We have built the Rip Curl SearchGPS 2 & 3 watch specifically to track surfing.
But you may find it very useful for a variety of water sports.
The SearchGPS3 watch can track a variety of sports using the OTHER feature. Track your other activities including walk, run or ride, as your watch connects to satellites orbiting the earth. Currently, these non-surf activities can be synced with the iOS or Desktop app, but can only be viewed on the SearchGPS website.