We are in the process of purchasing a Navigator Classic. The strange thing is that it two identical transducers (~3" diameter) on each side of the hull and a third smaller transducer (~2" diameter) about a foot to the stern of the starboard transducer. Does anyone have an idea what is going on here? The only display (besides the radar) is the RDP 139. I've seen these configurations on forward looking sonar but don't have a clue what is going on here.