This question has been asked a fair few times now.
If its for windsurfing the majority of people here will recommend a Navi GT-31. A few will recommend a Garmin. I use a Navi GT-11 and its been working well for the last couple of years. There is plenty of support for the Navi. This is important when setting it up as its all a bit confusing at first.
OK, cool write-up. What if I wanted a nuit that would do windsurfer speed and logs, but I also wanted to use for general navigation ? I'm thinking ahead to my polar stuff here, for which I need to develop navigational proficiency as well as maybe bush mountain biking etc.