I installed a new GPS/fish finder in my Hobie Outback, everything is working great except the transducer is not reading thru the hull. I install it using a foam cut out to set the transducer in. The cut out is seal to the hull with marine goop. Then I filled the center of the cutout with clear vaseline. Set the transducer into the vaseline and set it down to remove any air bubles or voids between the transducer and the hull. However when I tested it in water I did not obtain a depth reading or fish location. The GPS device is working outstanding. I have used this process before installing tranducers in fiberglass bass boats and everything operated properly. Question is the keel on the OutBack solid poly material or is it hollow between the hull and keel. If it is hollow or solid thick ploy keel this would be the reason for non depth/fish reading. Does about the keel structure. I do know my transducer is operating proper I test in water.