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In April of this year I installed an I70 System Pack (Wind Depth and Speed) along with an I70 Multi-functional Instrument Display and an ITC5 converter on my sailboat.

The speed and temp readings are good. The depth is not. Sometimes the accurate depth is shown on both Multi-functional Instrument Display and the chart plotter. Sometimes the depth readings bounce everywhere from 0 to high numbers on the Multi-functional Instrument Display. On my chart plotter the reading will be 6554 ft when the Multi-functional Instrument Display reads zero or close to it when we are in 30 feet of water.

I checked and made sure both the Multi-functional Instrument Display and ITC5 have the latest software packages and they do.

Any thoughts?

Langley Gace
Welcome to the Raymarine Forum Langley,

Should the vessel be equipped with more than one sounding device, then it is possible that the transducers are interfering with one another. If all third party equipment and the chart plotter is switched off, does the i70 then correctly report depth?
Thanks Chuck,

The boat does have my old transducer but it is completely unplugged. I left it in there as a back up if I ever needed it but it has no power and is not connected to anything. I did call your tech support line while waiting for this post to get uploaded to the forum. Your colleague suggested I unplug the bare (ground) wire coming from the transducer to the ITC5. He said sometimes noise comes for the ground. He asked me to see if that clears up the problem but to also watch my temp and speed to make sure they are still behaving.

I will follow your suggestion and turn off all instruments and the chart plotter to see if that clears up the issue before unplugging the ground.

Sound like a plan?

Many thanks for your support.


The recommendation to test for noise via the ground is sound.
Hi Chuck,

Took the boat out for a test as prescribed above today. I disconnected the ground on the ITC-5. For our 95% of the 40 minute test the depth read true readings. There was about a minute at 70 feet where it had strange readings (0, or close to it on the I70 MFD and 6554 ft on the Ray Marine chart plotter. These erroneous readings on the depth were similar in nature to the readings I had with depth when the ground was attached. Other than that odd minute or two the depth behaved.

The temp behaved the whole time but the speed and thus the true wind speed did not. The speed stayed at 7 kts +-0.2 kts the whole time. I had my SOG on and it behaved giving me the readings I should expect. At the dock my SOG read 0 and my speed through the water read 7 kts.

As expected my true wind on the I70 MFD gave erroneous results while my apparent wind on the I70 MFD and the ground wind on the chart plotter gave what I believe to be good results.

Next steps?

Many thanks in advance,


Did you calibrate the speed transducer via the i70 MFID? How many points of calibration did you use, and what speeds did you use.
Hi Chuck,

Sorry the for the delay in replying. Business trips get in the way of sailing. I re-calibrated the speed with 5 SOG points at slack tide. The result was good and the speed readings were in line with SOG. I looked at my calibration table and noticed a multiplier ranging from 1.53 - 1.64. Hope this is normal.

Now that all is working am I good to leave the ground wire not connected to the ITC-5? Is it grounded through the SeaTalk connection?

I will be on the 3 day labor day cruise this coming weekend and will really test the system.

Many thanks for your support.


As the system appears to be functioning properly now, it is recommended that no changes to the transducer's ground lead at this time.
You're welcome.
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