I recently purchased a Humminbird Helix 9 SI GPS. After registering my device, I gained access to HumminbirdPC, which allows you to add waypoints offline and move them to your unit. A quick Google Search turned up the GPS locations for the natural reefs on Lake Winnebago, WI as well as the GPS locations for the artificial reefs on the lake (will download a file).
However, once I started putting the coordinates into HumminbirdPC, I noticed that they were off. They were going to locations in China. If you have this same problem, this video covers how to fix it.
Posted in Fishing Hacks & How To's