Absolutely! I use the GPS in my finder, but a handheld works just as good. What takes from the accuracy of GPS is terrain and view of the sky. When you are on a lake, your horizon is almost always well above the GPS's lower limit (usually 15-20 degrees). You can typically get an accuracy of less than 10 feet on a lake, that translates into very accurate speeds. I have checked mine against the speedo in my car and it is spot on.