Brian Keaulana and Kathy Terada believe that nothing can get old in the ocean.

That's a big reason why — at a combined age of 101 — they are the defending world champions of tandem surfing.

"The ocean is a fountain of youth," said Keaulana, 46. "You can always have fun, you can always learn something new in the ocean. It doesn't matter how old or young you are."

Keaulana and Terada — who are both from Makaha — will defend their world championship at the World Title of Tandem Surfing this week at Kuhio Beach, Waikiki.

More than 20 tandems from around the world are expected to participate in the four-day event, which is scheduled to start today and finish Saturday.

In the sport of tandem surfing, the male surfs on an extra-large board, and then hoists the female into various artistic and acrobatic poses while surfing the wave.

It's not as easy as you think.

"We definitely have experience on our side," said Terada, 55. "But I'm also not as flexible as I used to be. Some moves that I see the young girls doing ... don't even ask me to try that."

Last year at Kuhio Beach, Keaulana and Terada upset many of the younger tandems to win the world title. Keaulana admits luck played a role in their victory.

Keaulana and Terada have been tandem partners since 1984. In essence, they had been performing the same maneuvers for more than 20 years.

But last year, they tried some new moves — much to their own surprise.

"We basically didn't practice before that contest," Keaulana said. "And when we went down there and saw all these girls who were ex-cheerleaders and gymnasts doing all these hard moves, we knew we had to do something new."

Keaulana said he and Terada practiced the new moves on the beach moments before the contest, and then pulled it off in their heats.

"Being a good surfer is great, but being a lucky surfer is even better," Keaulana said with a laugh. "We were fortunate to catch some of the better waves, and then we completed the moves we needed."

The success of last year has spurred changes this year.

Most significant, Keaulana and Terada have actually practiced for this week's contest. Not much practice — maybe once a week, when their schedules allow — but at least it's more than in years past.

"There are so many new teams, good teams," Terada said. "And they're coming up with all these new moves, so we have to practice just to keep up."

As world champions, Keaulana and Terada also got invited to several tandem surfing contests around the world in the past year. They competed in Japan, California and Australia, and will travel to Spain next week.

"We never traveled before," Terada said. "But because we won last year, all these sponsors paid for us to travel to these contests. It was really fun to see that happen after all these years."

Keaulana and Terada said much of their success can be traced to their friendship.

"Our families have known each other forever," Keaulana said. "Kathy is the one who set me up with my wife."

Keaulana added that having a surfing-only relationship has also been a key.

"Most of the tandems are couples, either married or boyfriend-girlfriend," he said. "We're just friends, so we practice, do the contests, and then go home to our own families. I think that's why we've been able to stay partners all this time."

The tandem surfing contest is part of the Duke's OceanFest. Several other events are scheduled for this week at Waikiki Beach, including a women's pro longboard surfing contest, a stand-up paddle surfing contest, a paddleboard race, a beach volleyball tournament and a swimming race.

For more information on the OceanFest visit http://dukefoundation.org.

Reach Dayton Morinaga at dmorinaga@honoluluadvertiser.com.