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NMEA transducer (depth sounder)

A transducer is the hardware piece which goes on the bottom of your boat. They can measure things like depth, speed through water, temperature, etc. Can you be on the water without one? Absolutely. However, it’s a good idea to have a transducer in addition to marine charts and GPS. This gives you another crucial piece of information, and an additional layer of safety. NMEA transducer is a unit which conforms to the NMEA 0183 or NMEA 2000 specifications. This makes them somewhat universal and interoperable with various brands and equipment. Yes, this means you can connect an NMEA transducer to one of my navigation laptops or tablets.

NMEA 0183 vs NMEA 2000 what’s the difference

Most people already have existing equipment on their boat that they are trying to connect to one of my systems. However, what should you choose if you need to install a transducer from scratch, for example? NMEA 0183 is a simple serial connection. You can connect the transducer to one device. NMEA 2000 is a network technology and can share the data to many devices seamlessly. NMEA 0183 is older, and hence you may be able to find used parts cheaper. If you’re looking to get the data to multiple devices across your boat, NMEA 2000 would be the choice for that. Otherwise, NMEA 0183 should be cheaper and simpler to integrate.

Note: simply connecting a transducer to a computer won’t give you a fish finding picture automatically, just text data of things like depth, speed, water temp if the transducer collects them. For more info on having a fish finding picture, take a look here.

NMEA transducer and installation types

Airmar made this very helpful summary slide. Since I’m advertising their NMEA transducers below for free, I’m borrowing it 🙂 Transom mount (no hole needed) and thru-hull (you’re drilling a hole) types are the most common. In-hull (works without a hole through the hull) can be a nice option but they aren’t always very accurate, or so I’ve heard.

NMEA transducer types

What data can an NMEA transducer measure?

This is individual to a given model, so read the spec sheet. However, here are some capabilities.

  1. Depth. This is self-explanatory, and the main reason people want to have a transducer. Keep in mind that different frequencies work for different depths. Make sure the depth range that a given model can sense is suitable for your application. Generally, people who cruise care about getting in close to shore but staying off the rocks.
  2. Speed. All of my navigation systems can show you speed over ground (SOG) from the GPS signal. The transducer can measure actual speed through water. This is useful in some situation, for example going with or against a current.
  3. Temperature. Keep in mind that water temperature can change wildly between different depths, and this just samples it at one depth.
  4. Attitude. Basically this shows the angular deviation from the axes, i.e. how much your boat is listing to one side vs the other.
  5. Fish finding – a colored picture of what’s actually under your boat also uses a transducer. However, it’s actually a combination of software and hardware. None of the below units will do that on their own!

Below are some NMEA transducers. This is not a comprehensive listб just some models you can consider for your boat.


NMEA 0183 Transducer – actual models you can buy

Airmar NMEA Transducer. In-Hull: P79s. Thru-hull: DST800, DT800 or B122, UST800. Transom: P39. Make sure you pick the NMEA 0183 version as they are also available as NMEA 2000. Also made by AirMar, but branded Furuno. Thru-hull: B17, P17. Transom: P66.

CruzPro NMEA Transducer DSP Active Depth can be found here, along with some helpful diagrams. The models include the following. Transom: ATT120A, ATT120B, ATT120AT, ATT120BT. Thru-hull: ATU120A, ATU120B, ATU120AT, ATU120BT, ATB120A, ATB120B, ATB120AT, ATB120BT. 


NMEA 2000 Transducer – actual models you can buy

Airmar NMEA Transducer. In-Hull: P79s. Thru-hull: DST110, DST800, DT800 or B122, UST800, DST810. Transom: P39. Make sure you pick the NMEA 2000 version as they are also available as NMEA 0183.


Transform your old analog transducer into NMEA 0183

Actisense makes DST-2, which is an adapter that digitizes analog depth, speed & temperature data. In other words, you plug your old analog transducer into it and it gives an NMEA 0183 signal. At about $300 USD, it’s not that cheap though.


This is by no means comprehensive information, but I hope that you’ve found it useful. If you’ve got any questions about my systems or got any questions for me, please contact me.

Connecting an NMEA transducer to one of my navigation laptops or tablets

Any NMEA 1083 or NMEA 2000 transducer can be connected to one of my units. The 10, 13, and 15 inch navigation laptops are the easiest to integrate with NMEA 0183 since they have a native RS-232 (DB-9) nine pin serial port. I carry the break out RS-422 / RS-485 adapter for that, just ask when you order. Keep in mind that OpenCPN and some other navigation software is compatible with NMEA 0183 but not NMEA 2000. Some of the adapters can translate on the fly! Below are some pin outs for various NMEA 0183 plugs. Data out on the transducer side should be connected to to data in on the computer side, and vice versa. The baud rate is 4800, and the serial port usually is COM1. Note that you’ll need to chop off one end of the NMEA 0183 cable and wire the data in on the device to data out on the adapter, and vice versa.

 

NMEA 2000 or NMEA 0183 on a tablet requires a wireless multiplexer or a wired adapter. Here, I have a page discussing various available options for that.

Why use a navigation laptop as a chart plotter?

My navigation laptop systems can be much more affordable than Garmin, Lowrance, Simrad, B&G, Furuno, Humminbird, Raymarine, Si-Tex. I will also support my units forever! Furthermore, I believe that some of the commercial chart plotter brands gouge their customers. Large companies force their clients to upgrade by no longer supporting older units with chart and software updates. In addition, they charge outrageous fees for simple things like a larger screen size. I don’t do any of these things, and never will – guaranteed! In addition to these, please take a look at other advantages as well.

I am always happy to answer questions, and provide additional information. For example, exact dimensions, video demos of how something works, precise capabilities, screenshots of charts in your area, and more. I configure each unit specifically for you, which takes considerable effort. Therefore, please note that non-defective returns are only accepted within 7 days of receiving the unit and are subject to a 20% restocking fee. Some examples would be: change of mind, didn’t fit the available space, missing functionality, etc. I would much rather answer your questions before you order so I can confirm it can do what you need. I have a lot of experience, so this is not a problem! If you’re not sure if the system can do what you need, just ask me or please take a look at the video demos.

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