I mounted my Helix 7 SI Ducer on the transom of my 1652 boat. I was unable to achieve the recommended 15 inches from the lower unit. I was only able to achieve 12 inches without going to the extreme outside rear right corner. I just trim up a little bit and it works fine, if motor is all the way down I lose most the left SI. It's not an issue for me since I can only cruise up to 4 - 5 mph before I lose my image on screen. Just like cray said try to center in between those two runners below the plug in picture, it's all you can do on a narrow boat.