Always up for a challenge, America’s Cup champion skipper Jimmy Spithill will trade the thrill of speeding across the waves of San Francisco Bay at the wheel of his high-performance catamaran for the hard work of paddling from one Hawaiian island to another.

It’ll be just Spithill and his board — and 32 miles of open water — in the Molokai-2-Oahu Paddleboard World Championships on Sunday.

The 34-year-old Australian definitely will have to downshift from the catamaran, which can sail faster than 50 mph, to paddling at 4 to 5 mph.

“It’ll be a lot slower than what I’m used to,” Spithill said in a phone interview. “I won’t have any of the big grinders to do any of the work for me, unfortunately.”

Spithill said he and fellow Oracle Team USA sailors Matthew Mason and Shannon Falcone took up stand up paddleboarding (SUP) about a year ago and have done shorter races at Lake Tahoe, in New Zealand and on San Francisco Bay.

“We really like it a lot,” Spithill said. “You’ve got to have great core strength and a high heart rate. It’s something to do on the weekend, another activity where it’s competitive and you’ve got to push yourself. Obviously, this race coming up Sunday is like nothing I’ve done before.”

Spithill can take a weekend away from sailing because as defender, Oracle Team USA’s first race isn’t until Sept. 7, when the 34th America’s Cup opens on San Francisco Bay.

But it won’t be a break from physical activity.

The 72-foot catamarans are demanding to sail, requiring young, athletic sailors who can handle the non-stop action. All but three of the crew have to grind, or turn the winches that raise and lower the daggerboards that the cats ride on when they’re flying downwind.

The skipper has to be in great shape, too, for the mad dashes across the trampoline, or deck, during tacks and gybes.

Spithill is one of 70 entrants in solo SUP in the Molokai-2-Oahu race. A total of 275 paddlers are entered in various categories in the race, which is presented by Kona Longboard Island Lager.

“It’s going to be a really tough challenge, but to be honest, I’m looking forward to it,” Spithill said. “It’s a big mental test but that’s just another good way for me to test myself and push myself a bit six to seven weeks out from the Cup.”

Spithill has participated in other sports and activities, but likes to apply any lessons learned to his sailing.

He’s boxed in the past, and before the 2010 America’s Cup, he got his pilot’s license in order to better understand the radical, 223-foot wing sail that Oracle BMW Racing used to power its giant trimaran. It paid off as Spithill, then 30, became the youngest skipper to win the oldest trophy in international sports.

“You can step away from it, but there’s things you can relate to,” Spithill said. “I find it’s where I get my ideas. We’ve been around some high-class athletes and great watermen, and just talking with them will trigger ideas.”

Team Oracle USA has taken people from different sports out onto the water, from San Francisco Giants manager Bruce Bochy to four-time Olympic gold medalist Michael Johnson, who fell off a 45-foot catamaran during an America’s Cup World Series race last summer.

Watermen have also gotten to hang out with the Cup champs.

Windsurfer Robbie Naish visited Oracle Team USA’s base on Pier 80 a few days ago.

Laird Hamilton, the big-wave surfer who has a line of standup paddleboards, went sailing with Oracle on a 45-foot catamaran last summer.

“He and I have been talking about paddleboarding,” Spithill said. “He’s a great guy. We shoot messages back and forth to each other.”

Earlier this month, kite surfer Kai Lenny visited Oracle Team USA and then raced the 72-foot catamaran from the Golden Gate Bridge to Alcatraz Island.

“He put up a good fight,” Spithill said. “It was an awesome race. It was cool for him just to come down. He’s got his surfboard and kite, $1,500 worth of gear, and we’ve got a $15 million boat. It was good to see two extremes.”

After some friendly smack talk, Lenny got off to a big lead, but was quickly overhauled by the catamaran, which is powered by a 131-foot mainsail that looks and performs like a jetliner’s wing. Once the cat got up on its hydrofoils, it was over.

Lenny is entered in the Molokai-2-Oahu race.

“He’s one of the favorites,” said Spithill, who’s hoping the wind will be at his back the whole race. “He’s the ultimate waterman and someone who I’ve become good mates with. I’m not going to be fighting for the podium. My goal, as always, is just try to push myself a bit and learn a bit about myself.”