Read reviews for the PH-40 (GPS) by Delorme as submitted by your fellow paddlers.
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I've used this GPS for about two months while kayaking. Although I am only using the very basic functions it works great. If you want to track where you have been or decide the correct route to take no problem. Speed (ave and current) and distance traveled are at you finger tips. I designed a mount that sits on my spray skirt so I can read while paddling. Support has been great, I have called a few times and they have always answered my questions. Only cons, can't read with sunglasses and the neck strap should be longer.