Thousands of spectators waited hours to board Tall Ships from around the world that were berthed around Boston Harbor on Sunday, but among the captain’s cabins, sails, and sterns, one non-nautical attraction stole the show: a cat named Pilar.

The 8-month-old feline, who some deckhands agreed might be the real captain of her ship, The Spirit of South Carolina, attracted clusters of kids as she lounged on the main deck. Sophie, 7, who was visiting the Sail Boston attraction with her family from Framingham, explored the ship for a while before deciding that Pilar was one of her favorite parts.

Though not every vessel had a resident cat on board, the ships’ traditional features also amazed visitors like 7-year-old Hunter from Boston, who couldn’t believe that old ships used to have as many as seven anchors on board in case one of them didn’t work.

The Spirit of South Carolina was one of the 51 ships docked around Boston Harbor after parading into town on Saturday morning, when thousands of spectators watched from sites including Castle Island, East Boston, and the Charlestown Navy Yard. Sunday was the first day many of the vessels could be publicly boarded, and visitors from around the world gathered to be passengers on the ships, if only for a moment.

“I liked seeing how old the ships are,’’ said 10-year-old Sameer, who was visiting with his family from Acton. After exploring the pier, he said he wondered how all the older ships in the parade were built before having access to the modern technologies of today.

However, Sameer never made it on the vessel he and his family had waited 40 minutes to see: El Galeon from Spain, berthed at Fan Pier.

El Galeon, a 164-foot vessel that has covered more than 48,000 nautical miles between 2010 and 2016, drew one of the largest crowds, not because it was the biggest ship but because it was, as many spectators referred to it, “the pirate ship.’’

Children, grandparents, and everyone in between waited to board El Galeon, where lines formed at the ship’s entrance and extended along the edges of the pier. Waiting in the unexpected sunshine was as much a part of the day as actually getting to board the ships.

To board, visitors had to endure two separate waits — first, to get through security, where they were electronically wanded and had their bags searched, and then to stand in each ship’s individual boarding line, some of which were longer than others.

Once they made it on board, though, visitors agreed that El Galeon was worth the wait, which ranged from 40 minutes to an hour Sunday afternoon.

“It’s really amazing that this ship has sailed so far, and all of its history,’’ said Somerville resident Nathan Zieglar, 30. “It’s so cool to think about how many people have lived their lives on here.’’

Once on board, passengers visited the upper levels of the ship to see the wheel and several sealed chests.

“Is there gold there?’’ one of the ship’s smallest visitors, 5-year-old Declan, asked his dad, wide eyed and pointing to the biggest chest he could find.

Though she made her voyage on an entirely different ship, Shanna Linn, 61, felt a similar sense of wonder when she sailed into the harbor Saturday morning on the Harvey Gamage, which is berthed at Charlestown Navy Yard Pier 4.

Originally from rural Pennsylvania, Linn said she didn’t even know anyone who had been on a ship growing up. Now, she has sailed around the world as a cook for the ship’s passengers.

“It was incredible — the response from the crowd, the music, and seeing all the other boats,’’ she said.

Before the parade, Linn wasn’t sure that entering the harbor would be smooth sailing — the weather was choppy, the sea was rough, and one passenger was suffering from seasickness for hours at a time — but after waiting it out, “God intervened and gave us this,’’ she said, gesturing up to Sunday’s blue sky.

Now, seasickness can be forgotten for a few more days. The vessels will remain at their designated berthing areas in Charlestown Navy Yard, Rowes Wharf, Fan Pier, and more until Thursday, when the ships will depart Boston Harbor and the majority of the vessels will continue on to Canada.

Boarding the ships was just one of Sail Boston’s attractions throughout the day; other events included the Patriot Run, the Sail Boston Worship Service, and the Massachusetts Fallen Heroes Memorial Wreath Laying.

Braintree resident Alice Potenza said seeing the number of people come out to Fan Pier on Sunday was incredible, because she remembers when the area wasn’t nearly as developed as it is now.

“I’m thrilled to see so many people; I’ve never seen this many people out here,’’ she said, looking around at the masses of spectators enjoying the pier and the Public Green. “Even walking down the street, you hear so many different languages because of all the people that came for this.’’

Kiana Cole can be reached at kiana.cole@globe.com. Follow her on Twitter at @kianamcole