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Stuart Malone

Mixing old transducer with modern chart plotter?

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I have an older cruising sailboat with a simple depth finder and no chart plotter. The transducer for the depth finder has a simple RCA (2-wire) connection to its display.

Is it possible to use a transducer like this with a modern chart plotter/sounder like the Garmin GPSMAP 741xs? The simplest sonar input on the back of the GPSMAP is 8 pins, so I'm doubtful, but can't find any solid information from Garmin.

I'd rather not mess with replacing the transducer as long as it's still working. It's installed on a custom wood/bronze through-hull fitting that would be a major job to replace with a modern fitting.

And in a related question, if I can't use the old transducer with the new chartplotter, would it still be worth getting the 741xs instead of the 741 so I'm prepared for the day the 70's-era transducer finally dies and has to be replaced? We not really fishing, just trying not to touch bottom. :)

15 Replies

  • Hi Stuart,

    You need to be very careful when mixing and matching depth instruments and transducers. Depth sounder manufacturers match the transducer characteristics to the depth sounder transmitter and receiver. The algorithms to reject surface clutter, double bounce, thermoclines, fish schools, handle soft and hard bottoms and other parameters are closely tied into the transducer characteristics.

    In addition to different frequencies, transducers vary in the size of the element (power handling ability), beam width, capacitance, resistance, transmit and receive sensitivity, ringing, etc.

    You may think that the old transducer works OK only to find that under other conditions it will cause the depthsounder to provide false information or work poorly, if at all, when heeled over, etc.



  • Even depth transducers made today only use two wires (more maybe if the device also measures water temp). The so called "swinger" is completely dumb and requires intelligent electronics somewhere that generates a ping and times the response to compute the water depth.
    This feature is included in many (often smaller) chartplotters. I have a Simrad NSS7 which does this exact thing for me (it's part of the reason why I have the NSS7 as I don't use it for navigation).
    I bought a special cable form Simrad fitting to the connector on the NSS7 and with bare wires on the other end and a wiring diagram.
    I had to select the model of depth transducer in the NSS7 before I got accurate temperature readings but the depth was on the point even with the wrong model selected.
    However, all drivers of depth transducers are not equal, apparently. When we went through the Smalandsvarvandet in Denmark last summer, the NSS7 lost contact with the ground repeatedly and for longer periods. This was worrisome because this is an extremely shallow body of water and we had multiple soft ground contacts.
    I have no proof but think that my old Robertson driver electronics would have worked OK in that same area.
    So I will try with the other alternative to your problem, which is an Actisense DST2 that drives a depth sounder and also a paddlewheel log and a temperature sensor and convert everything to NMEA0183 (not NMEA2000 unfortunately).

  • Stuart, You may have luck with the Actisense DST-2, which is designed to convert analog sounder transducers into NMEA 0183 that can be used by most any plotter or instrument system:

  • I'm also in the process of doing something similar.

    In the boat, I have two transducers. One through-hull and one in-hull which is of some Airmar p79 variety. Both have C2 or C13 cables and eventually end with an RCA "phono" cable end.

    The Transducer driver head is a still functioning Standard Horizon DS45 which is a 200kHz transciever

    I cross-referenced that depth unit using this and found that it is a 200kHz with a power rating of 650 Watts

    After that I was somewhat satisfied that it might work with the chartplotter unit I'm leaning twoard, the Garmin Echomap 50s. Apparently, it is dual frequency 200kHz and 77kHz which is selectable in the sonar menu. It's not SS or Chirp, so I figure I have that going for me. My thinking is that I would need to keep it on the 200kHz setting.

    Another interesting find was this Garmin makes an 8-pin to terminal wire block that comes with each GSD 24 unit. The part number is 010-11613-00 and it also is mentioned in another Garmin PDF which talks about transducer selection with all the latest sounders. It's listed under the 7x1sx and the new Echomap 50/70s headings.

    The oddity is that a lot of online stores market this adapter as a adpter as only for the GSD 24 but Garmin puts out PDF's that don't agree with that.

    Does anyone have a pinout for the garmin 8-pin sounder plug? Is it the same on all the devices? 7x1, Echomap 50/70s, 5x7 etc etc? My assumption is yes.

    Good luck,

  • Hello,

    I am new to this forum and brand new to boat ownership, a 1987 Catalina 30MKII, though I raced for many years on a 1993 C&C 37R with B&G instruments in my youth.

    The boat I just purchased has a working Raymarine autohelm ST4000 wheel drive and ST60 Tridata display connected to a Magellan Nav 6500 chartplotter. I think it is on a NMEA 0183 network.I would like to update the Chartplotter to a Garmin 741 and and a gWind masthead sensor. Will the Raymarine hull speed sensor and depth information and autohelm work with the new Garmin electronics and vice versa. Sorry if it's a dumb question.


  • Better to ask than make presumptions that lead to disappointment!

    I suspect that what you want is possible but will take some research and possibly a professional. At least of your data networking is happening over SeaTalk but there are ST to NMEA 0183 converters and, better yet, a converter from ST to STng, which is also NMEA 2000.

    You will need to create an N2K network to integrate the gWind with the 741, so I'd be looking at a SeaTalk-to-STng converter and a patch cable to integrate the Ray stuff in. First, though, you should figure out how all the devices are connected now.

  • Ben,

    Thank you for your quick reply. I am going to the boat this afternoon and will check the wiring. I found your helpful article elsewhere in the forum and it looks like what I need.
    I also see another device on Garmin's site which looks what I need for wind input into the system.
    Is the patch cable to change SeaTalk cable fittings to standard or Garmin fittings?
    Thanks again.

  • Rick, The GND 10 bridge box comes with the gWind sensor. Garmin uses standard NMEA 2000 connectors, so to patch a ST-to-STng converter into an N2K network you need this cable with a standard N2K male end:

    But I'm only theorizing about your system and what you're trying to do is somewhat tricky. You'll need to research this carefully and remember that a good installer should be able to figure out what you need after just a short visit to your boat or if you provide accurate diagrams of what's there now.

  • Thanks Ben

    That adapter cable you linked to and the sea talk to ng kit you mentioned in another thread would seem to fit the job in theory. I will ask at the local West Marine dealer if they know of any professional installers when I take them my flow chart.
    Thanks again.


  • hi am new to this site, with a somewhat related transducer problem. have had a 37ft steel yacht for 20 odd years, with the same bronze through-hull transducer.( originally coupled to a Furuno paper sounder). over the years 4 or 5 other digital sounders have been used successfully by just splicing the units to the old transducer. now all the units are more related to finding fish and showing all sorts of wiz-bang bottoms and views. all i require is the depth. A chart plotter would be a bonus, BUT--would i be able to purchase, say a Hummingbird Helix 7DI, and find which are the 200kz wires in the transducer cable and couple these to existing through-hull transducer?. i suspect not, but there has to be a solution. a haulout and new transducer only works until the new head finally dies or becomes unreadable due to weather damage.
    any clues? .regards Don

  • Happy New Year Don,

    Although separate elements are possible, most depth transducers do not have separate elements for 200 Khz and 50 Khz - they use the same element with one set of wires. One of the frequencies is derived through the thickness of the element and the other frequency is derived by reasonating the width of the element. The same caveats apply to using a transducer not specifically designed to be used for the sounder in question.



  • Thanks Bert and Happy NY back,
    Have found a new, but old model, Hummingbird SX 150 which have spliced to old bronze through-hull transducer, and it's working great. So this will suffice until can find further info on using the Helix 7DI,



  • Hi guys,
    Sorry to jump on this thread but all relevant I'm sure. I recently bought a little yacht which has a Garmin GPSmap 551 and Echopilot FLS Bronze with a thru-hull standard transducer. A few weeks later the FLS display faulted and told uneconomical to repair.
    Anyhow, as the 551 is NMEA 2000 I was wondering if anyone knows if the FLS transducer can be adapted or, is NMEA 2000.
    I am looking at this option so as to not make new holes etc.
    Trying to get a cost effective option.

  • Hi Duncan,

    You should contact Echopilot and ask them about the FLS standard Bronze transducer.



  • Bert's advice is good, but note that NMEA 0183 and 2000 "smart" transducers can only transmit numeric depth info, not full FLS or fishfinder data. EchoPilot does make a "Video Engine" that can put the FLS into a common video format that many MFDs can display (tho not a Garmin 551).