I went with the
TackTick and eventually replaced all the old instruments. They use standard Airmar transducers that are used by most of the equipment suppliers. The advantage of the TackTick systems are you can mount them anywhere on a flat surface or a bracket. They expand easily for future additions (e.g. speed, wind, NMEA interface to other instruments and GPS). The down side is they are pricey.
ps - Congrats on your J/30 purchase. I just sent you an email