"We thought there's a bit of potential there," Robbie Manson said.
At 24, a year older than his brother, Manson was in the boat for last year's campaign with Michael Arms.
Things were flying along, with wins at all three World Cup regattas, before Arms picked up a back injury.
They went to the world championships in Korea but finished last. It was a cruel blow, after such a fine season.
"We almost surprised ourselves, especially in Sydney [the first World Cup last year]," Robbie Manson said.
"It was our first race together and we got stronger from there through the cups. We came home for a few weeks before going to Korea and that's where Mike's back started playing up, and just got worse."
At the national trials last summer, the selectors chose four scullers - the Mansons, Arms and Giacomo Thomas - to undergo a second trials run. That was a step too far for Arms, whose back played up again, opening the door for Karl Manson.
So how similar are the brothers, who live together?
"I'm older and the boss," Robbie quipped. "Karl is more the muscle and I'm the brains. But we are quite similar ... we're built quite similarly and row in a similar way."
Karl began rowing first, around 14; Robbie, who was initially into horse riding, was tempted to try. The brotherly competitive streak ensured he didn't want his kid brother to be better or stronger than him.
There is rowing in the family. Their father Greg competed in the lightweight singles at the 1985 world championships in Germany; mum Kaye coaches at St Margaret's College in Christchurch.
While Karl got over illness in 2011, Robbie competed at the 2010 and 2011 world champs and was seventh in the quad at the London Olympics.
Arms' misfortune is Karl's good luck. Perform strongly this year and they'll have the inside running when next season's trials take place.
"There's a lot of good doubles out there," Robbie said. "We've done some really good times in training, everything's going well but until you get to measure up against everyone else, you have the same expectations as everyone."
• Lightweight double sculler Julia Edward will contest the single seat event in France this weekend.
Her partner, Lucy Strack, is still back in New Zealand, battling form issues. A decision on whether she will join the squad for the third World Cup in Lucerne next month is due shortly.