The GPS on my buddy's boat is no longer calibrated and after discussions with the maker's tech person, no luck. The sonar works fine. I have GPS coordinates for brushpiles on Lake Austin. If I buy a small, handheld GPS unit, will it work well enough for us to locate the brushpiles? I am very "low tech", don't know a thing about how well or poorly they work. Will appreciate your advice.

Good question , depending on what units you have on the boat and what unit you buy as a hand held , it's a toss up if it could work . If both have a compatible SDcard , I would think the operating system would need to be from the same company . I have a Hummingbird Helix 7 , and a Garmin handheld GPS ---they are not compatible at all . Furthermore , there is a huge misconception generated by the fish finder companies . Accuracy of these GPS systems is far less than they are tying to make people believe. Commercial systems are only accurate up to plus/minus 3 meters ( 9 feet of variance best case ) . Commercial systems use a specific set of satellites and can not be as accurate as Government /military GPS coordinates. Government and military systems use a different set of satellites and are accurate to plus/minus 2 to 3 centimeters ( less than 1 inch ! ) . If SD Cards and maps are generated by Government systems , they are the most accurate , anything generated using commercial GPS satellites , not nearly as good.

Thanks for the reply 1oldbassguy. Appreciate it. Guess a handheld doesn't sound very helpful. I was assuming that I could enter a GPS coordinate into one of these things and then follow a line from my location to the spot. Not that simple, huh?

You can use your hand held to get you to the locations + or - 20 feet and then use your sonar to get in your exact spot you had previously marked with the fish finder. Get a good handheld gps that excepts sd or micro sd cards. Then you can use your handheld and average several readings. A good gps like the garmin 62s can do this for you and then you can save this way point for your next fishing trip and you will be all good. Plus you can use the hand held for loads of other stuff.