Deteriorating SONAR signal



The SONAR signal has been deteriorating on our Navnet 3D equipped Safeboat over the past year. Looking at the transducer, it appears to be a brass through-hull model. It is mounted on a flat plate on the transom, and is in contact with our alkaline lake water 24/7. I have put a great deal of effort into tuning the SONAR settings, with no results. I'm thinking the transducer may not be designed to be submerged constantly. I'm thinking about switching the transducer for an Airmar transom-mount model. Am I on the right track here, or is there something else i should do first?
Thanks for your question. When you say the signal has deteriorated do you mean when the vessel is moving or stationary? I have seen these "beaver tails" that they like to mount the transducers on so have a good idea how yours is mounted. I have A couple of questions for you, are you seeing gaps in the bottom when running, if so what frequency are you using at the time, 50 or 200Khz?. Since this is a Safeboat are the looking at another device like a RD-30 or 33 for your digital depth? Does this vessel have trim tabs? I was on one of the Coast Guard RB-M's recently and noticed that changing the trim tab angle effected the sounders performance, that may be worth trying.

The signal has been deteriorating when the vessel is on-plane. Its fine when stationary. It used to get a good signal even at 45 mph. Now it loses the bottom and the depth soon after reaching cruising speed. It does not have trim tabs. Changing from 50 to 200 khz does not help. I'm not sure which model of digital sounder module we have, but there is one.

I had the plate cut off and welded up so I can mount an Airmar P66 triducer. I'll mount it and test it this weekend. All I can do is hope that solves the problem. We've had zero problems with the P66 triducers on our Raymarine equipped vessels over the last 9 years. They get a good signal even at cruising speed. Fingers crossed!