Both had some high-powered teammates - Kate was paired with Team New Zealand skipper Dean Barker while William raced with Grant Dalton, the team's manager and a veteran round-the-world racer.
The royal couple is on a three-week tour of New Zealand and Australia.
It rained again as it has most days on their tour but that didn't put off hundreds of people who gathered on Auckland's waterfront to greet them.
After the racing, the couple took a ride on an amphibious craft called Sealegs, which drove out of the water at Westpark Marina to the delight of the crowds.
The couple plan to visit Hamilton on Saturday.