I have discovered THREE transducers mounted in the bow area of my O'day 25! Last year was my first season with the boat. It's equipped with a Standard Horizon DS30 --- very simple digital depth sounder. Because I was getting lots of weird readings last season, I cleaned the exterior of the thru-hull fitting, sanded lightly as directed, and applied two coats of transducer paint. (I'm hoping the barnacles that were attached to it at the end of the season were interfering with its accuracy.)Here's the mystery: In addition to the unidentifiable brand thru-hull transducer which is currently connected, there's another one (also unidentifiable brand thru-hull -- maybe a malfunctioning old one that was left in place?). The THIRD unit appears to be new. It is an AIR MAR Transducer with no thru-hull. It's flush-mounted with what appears to be 5200. The cable has an RCA-type plug at the end (not connected to anything). I've done a search for AIR MAR, and have not been able to find anything about it. The unit is about 4" x 2 5/8" (shiny part is 2 1/2" x 2 1/2"). The cable is an Air Mar transducer cable #c1...c1 225, and there's a tag which reads: " 280 P52 31-422-1 REV 04.Any thoughts or advice? Should I use this (apparently) new AIR MAR unit?(boat also has mounted a Signet Marine SL80 unit which is not connected to anything (manual says March 24th, 1988) ... Anybody know anything about these guys?