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Raymarine forum - Tri-ducer not reading depth accurately

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I have a brand new sailboat equipped with Raymarine. The Axiom 9 is the MFD and the tri-ducer connected through the iTC5 for my speed, depth and temp. The problem is that when the water depth exceeds 75 ft. the depth display reads -.- and comes back to reading the depth when I'm in under 75' of water. My dealer got a new tri-ducer for me to field test but I got the same results. I have not had a chance to field test a new iTC5 yet.

What am I missing? Everything that I read says that it should be good to 100 meters in depth. Is there a setting on the i70S or the Axiom that I'm missing?
Hello L'Attitude,

The depth specifications that you'll see for sounders or transducers are usually maximum/ideal rather than normal performance (for example, I usually recommend halving the specified maximum depths of fishfinders for good real-world fishing performance), and the sounder specs of course don't take into account the specific transducer used and vice versa.

That being said, 75' does sound a bit shallow, so perhaps something else is going on in your case. Sounder performance is a function of the signal-noise ratio (lots more info here), so if you have the same result with two transducers then perhaps you have a slightly higher than normal background noise level on your boat (at 200kHz, not at audible frequencies) which is making it hard for your system to pick up the echoes from the noise. Common causes are hull vibration (at the transducer location), ultrasonic antifouling systems and interference from vessel electrical and engine systems. It is, however, very hard to measure/diagnose this sort of thing with a plain digital 'instrument' depth like yours, which is one reason why here in Australia we prefer to suggest fitting the transducer to the MFD rather than to an instrument. The pricing works out about the same, but you have more power, better depth performance and a lot more options to diagnose and work around problems. I'm sorry that that didn't happen in your case.

Regards,
Tom
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