I am having a problem getting a reading on my new Garmin 240 Blue depth finder. I mounted the transducer in the same spot that the old one was mounted (inside the hull). The old tranducer was 200 watts and the new one is 500 watts. In spite of this I can't get a reading. When I hold the transducer overboard I do get an accurate reading. I contacted Garmin Technical Assistance and they asked what kind of core my boat has. The boat is a 1991 Sea Ray 270 Sundancer. Does anyone know the type of core in this boat. <br />Thanks.