JFK and Jackie's Grandson Jack Paddle boards Shirtless Around Manhattan 

President John F. Kennedy‘s only grandson shares his passion for charitable giving — and recently found a very creative way to donate his time to a good cause.

 the son of former U.S. ambassador to Japan Caroline Kennedy

, describes how he recently made his way around Manhattan on a stand-up paddleboard for charity.

“With beet juice pulsing through my veins and electrolytes and Gu packs strapped to my back, I took to the East River to begin the Sea Paddle, a 25-mile circumnavigation race around Manhattan,” Schlossberg, a matriculating Harvard Law student, wrote of the event that raises money for environmental preservation and autism advocacy groups.

Schlossberg said he signed up for the race because he “thought it sounded cool,” and figured, “How hard could it be?”

But despite his training for the event, which began underneath the Brooklyn Bridge, Schlossberg got off to a rough start.

“Before the whistle blew, I accidentally fell in the river trying to make some adjustments to my board,” Schlossberg said, joking, “It’s true what they say: Nothing tastes quite like the East River.”

I paddled around Manhattan! It was really fun and I still can't move my arms. I wrote about it here: https://t.co/SJeZCUxOnH

— Jack Schlossberg (@JBKSchlossberg) August 8, 2017

Schlossberg said he spent much of the race trying “desperately to catch up to three women half my height and weight — but I never came close.”

“This,” he wrote, was “a familiar feeling for a younger brother of two older sisters.” (Schlossberg’s sister Rose, 29, is an actress; his other sister Tatiana, 27, is a

WATCH: JFK’s Grandson Jack Schlossberg: ‘I Love That I Am Free to Say That I Don’t Love the New Trajectory of American Leadership’

Ultimately, fueled by coffee, adrenaline and “Elvis hits blasting in my ears,” JFK’s grandson completed the Sea Paddle in just under five hours, finishing in eighth place in his division.

But according to fans on social media, Schlossberg’s participation in the race — not to mention his shirtless photos — was first-rate.

— Stella Bugbee (@stellabugbee) August 8, 2017

Many JFK Jr vibes from Jack Schlossberg https://t.co/Eh6oYFcny6 pic.twitter.com/yRsYLq0s6D

— Michelle Ruiz (@michelleruiz) August 8, 2017

Praise also poured in on Instagram, where Schlossberg shared photos from the race.

“For charity, very nice,” said another.

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