I have an eagle something, it is about 4 yrs old, mounted on the back of my jet boat and I don't have a problem with it not reading at speeds. At least not up to about 35 or 40. What I have found is that if you can mount it lower and into clean water that really helps. I have mine mounted on a plate that I can slide up and down and I have found that mounted up where it would normally be on the transom I do get interference from turbulance but slid down as far as it goes, which is probably about 3/4 to and inch below where it would be mounted on the transom it is fine.