a boating trip, including destinations and passengers, and is usually left with a marina or a friend in the event the vessel doesn't return on time and authorities need to be notified.

Hartstein said Nathan Carman moved to Vermont in recent years and meets up with his mother regularly to go fishing off the coast.

"Linda and Nathan go out at least monthly," she said. "They like to fish. Linda doesn't eat fish so she either throws it back or she cooks it for Nathan."

Hartstein said the two usually leave the marina late at night or early in the morning — sometimes 2 or 3 a.m. — to do their fishing.

Hartstein said Linda Carman sent her a message Friday to say she wouldn't leave that night as planned but would leave Saturday night instead. Hartstein and another friend received the same text message before 11 p.m. Saturday that said they were pulling away from the marina, but neither has heard anything since then.

"We're all very concerned. She does a lot of good in the community, and if anybody needs anything she's there to help," Hartstein said. "I know she would never decide to extend the trip without letting someone know, and she also wouldn't not show up to work without letting someone know. This is not normal."

She said people who are boaters should be vigilant and share the Coast Guard's search bulletins with family and friends to circulate the message as widely as possible to bring Nathan and Linda Carman home safely.

Hartstein said Carman's sisters are communicating regularly with the Coast Guard, and Hartstein has also been in touch with Clark Carman, Nathan's father and Linda's ex-husband, who now lives in California.

The boat the Carmans were aboard is called the "Chicken Pox" and is described as a 32-foot aluminum center console boat.

Nathan Carman in 2011 was the subject of a multi-state search when he unexpectedly left town at 17 years old and turned up four days later in Virginia.

Grieving the death of his horse Cruise, Carman bought a bus ticket in Middletown and headed south, where he was found by a sheriff's deputy in a small Virginia town. Carman has Asperger syndrome. He had formed an incredibly close bond with his horse and was crushed when it died.

Linda Carman told The Courant in 2011 that she didn't know where her son was headed but that she knew he left home because of his grief. A Virginia police officer discovered Carman near a vacant store, apparently looking for a safe place to sleep for the night. He was carrying two framed pictures of himself and Cruise, and very little else.

Tragedy fell upon the Carman family in December 2013 when Linda Carman's father, John Chakalos of Windsor, was found dead in his home of a gunshot wound to the head. No arrest has been made in the case.

Anyone with information about the Carmans or their missing boat is urged to call the Coast Guard's First District command center at 617-223-8555.

Courant staff writers Christine Dempsey and David Owens contributed to this story.