I put two Humminbird 710294-1 XPTH 14 HW MSI T SOLIX MEGA SI+, DI+, Dual Spectrum Chirp w/Temp Plastic Thru Hull Transducers below the steps in my 88 3100 Open, a "fin" in center of the boat hull necessitated one on each side of the "fin", they go to an Apex 19 FF