Tender NMEA2000 System

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Frequent readers of this blog know we like NMEA2000 and have become very dependent upon Maretron N2KView at the core of our monitoring and control system on Dirona. The screens above are our underway and at rest monitoring displays for Dirona. They are repeated in the pilot house, salon, and master stateroom.

Knowing how much we use NMEA2000, it’s probably not a big surprise that we went with NMEA2000 in our new AB Oceanus 12VST tender but it actually took us a while to get to that decision. Since we selected a Honda 50 outboard, we started with considering the gauge packages available from Honda. The least expensive are analog gauges like we had in the previous tender. The higher-end options are no less expensive than NMEA 2000, but less flexible and less open. I still hadn’t really considered NMEA2000 until we noticed the Honda 50 produces a vast quantity of NMEA 2000 data including: RPM, engine temperature, trim level, fuel consumption rate, engine hours, and start battery voltage with lots of others. It would be really useful to have access to that data and I’m fairly comfortable with NMEA 2000 work at this point, so doing the tender in NMEA2000 wouldn’t be much work.

Going with NMEA2000 opens up some other interesting options. On Dirona, we implemented a database that records all data from the entire boat every 5 seconds and we have that data going back to 2012. Clearly I’m not going to deploy a PC running MariaDB in the tender but, since we implemented our custom recording system, Maretron has introduced a commercial product in a small box that does much the same thing. I really liked the idea of being able to run tender reports to show the route we have traveled, depth and other conditions along the route, or engine state. Another reason to try NMEA2000 in the tender is I wanted to try the Maretron VDR100 vessel data recorder. Later on I’ll show some screen shots from the VDR100 output.

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Maretron N2KBuilder

Having decided to do a NMEA2000 system, I thought I would also give the Maretron N2KBuilder program a try since all these products were not available when we originally designed the NMEA 2000 system we have deployed in Dirona. N2KBuilder is excellent in that it is easy to use, free, documents your final NMEA2000 design, and most importantly, it checks your design for NMEA2000 compliance preventing you from making design choices that will lead to an unreliable or inoperative N2ksystem. You won’t forget a terminator resistor or accidentally have excessively long drop connections. Once N2KBuilder approves a system, its super simple to just screw the parts together. This is the design we selected for the new tender.

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In the design above, the only difference is, for a depth sounder, I went with an Airmar P75 depth sounder rather than the Maretron DST110 shown. Either would work fine and both are fully supported by the Maretron control and monitoring systems, but the P75 has the advantage of working with higher dead-rise angles and it’s a shoot-through-the-hull design that is easier to install.

The system is now fully installed except for the fuel sensor, and has been running well for the last two months and about 30 hours of tender use. I’m confident the fuel sensor will also work well and am in a rush to see it installed. But the existing fuel gauge fitting is a screw-in design that brings 2 issues: 1) I don’t have the adapter to fit the Maretron TLM150 tank level monitor to this tank’s connection, and 2) the analog sensor was screwed in so tightly at the AB factory that I’ve not been able to get it out.  I really need to do something on this because fuel level is a pretty important data point and the existing sensor reads empty at about 2/3 of a tank (more than 5 gallons), so is close to useless. We’re currently north of the Arctic Circle in Norway so it’s cold out there. When we have warmer weather, I’ll find a way to get that analog tank sensor removed from the tank so I can install the TLM150 NMEA2000 sensor.

Maretron DSM410

The heart of the tender NMEA 2000 system is the new Maretron DSM410 display. It’s a super bright display that is easy to read in direct sunlight and can be dimmed down for night operation with a single keystroke. The DSM410 is beautiful and, like all DSMs, can display vast amounts of data on up to 16 customized screens.

On Dirona we use two DSM250s and two DSM150s (since replaced in the Maretron product line by the DSM410) and really like the DSMs. Not only can they display any data we have on either the tender or on Dirona but they can also alarm. So, if you are tired of bending props, you can set an alarm on low depth. Or you can alarm on high engine temperature or any other parameters.  To get a perspective on what can be displayed and how easy it is to use, here are the screen configurations we use on the tender DSM410:

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Underway Data

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Engine Data

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Fuel Data

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Location Data

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Locale Information

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Vessel Data Recorder State


Maretron GPS200

Adding a GPS to this package requires finding a near flat location for the Maretron GPS200 GPS and then it just screws into a tee in the network. I didn’t change or configure anything and, once it’s installed, you have speed, heading, location, and other GPS related data.

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Click image for a larger view

Airmar P79

We initially planned to go with a Maretron DST110 as a depth sounder, but the AB tender has more than 20 degrees of hull dead rise. The large dead rise angle helps make the boat remarkably stable in rough water, but it does slow it somewhat and makes the depth sounder installation somewhat more difficult. The DST110 is not recommended for high dead rise angle installations unless a fairing block is used to give it a direct straight-down shot. I didn’t want to put a large appendage on the outside of the hull, so ended up going with the Airmar P79. It has the advantage of being a shoot-through-the-hull design so it’s not necessary to drill through the tender bottom. And this particular sensor has an adjustment block to eliminate the dead rise problem. The P79 can only deal with up to a 20-degree hull dead rise and we are slightly more, but the sensor is close enough to vertical to work great. Another advantage of this sensor is the Maretron DSM410 (or any other Maretron DSM) recognizes it and is able to configure the depth sounder as needed.

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Airmar makes something close to 100 different depth sounder variants and nearly 10 different variants of the P79. It turns out, if you buy a depth sounder from Furuno, Maretron, Raymarine, Garmin, etc., you are almost certainly buying an Airmar part.  In our case we went with the Garmin variant of the Airmar P79: Garmin Depth, P79 in-hull, N2k Smartsensor.


Maretron VDR100

Our use of the Maretron VDR100 was a bit of an experiment. When we built the NMEA2000 system on Dirona, Maretron didn’t have a vessel data recorder so we built our own using a relational database. It’s a great system, but was a lot of work to get running and when people ask me what we recommend, it not a great answer to say “go hand-craft a relational database with all custom reporting”. We wanted to try the VDR100 to see if it’s a good solution to track parameters changing over time and to support plotting the vessel’s route on Google Maps.

We have had the VDR100 in use for about four weeks now so we are starting to get a view for what it can do in combination with the N2KExtractor software. This display is the most useful where it plots over Google Maps the boat’s route between any two points in time:

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Tender Trip in Google Maps

It can also graph most NMEA parameters. As an example, the graph below shows engine RPM (blue), engine trim angle (green), and speed (red). Here you can see the speed increase as the engine is trimmed up and you can see the tender can do 37 mph (32 kts) with two people on board. From this graph you also can see that the engine is able to get the boat up on plane easily and max speed is at 5800 RPM, which means we have exactly the right prop (Honda specifies 5,500 to 6,000 RPM at wide open throttle). The graph gives a good clear view of the tender performance and how hard the Honda needs to work for a given boat speed.

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Engine RPM, Engine Trim Angle, and Boat Speed

Another example is the graph below showing engine temperature (blue) and engine RPM (green). Here you can see the engine temperature continue to increase during long runs. In fact, on this trip, it was never running flat out long enough for the temperature to stabilize. From other trips, we can see that when running at maximum output for long periods of time the engine temperature stabilizes at a fairly high 225F.

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Engine RPM and Temperature

The VDR100 saves all data and produces interesting graphs. The VDR100 and N2KExtractor software combination could be a bit easier to use and have some rough edges that need to be worked around, but there is no question that the reports are interesting. The boat track plot over Google Maps is particularly useful.

Maretron DSM410

Just as the Maretron N2kView system is the heart of the monitoring system on Dirona, the Maretron DSM410 display is the heart of the system on the tender. I was originally going to mount it flat in-dash but Jennifer correctly pointed out that we would have to lean forward to read the depth.  So, I decided to fabricate a display that we can see easily from any seating position and both the passenger and operator can easily see it.

I fabricated the mounts out of a sheet of marine board and an old plastic radio mount. Here’s the beginning of the fabrication process:

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And this is the finished DSM410 mount:

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The final installation:

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Analog Gauges

As part of this installation we decided we would keep the Honda analog gauge package as a redundant source of data.  However, the gauges where mounted at perhaps the worst place I have ever seen when the boat was delivered.

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Yes, those gauges really were at our knees and aimed downward :-). We moved the gauges up to the top of the dash where we can easily see them (pictured above with the DSM410) and installed a blanking panel to cover the old holes. We don’t intend to use these as anything other than backup but they still need to be visible.

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If you have an outboard motor that produces NMEA2000, you should give serious consideration to building a Maretron system for the boat. It gives easy-to-read display of all parameters, supports alerting and alarming, and allows all data to be collected for later display showing the route you covered and, if you want, you can drill into any parameter like RPM, speed, engine temperature, and trim angle. It’s a very flexible but easy to use system and it’s useful to have the data. The DSM410 is an incredible display both easy to read in bright sunlight and easy to configure, also supporting alerting and alarming.

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14 comments on “Tender NMEA2000 System
  1. Tim Daleo says:

    Is the new tank gauge giving you accurate results? Did you have to calibrate it or was it ok for the tank style?

    • It’s installed but it’ll need to be calibrated. The way these sensors work is they can tell you the distance the fuel is below the sensor as soon as they are installed but you want them to tell you the amount of fuel. To do that, the tank needs to be emptied and then filled in up to 16 increments where, at each stop, the amount of fuel is programmed into the device. After that, the system will accurately show fuel level.

      The TLM150 will be accurate. The concern is the tank is low and flat and the boat sits at a slight angle. The tank sensor is at the tank middle so it’ll give a reading there that should be quite accurate but the angle of the tank may hide quite a bit of fuel down slope from the sensor reading empty at the middle of the tank. I’ll learn more once we empty the tank and calibrate it. The calibration is easy — what takes time is emptying the tank. It currently has about 8 gallons in it so I’ll need to siphon it off or just wait until I run it down.

  2. Timothy Daleo says:

    I enjoyed reading about the new tender and NMEA network. I would like to see how you wired and routed everything inside the console.

    I have a small Inmar tender with a Honda 20 (no NMEA, carb) so I used a NoLand Engineering RS11 data converter to get basic data from the engine. I connected a Garmin 820XS, transducer, Garmin fuel sensor, Fusion stereo and Lowrance VHF radio all to the NMEA network. I have not added a way to record data yet but I do run a Yacht Devices voyage recorder ($189) on the Sea Ray and might consider buying another one for the tender someday. As a note, the recorder has an SD card and then I import into a pivot table that I made that uses formulas to combine engine and speed data so I can look back on performance, engine load, mileage and detailed track data.

    I hope you get back to the West Coast someday. I would really like to meet you both, buy you a beer and learn how the pros navigate the world.

  3. Jostein Lima says:

    Hello James!

    I just wondered if you considered using a chart plotter as display instead or perhaps even in addition to the DSM 410?

    Taking the opportunity to thank you for all your great articles. It’s a really valuable source of information.

    Glad you enjoy Norway, my home country. Southern parts Kristansand/Arendal/Kragerø are also nice for boating:-)



    • That’s a good question — we would like to have a chart plotter on the tender. The core problem is chart data. For a chart plotter to be of any value at all, you need to have charts. When a tender is used throughout the world, you need to have chart data for the entire planet and that would end up costing about half again the price of the tender. That’s just not practical so we have a reliable and easy to read depth sounder on the tender and print out charts from Dirona when heading out on longer tender trips.

      • Jacques Vuye says:

        That’s an interesting question indeed!
        I have a similar issue with my multi purpose display on my e-mountainbike (Yes James, the same one you helped me set up with the right parameters when I programmed it 3 years ago)
        The problem here too is that for the GPS part of thsi display (Bosch Nyon) the maps are accessible when connected to the mobile network (using your smartphone) . But when you’re mountain biking you often end up in places where there is no mobile data service!
        However I found a source from which I can selectively upload map tiles of the area I’m planning to explore.
        Is there a similar source of Marine charts that allow selective tiles upload ?
        Or could you upload tiles directly from the marine charts you use on on Dirona?

        • The charts on Dirona are protected by the chart provider with digital rights management to prevent them from being used on other than licensed devices. Furuno does allow us to install them twice so we can have two redundant copies where one is accessible via the nav computer and the other is accessible via the Furuno black box. They can’t be used on the tender though. We often print charts on Dirona and use them on the tender which isn’t bad.

          Another nice approach is to install Navionics on a mobile device. They have good quality charts sufficiently inexpensive that Jennifer usually has a set of charts on her phone as well which would be with us in the tender.

          Some cruisers download Google Earth and convert them to a format readable by their chart systems.

          • Sam Landsman says:

            I use a smartphone with Navionics charts as a plotter in the dinghy. Add a RAM mount and waterproof case and it works well. Charts are pretty cheap. The biggest problem is battery life, but in decent weather that can be solved by plugging in an extra battery.

  4. Steve Davis says:

    James, Have you ever given any thought as to what could happen when you’re drilling about 5 inches from the “family jewels”? Might give this some thought next time, and maybe use a work bench.

    • It’s one of the many small boat challenges — space is at a premium when the boat is where you live all year around. When we had a home I had a Black and Decker foldable workbench that I found really useful. On the boat, I don’t have a good place to store it so I end up working without it.

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