Xiamen is an island, but it's surprisingly difficult to find sailing and other water adventures here.
If you're interested in kitesurfing, head to the 59 Fly Kiteboarding Centre (59fly.net) at Haiyuntai Beach. It's IKO certified, and instructors do their best with limited English. The Xiamen Sailing Club (xsailing.com.cn) offers windsurfing and sailing classes and equipment rental. If all that seems like too much work, just go for a beach stroll and take in the sea breeze.