Paddleboarding has proved so popular that a year after introducing the sport to its customers, the rental shop at Black Hall Marina in Old Lyme has doubled its fleet to 12 boards but still sometimes have trouble meeting demand on busy weekends.

"We just couldn't keep up," said Nick Chmiel, a member of the family that operates Black Hall Marina. "They're just very, very popular, especially on the weekends."

After adding paddleboards to a rental fleet that already included kayaks and canoes in 2013, Black Hall doubled its inventory from six to 12 in 2014.

It's the same at Three Belles Marina on Smith Cove in Niantic, where Evan Thompson said paddleboards are usually the first thing to sell out on Saturdays and Sundays at its rental shop.

"Everyone wants to try it," said Thompson, explaining that people of all ages and physical agility have rented at Three Belles.

"There's no typical customer," he said. "We get 60-year-olds and mothers with 9-year-olds. Every type of person has come in to try it and everybody loves it. Most people come back. We get a lot of repeat customers."

All along the shoreline and inland on lakes and ponds, paddleboarding is growing in popularity.

Over the past several years, the sport that was first popular on the West Coast has been seeing a surge in southeastern Connecticut and southern Rhode Island.

"It reminds me of windsurfing in the '80s," said Eric Kronholm, of Riverdog Kayak Rentals in Mystic. "It's a huge sport that took a little time to catch on."

Kronholm said for a minimal investment, about $1,000, a person can get a paddleboard and be on the water.

"It's a cheap way to get out there, and be off Misquamicut or on the Mystic River," he said. "It's kind of a mix between surfing and windsurfing."

While kayaks are still popular at all the rental shops, the vantage point is slightly better from a stand-up paddleboard, said Linda Montgomery, who was out paddleboarding in Stonington Harbor on a recent weekday.

From upstate New York, the 24-year-old Montgomery was visiting the region with friends, and they borrowed the paddleboard from a neighbor of the relative they are staying with.

"When you're standing up, it's just a great view," she said. "You can really enjoy the coastline and see all the other boats."

Jason Bowdman, 26, who was with Montgomery, said he had been on a paddleboard before on a lake in Vermont, but never in saltwater.

With a stiff breeze blowing in the harbor the day they were out there, Bowdman said it was slightly more difficult, but not impossible.

"When you're paddling against the wind and maybe the tide, too, it's a great workout," he said.

The experts say that paddleboarding is a full-body workout that enhances core strength and works the upper arms and shoulders.

Most paddleboarders start on their knees and then stand up. A key is to balance with your hips, not your upper body, experienced paddleboarders said, and to look at the shoreline, not down at the board or your feet.

Knees should be slightly bent, and toes pointed forward. To propel yourself, grip the top of paddle with one hand and use the other to dig the paddle trough the water. After about five or six strokes, switch sides.

"It's not very hard, but you do need a good center of balance," said Chmiel. "We typically launch from the dock and start people on their knees. Then they get up, one leg at a time. ... If you're paddling right, you really feel it in your core."

At Three Belles, Thompson agreed paddleboarding is an excellent workout and said after a couple of hours on the water, customers return marveling about working their core.

While people who rent kayaks tend to sightsee, go fishing, or take photographs, paddleboarding is more about exercise and seeing the views, said Bowdman, who hails from Syracuse, N.Y.

"After this, I won't need to go to the gym today," he remarked, after paddleboarding in Stonington Harbor.

Kronholm, of Riverdog Rentals, said more and more people are also practicing yoga on paddleboards, combining the two exercises.

"I have friends doing paddleboard yoga in Maine all the time," he said.

While paddleboard sales have surged - Black Hall sold all six of its boards at the end of last season and plans to sell the dozen it has now when this summer ends - some people still prefer to rent them, so they don't have to worry about storage and transportation.

Thompson said he has one regular customer who comes in almost weekly because he wants to avoid the hassle of storing the board.

Most paddleboard owners have to invest in a roof rack for their vehicle, as well as the board, which can range in price from $800 to $2,000.

Also gaining in popularity are inflatable boards.

At Three Belles, which sells new paddleboards as well as renting them, Thompson said sales have picked up a well as board rentals.

"It's just real popular right now," he said.

a.baldelli@theday.com

Twitter: @TheDay_Ann