Tens of thousands of people lined Casco Bay’s shorelines Saturday afternoon to watch a parade of tall ships, the highlight of a four-day festival celebrating the time when large sailing ships routinely plied Maine waters.

The 13 ships gathered off Portland Head Light in Cape Elizabeth early in the afternoon and then spent two hours sailing into Portland Harbor, where most tied up Saturday night. Many will be open for public boardings Sunday and Monday, and the festival offers opportunities to learn more about the ships, listen to concerts and eat along the waterfront.

Organizers said they expect up to 100,000 people to attend at least part of Tall Ships Portland 2015, which ends Monday night. Portland and South Portland police said they had no estimates of the turnout Saturday, but Patricia Lock, director of special projects for Tall Ships America, said she estimated 7,500 to 10,000 people lined just the Portland waterfront.

The ships’ crews told her “it’s a rush to see so many people come to see you come in,” Lock said. “It’s a rush for me, too.”

City officials also said thousands watched from Fort Allen Park in Portland and on the path that runs alongside the Narrow Gauge Railroad tracks on the peninsula’s east side. There was also a large crowd on the South Portland shore, where police said the number of viewers was larger than expected and they created a traffic jam when the parade of ships ended at 4 p.m.

Cape Elizabeth’s Fort Williams also drew thousands and most of the parking spaces were filled by late morning.

Portland officials, who hope to draw the tall ships back again in a few years, said the enthusiasm was encouraging.

“This is our heritage, this is what this city is all about,” said Mayor Michael Brennan.

The event was grand in scope, with large ships like the Coast Guard Academy’s gleaming white barque Eagle and El Galeon Andalucia, a dark-hulled reproduction of a Spanish galleon, leading the parade under sail, at least initially. By the time the ships reached Portland Harbor, however, most respected a Coast Guard recommendation that they lower their sails and operate under power. Coast Guard Command Duty Officer Ken Stuart said the base in South Portland made that recommendation to ensure safer navigation as dozens of powerboats, sailboats and even kayaks swarmed around the larger sailing vessels.

Crowds began gathering even before rain showers ended in late morning. It was cloudy and relatively cool Saturday, but remained dry for the rest of the afternoon events.

The weather didn’t deter people like Scott and Jackie Sawtelle of Yarmouth, who were so impressed with the Saturday’s parade that they plan to come back to Portland on Sunday to tour the ships up close.

“They are all so very different, so I would be interested in all of them,” Scott Sawtelle said.

The Sawtelles planned their day on Saturday to see the parade of ships from two of the best vantage points, first from Fort Preble, next to Southern Maine Community College in South Portland, and then from Fort Allen Park in Portland, which they said gave them a broader overview of the event.

From Fort Preble, which overlooks the scenic Spring Point Lighthouse, they were able to see the stretch of water where most of the tall ships were moving under the power of sail as they rounded Cushing Island and then sailed past Willard Beach.

“The view was fantastic, especially when they were coming around the island,” Scott Sawtelle said. “You were able to see both sides of the ship.”

The Sawtelles said they knew the area well because Scott Sawtelle graduated from SMCC in 1984 and they visit the campus and the fort frequently.

“We actually love to go there. That is one of our favorite places,” he said.

The couple then crossed over the Casco Bay Bridge into Portland in time to see the tall ships again.

Jackie Sawtelle said she was happy to see so many people out enjoying the festival.

“This is awesome. It’s really bringing Greater Portland to the forefront. The events that we’ve been having here really put us in the world class, in my opinion,” Scott Sawtelle said.

Jim Flagler and Thurl Headen of Peaks Island also said they would return to the mainland Sunday.

“The galleon, we obviously want to do that one,” Headen said.

The event also created crowds in downtown Portland, something that cheered Peter Cordice of Standish, who was rapidly selling his ceramic coasters with pictures of iconic Maine scenes on them from a cart at Market and Commercial streets.

“There’s an exceptional amount of people in the city today,” he said. “It’s fantastic.”

But most others were pleased with the spectacle beyond its commercial possibilities.

Greger Anderson, 70, of Harpswell brought a high-powered telescope that he more frequently uses for birding to be able to get a close-up view of the ships.

“This is what it would have been like 150 years ago when the whole harbor was filled with ships of this sort,” he said, watching from the Eastern Promenade.

Ron Koster of West Virginia, who spends his summers at his second house in Windham, had a camera on a tripod at the end of the railing in Fort Allen Park, ready to take pictures as the ships arrived.

“I just thought they’d come down the channel and this would be a good location,” Koster said.

Koster said this was his first time at a tall ships festival. He came with six other family members after reading about the schedule of events in the newspaper.

“I figured it would be crowded, but this isn’t as bad as I had anticipated,” Koster said. “We’re going to walk around and sightsee a little bit (after the parade) and then head back to Windham.”

Koster said his family planned to return to Portland on Monday for a ship tour.

Diane and William Tyler, who recently moved from Cape Elizabeth to South Portland, said they scoped out the best spots in the region in advance to pick which one would be best to watch the ships.

“We checked them all out. We had anticipated parking. This looked like we would have no problem,” Diane Tyler said when their chairs were situated at the highest point atop the hill where Fort Preble is located.

William Tyler said they walked along Spring Point during their scouting trip, happened to look up toward Fort Preble and realized the spot was ideal.

“We just think this view is so special, tall ships or not,” William Tyler said.

Others were taken by the sight of all the smaller boats scurrying about the larger sailing ships.

“Controlled chaos, that’s what I see,” said Patrick Williams of Cumberland, who watched from Fort Allen Park in Portland.

The last time the tall ships visited Portland was in 2000, but organizers said if it’s successful this year, they hope to get the ships to return in 2017 and then every three years or so. This year’s event will cost about $500,000, covered by ticket sales to the festival, which is being run by a nonprofit called Sailing Ships Portland.

Staff Writer Edward D. Murphy contributed to this report.