We bought a 1989 Four Winns 215 in Oct 2011 and it came with a Garmin 172. The GPS and depth finder worked fine in the fall but now it's giving me weird readings. When we're moving along at around 5 kts the depth readings look fine but the second we get up on plane it starts reading about 1.8 - 1.5 feet when I know we have at least 10+ feet under us. Any ideas?
