One of the perks of hanging out on the Portland waterfront during an outdoor concert is that you don’t have to be a paying customer to enjoy the music.

As the opening act of the Portland Reggae Fest boomed out from the Maine State Pier on Sunday afternoon, passengers aboard Casco Bay Lines ferry boats got a front row seat for as long as it took to board or disembark.

The ferries, schooners and other harbor traffic provided a nautical backdrop for the latest in a series of summer concerts on the pier. An hour into the nine-hour-long festival, hundreds of people of all ages had already piled onto the pier.

“We are thrilled. We love it,” said Emily Davis of Mount Desert.

Davis said she and her children, Isaac Steiner, 12, and Asha Steiner, 9, won tickets to the concert. They were debating just how long they would stay.

The concert featured a definite Rastafarian motif. Concert-goers were dressed in Rastafarian green, gold and red, wore tie-dye shirts and sported dreadlocks. The odor of burning marijuana wafted through the crowd.

Food kiosks sold rice and peas, plantain chips and other Caribbean delicacies while other vendors offered henna tattoos and Rasta-style hats. Shop Chronic, a retail operation started by two Maine entrepreneurs offering a line of products designed for the “cannabis lifestyle,” rounded out the Rasta theme.

Organized by the city of Portland and Waterfront Concerts of Bangor, the concert was one of a number of oceanside concerts this summer that some say is a sign that demand for outdoor music is on the upswing in Maine.

Reggae Fest is one of five concerts that Waterfront Concerts of Bangor has been involved in organizing on the Maine State Pier this year, including Alanis Morissette on Aug. 23 and ZZ Top on Sept. 27.

Concert promoters point to the success of the Mumford & Sons concert on the Eastern Promenade in 2012 that drew 15,000 fans.

Thompson’s Point developers have said their Portland development would include a venue capable of accommodating as many as 5,000 people.

Other cities, such as South Portland and Westbrook, have eyed the possibility of developing waterfront concert venues, but so far no concrete plans have emerged.

The hundreds of people who showed up at Sunday’s festival were a sign that live dance music seaside will draw a crowd on a sunny summer day.

Tai Choo of Brunswick brought his 5-month-old son, Mateo, to the concert. Choo said he grew up attending outdoor concerts with his parents in California.

“Now I want to carry on that tradition,” he said.

Kevin Keene and girlfriend Angie Haskell, both of Hallowell, said they are big reggae fans. Keene, dressed in a lime green and yellow tie-dye shirt, and Haskell, wearing a pink and blue tie-dye blouse, said when they heard about the festival, they knew they had to attend.

“It was either the beach, the boat or the reggae concert,” Keene said.