Maretron NMEA 2000 Incompatibilities

There is a fundamental incompatibility between Maretron and a number of other manufacturers, including Victron.  With Victron, one prominent place it shows up when trying to display battery data and MPPT charger data on a Maretron display. 

The issue is not limited to battery data - that's just an example - it's really a fundamental incompatibility between how Maretron differentiates the same data (like battery status) for different devices on the network.  The easiest way to explain is probably with an example.

Consider two Victron MPPT chargers.  Each of those chargers sends two different battery status messages;  one for the connected battery, and one for the connected solar panel(s).  Since they use the same N2K message, the two need to somehow be distinguished from each other.  N2K does this using a Data Instance number which is a number in the message indicating which "instance" of data the message is reporting.  The battery status is in Data Instance 0, and the panels are Data Instance 1.  Now anyone on the network listening to the data can tell which is which.  All good so far.

Now consider the second MPPT.  It's sending out the same two messages with Data Instances 0 and 1.  To distinguish these new messages from those sent by the first MPPT, any listening device has to pay attention to which device is sending the data.  The N2K spec is very clear that Data Instances MUST be unique for messages sent from the same device (makes sense).  But it is equally clear that they are NOT required to be unique across devices.  In other words, it's not required that MPPT 1 use Data Instances 0 and 1, and that MPPT 2 use Data Instances 2 and 3.  So Data Instances must be unique within a device, but they are not required to be globally unique across all devices on the network.  The problem is that Maretron DOES require that Data Instances be globally unique across all devices, and that's not possible with some devices, and/or breaks other devices and applications that expect Data Instancing to follow the rules.  This is a short cut for Maretron because all they need to do is look at each message and decide what to do with it based on the Data Instance number.  They don't have to pay attention to which device sent it.  If they were compatible with N2K, they would have to look at BOTH which device sent the message, and what the Data Instance is to decide how to handle the message.  It's more work, and more info to keep track of.

Victron's devices follow the rules, and that makes the messages they send indistinguishable to Maretron.  I currently have 17 different versions of the same battery status message on my N2K bus, 2 each from 4 MPPT chargers, 3 each from 3 different BMS devices, and Maretron can't reliably or controllably display any of them.  There is a way to change the Victron Data Instances to operate in a non-standard way, but doing so breaks Victron's management application which expects devices to follow the rules.

Needless to say, it's very frustrating, with customers left as Monkey in the Middle between two vendors who both say they are operating correctly and that the other guy is wrong, and cite a specification that few if any of us have (I do not), and where you are bound by confidentiality if you do have the specification.  Right now Maretron is incompatible with about half of the N2K devices on my bus, and probably incompatible with 80% of the non-Maretron devices.  This is just one example of why I am continually backing away from N2K, and increasingly treating Maretron as a strictly proprietary system.

 

Voltage Sensing for Balmar MC624 Regulators

When charging batteries, the charge voltage really matters.  Being off by one or two tenths of a volt can result in batteries that never get fully charged, lose capacity, and serve a shorter life.  Most charge controllers have a remote battery sense to address this.  The sense wires carry essentially no current, so experience no voltage drop along their length and can accurately sense the voltage.  You can connect them directly to your batteries, or to your battery bus bar, and get a really accurate reading that isn't impacted by the load or charging current in or out of the batteries and through the main battery cables.

Balmar makes a good voltage regulator for engine alternators, and there are 12V and 24V versions.  The 12V version (MC-612) has a remote voltage sense, but for some reason the 24V version (MC-624) does not.  Instead, it senses the battery voltage through its main power and ground wires.  This creates some interesting challenges in getting a good battery voltage reading.

The diagram below shows a typical regulator installation.  In this example, the batteries are in the laz about 15' away from the main engine and alternator, and the regulator is mounted in close proximity to the alternator.  While underway with electronics running, ventilation fans running, and other power loads, the alternator current can be 100A or more, even as the batteries approach full charge and are not accepting much charge current.  The regulator senses voltage at the alternator, but even with 4/0 cable as shown, there will be a 0.2V or larger drop to the batteries, which is too much for accurate charging.  It really should be a tenth of a volt or less.

Typical regulator installation near engine and alternator

One way to solve this problem is to wire the MC-624's power and ground wires directly to the battery or battery bus bar.  This brings the battery voltage directly to the regulator.  On the surface this would seem like a good solution, but you actually end up with the same problem, just in a different way.

The diagram below shows an installation with the regulator power wired directly to the battery.  But the power wires both sense the voltage and carry the current to power the regulator itself, and more importantly, it's the source of power for the field wire that causes the alternator to product power.  In this example the regulator is drawing 10A, 1A of which powers the regulator, and 9A of which power the field on the alternator.

The power wires need to cover the 15' distance to the batteries, and when you run the calculations to figure out what wire size is required to carry 10A with no ore than 0.1V loss, it's #4 wire which is pretty darn big wire.

But there's another way to solve the problem.  Rather than bring the battery voltage to the regulator, you can instead bring the regulator to the batteries.  Instead of mounting the regulator next to the alternator, mount it right near the batteries or battery bus bar.  That makes the power wires to the regulator very short, yielding excellent voltage sensing with the 12 ga wires supplied with the regulator.  Then make the longer 15' run back to the alternator with the Ignition, Field, and Stator/Tach wires.  Of the three wires, only the Field wire carries much current (9A in our example), and it is relatively insensitive to voltage drop.  Even with a half volt drop in the Field wire, there is no noticeable reduction in alternator output.  I have been using 14 ga, 3 conductor cable and it works great with no loss of alternator output.

Regulator relocated to DC power panel and bus bar

Short wiring distance to DC bus bar

Rose Point Navigation's Nemo Interface

I've been using Rose point Navigation's Nemo interface for 2 years now, initially as an Alpha/Beta test customer, then as a full paying customer.  And I continue to test new releases since I seem to have special skills when it comes to breaking things...

- Nemo is essentially the interface to all your marine electronics. It connects to your marine electronics using the two standard interfaces (NMEA 2000 and NMEA 0183), and connect to your computer via ethernet.

- Because it connects to your computer via ethernet and not USB or serial ports, it actually works reliably. No drivers are required, which is the source of most evil in Windows.

- The NMEA 0183 interfaces are correct RS-422 interfaces, not RS232 which so many people use. The two are NOT the same, and are NOT compatible by design and by specification. Using RS232 to interface to marine electronics is just asking for a flaky, unreliable system.

- It supports four 0183 inputs, so you can bring in data from a number of sensors without requiring external multiplexers. This reduces complexity, reduces the number of failure points, and reduces cost.

- It supports two 0183 outputs. This lets you directly control an autopilot via 0183, and other devices as well.

- In addition to interfacing all your data to Coastal Explorer, Nemo also sends the data on ethernet using a de-facto UDP standard. Other devices on your network can pick up and use this data, like iPad apps, Coastal Explorer running on a laptop, etc.

- It has excellent NMEA 2000 support including superior source data selection. With N2K, all data from all sensors is on the network at the same time. As a result, it's up to each listening device to decide which sensors it wants to use. This is referred to as Source Selection, and some vendors do it a lot better than others. The simplest devices will automatically pick one of each sensor type, and typically they will fail over to another if the first fails. But you have no control over which it picks.

Better devices present you with a list of available devices and let you pick which you want to use. At least this lets you ensure the system is using the best of each device type that you might have. If the selected sensor fails, some will automatically switch to something else, where others require you  make a new choice.

The best devices present you with a list of available sensors and let you prioritize their use, picking which you want to be primary, which is secondary, and so fourth. Coastal Explorer and Nemo do this better than anyone else, allowing you to prioritize any arbitrary number of devices. The only other product I've encountered that comes close it the Furuno NavPilot which let's you prioritize up to three devices for each data type.

- Nemo passes "native" N2K data back and fourth between Coastal Explorer and the N2K network. This means that the actual N2K messages pass through to Coastal Explorer and it processes and interprets them. And Coastal Explorer sends N2K messages which nemo relays to the N2K network. LOTS of other N2K interfaces don't do this, but rather translate between N2K and 0183, communicating with the computer only via 0183. Translation between the two is NOT 1 for 1, and can sometimes be quite messy. Plus you lose all ability to do source selection for your N2K sensors. Nemo does this correctly.

- Nemo can also translate between its 0183 and N2K interfaces. This provides a bridging function between the two that otherwise requires dedicated converter devices. And it does this translation MUCH better than any other device that I've used, allowing you to select individual sentences/PGNs that you want translated, selecting the update frequency, and of course using proper source selection. I have not seen any other device that can do this.  With this translation function, I have eliminated four dedicated converters from my electronics suite.

- Nemo might seem expensive (list price $699), but when you look at what it replaces, it's a real bargain. First, if you are going to add proper RS-422 data interfaces to your PC, it's going to cost you.  Yes, you can get RS-232 USB adapters for about 5 cents each, but remember, they are not compatible with NMEA 0183, and although they will probably appear to work, it will be unreliable. I used one once in a pinch, and all seemed to work OK. But when I looked at the actual sentences being received by Coastal Explorer, a significant portion of them were corrupted. Enough made it through OK for things to mostly work, but do you really want corrupted data running around you navigation system? I sure don't.

Anyway, an ethernet-connected 4 port RS-422 interface can cost $300-$500. So right there is probably 60% of the cost.

Then an N2K interface will cost another $200 or so, and they are all USB connected. That means they only work with the computer they are plugged into, and you have the associated driver nightmares. Nemo gives you the same capability, plus more. The data is on the network, so any Coastal Explorer  (or other) systems can see it. And you are spared the windows driver fiasco. At this point you have pretty much covered the cost of Nemo.

Oh, and because Nemo puts the data on the network, it eliminates the need for one of the many devices that do that as a dedicated function. There's another couple hundred $$ saved.

Then, if you have any data translation conversion required between N2K and 0183, then you really start coming out ahead with Nemo. I have already replaced four $200 converters, and expect to replace two more. That's $800 worth of converters eliminated

- And in good Rose Point fashion, the product is reliable, simple to use, easy to update over the internet, etc.

When you consider what you get for the $$ you spend a dedicated chart plotter, or how much more software like MaxSea costs, and how it solves none of the data interfacing problems, I think Coastal Explorer + Nemo is a real bargain, and one of the best performing products I have used in a long time.

Electric Power Strategy

Since talking about the original design of our power system back when we were specifying the boat, I really haven't said much more about how it's working, what changes we are making, and why.
I've posted this article on our solar system, this article on reworking my main engine alternator system, and this article on the relative efficiency of generating power via the main engine vs a generator.  I have several more articles is process for other modifications, but realize I've never stepped back and provided an overview of what I'm doing, where it's heading, and why.  So here's the big picture.

Solar Panels

As you read through this, think in terms of cruising for extending periods of time, underway some days, but not all, and anchored at night or for several days.  Notably absent are marinas and shore power, so the boat needs to be completely self-sufficient from a power perspective.  Loads need to be powered, and batteries need to be recharged.

If you return to a dock each day and plug into shore power, this is a much easier problem to solve.  All you need is enough power to last until you return to the dock, and shore power can recharge everything.

Similarly, if you run a generator all the time, you will have plenty of power.  As boats get larger, this becomes the norm, and if you are in a climate where you want air conditioning all the time, a constantly running generator is the practical solution.

For other boats, the power we consume comes from an alternator on our engine while underway, from a generator run periodically, or from power stored in a battery bank which of course needs to be recharged periodically.  Increasingly common are solar arrays that generate power as well.  Operating comfortably like this is our goal.   We ran for over a month last summer, never tying up to a dock, and never plugging into shore power.

All of these elements interact in infinite ways depending on how the boat is used, and how it is equipped.  It's important to understand that there is no right answer here, however I always find it interesting to see how other people have solved the problem, and hopefully our approach will prove equally useful to others.

The diagram below shows our power system.  We have ways to generate power; a generator, main engine alternator, and a solar array.   We have a way to store power in the batteries.  And we have things that consume power, some more than others.  It's worth spending a little time on the things that consume power, since they have a large influence on the over-all power system design.

Here's what we have discovered and done so far.


First, we have and continue to pay close attention to our electric loads, and select appliances that are as power efficient as possible without giving up the features we want.  I think we have been pretty successful so far, and have an at-anchor battery load that 1/2 to 1/3 what other boats of the same model report.

Relatively small loads can run off the batteries.  This includes things like lighting, entertainment systems, and various boat systems.  Heavier loads can also run off the batteries just fine as long as they are not prolonged loads.  Our house water pump, microwave, and coffee maker are good examples.  They draw a lot of power, but only for a limited time, so the total power consumption isn't huge.  The greater the cumulative load of everything, the larger batteries you will need and/or the more frequently they will need to be recharged.  Everyone needs to find their happy compromise between convenience of having gadgets, and the inconvenience of powering them.

For heavier, longer lasting loads, running off batteries usually doesn't make sense.  The batteries get drained quickly and need recharging, so it tends to make sense to just run the generator from the onset, powering the load directly, and taking the opportunity to charge the batteries at the same time.

This raises a couple of interesting questions for future articles.  For example, what is the dollar cost of generating power from a generator?  This article compares the fuel efficiency of generating power from a generator vs and engine alternator, but it is comparative only and doesn't quantify the costs in dollars.  And a related question is the cost to store and retrieve power from a battery.  It's not free.  But that can be the subject of another future article.

Batteries eventually need to recharged, and larger loads need to be powered.  We have a solar system, and it contributes nicely, but is limited by the space we have available for solar panels.  On a sunny day it more or less covers our standby loads while at anchor, but there is nothing left over to contribute towards recharging our batteries from the night before.  That still requires some other form of charging, even though the solar makes it less frequent.

That leaves us with two forms of power generation;  alternators on our main engine, and a generator.  Of the two, the generator is the more powerful with a 20kw output.  The main engine alternator is about 5kw.  If we are getting underway, we will typically just let the alternator recharge the batteries.  It can almost always do it before we reach our next destination.  But if we are staying at anchor for the day, we will run the generator and take advantage of the available power to do laundry, heat water, and of course charge the batteries.

But the decision becomes more complex when we are both underway, and when we want to do laundry or run some other larger load like our electric oven or air conditioning.  One option is to run off the alternator and inverters to power these devices.  The other option is to run the generator to power the loads, removing all loads from the alternator.

This brings us to the first enhancement we wanted to make, and the ensuing ripple effect of changes.

While underway, it is a great time to do laundry.  But it required running the generator, yet it's a very light load for the generator.  And our inverter system was 120V only, so we didn't have the option of running off the main engine alternator.  This spawned a project that I will write about in the future where we expanded our inverter system to run a few select 240V appliances - the washer, dryer, and oven to be specific.

Our inverters are capable of powering 7kw which will run two out of three appliances at the same time, and perhaps all three at once.  But our main alternator is only about 5kw, so we needed more alternator output or heavy loads will drain the bateries.  This triggered the first ripple effect and a project to increase our alternator output to about 7kw to match the power of the inverters.

Many people, including me, have increased their alternator and inverter capacity to operate some of these larger loads while underway.  Our initial focus was on being able to do laundry while underway without running the generator.  Laundry by itself isn't enough of a load to keep the generator busy, and not too large a load to power with our existing alternators, so it seemed like a good starting point.   The end result has been quite successful, I think.
One thing I have been wondering through the whole process is how far to take the alternator+inverter approach vs just running the generator.  The next questions I was facing was whether to allow for powering some or all of my air conditioning units via the alternator+inverter.  This question brought about a set of experiments that I ran last summer and reported in this article comparing the fuel efficiency of generating power via alternators vs a generator.  As a result of the experiments, it's unlikely that I will expand my alternator capacity since larger loads are more efficiently powered by the generator.

One related side effect benefit of moving a few 240V appliances to our inverters is that we now have a way to run them while on 50hz shore power.  Our washer, dryer, and oven will only run on 60hz power, or at least that's what the manufacturer says.  I haven't tried it, so am going on what they say.  That created a problem when we get to locations with 50hz shore power.

Our 120V service is 100% serviced through inverters so that always runs at 60hz.  The 240V service, however, was direct connected to either the shore power or generator.  The generator is 60hz, so that would work fine, but not sure power.

By moving the laundry and over to our inverter service, it too now always run at 60hz, so it at least partially solves the 50hz problem.   However, on 50hz shore power our inverters never switch to charge mode and just keep inverting, drawing their power from the batteries.  So there is a need to keep the batteries charged and the inverters fed from shore power.

Back when we first designed our electrical system we considered this and added a universal shore charger.  It's a 100A charger that can run on either 50 or 60hz, and pretty much any input voltage that you throw at it.  So when on 50hz shore power, the charger provides DC that keeps the batteries charged and powers the inverter, and the inverter in turn powers the 120V loads and the 60hz sensitive 240V loads.  It works well, but with the increased inverter load from the laundry, there are times when the charger won't keep up.  So, in the same way we needed to increase alternator output to support the washer and dryer loads, a project for this year is to add a second charger to double its capacity and provide some redundancy when running on shore power.  That will happen sometime before we leave North America.

Hopefully this provides a little more context for some of my more recent projects, and a few articles that I have not yet written.

Engine Alternator or Generator: Which is More Efficient?

This question keeps coming up, and is often debated at length.  Like most endless debates, they go on and on because nobody really knows the answer.  Here's an attempt at getting to a real answer, but I'll spoil it for you - the answer still isn't super clear.....

The question, in a nut shell, is which is more efficient, generating electricity with a big alternator on your main engine, or running a stand alone generator?

One of the first misconceptions is that power from your main engine alternator comes for free because the engine is already running.  Unfortunately that's not true.  Generating that power puts an increased load on the engine which in turn burns more fuel.  It's that old conservation of energy law in physics.  It just won't go away.

Once past that first realization, the debate quickly turns to other power losses, and which power generation source has more losses.  Here's a little score card tabulating the most obvious losses for each generation source.  Once again, there is no clear winner.

	Generator	Alternator
Drive losses	There is virtually no loss in the direct drive between the engine and alternator	Belt drives definitely have friction losses.  How much?  I really have no idea.
Initial form of electricity	AC	AC.  Many people don't realize that your alternator actually generates 3-phase AC.  Inside the alternator it is rectified to DC, with associated losses
Engine efficiency	This will vary with the load.  At light loads, the efficiency is noteably lower	Your main engine will be propelling the boat, so likely operating in a favorable efficiency range.
Powering AC loads	The output is already AC, so no extra losses to power AC loads	The alternators DC output has to go through an Inverter to get AC at about 90% efficiency
Powering DC loads	The generator's AC output needs to go through a battery charger to get DC at about 85% efficiency	The output is already DC, no no extra losses to power DC loads

Of course we all know that running our generator burns fuel too, so the real question is which burns more, the increased load on the main engine, or the generator?  Sitting at the helm while cruising can sometime lead one's mind to wander, and mine always seems to wonder to technical things like this, so one day I decided to measure the fuel burn to generate power from my main engine alternator.  Generator manufacturers publish fuel burn rates, so that data is know.  With corresponding data for generating power from a main engine alternator, perhaps some light could be shed on the question.

To measure the fuel burn required to generate power, I logged my fuel burn for the first few hours after weighing anchor.  The whole time I ran the main engine at a constant setting, then logged the fuel burn as the alternator output went from full output initially, down to just maintaining the underway house loads.  Using the fuel burn rate and power load at the end of the experiment, I was able to tabulate the incremental fuel burn and corresponding power generation from each of the higher output stages.

Here's what the data looks like:

Main Eng burn (gph)	Alt output (A)	Power (KW)	Inc Power (KW)	Inc fuel (gph)	kWh/gal
7.25	258	7.33	4.91	0.55	8.9
7.15	210	5.96	3.55	0.45	7.9
6.90	150	4.26	1.85	0.20	9.2
6.80	115	3.27	0.85	0.10	8.5
6.70	85	2.41

So if you consider the last line as the baseline, each line above it represents some incremental amount of power generated (Inc Power column), and corresponding incremental fuel burn (Inc fuel column).  The fuel efficiency to generate that incremental power can then be calculated as show in the last column.  The resulting numbers jump around a bit, I think because the precision of my fuel burn numbers are limited, but they are clustered together enough to be generally believable, even if not exact.

With this data in hand, it can now be compared to the fuel efficiency of a generator.  My generator is a 20KW Northern lights, and unfortunately they only publish 2 fuel burn data points at 50% and 100% load.  I wanted more than that, so picked the published data from an Onan 21KW unit.

Power (KW)	Fuel Burn (gph)	KWh/gal
21.5	2.2	9.8
16.1	1.5	10.7
10.8	1.1	9.8
5.4	0.8	6.8

At higher power levels, you can see that the generator is more efficient than the alternator, but it's not a huge difference.  And very noteworthy is the significant drop in efficiency at lower power levels where the diesel engine is less efficient.

Plotting all this on a chart helps put it all in perspective.  This chart shows the fuel efficiency of generating power in each device's native form; AC for the generator, and DC for the alternator.

From this you might conclude that for any loads greater than around 35% of the generator's capacity, the generator is the more efficient way to generate power.  That's probably not a bad rule of thumb, but there is still a bit more to the story.

Depending on your generation source, and the type of load you want to power, there might still be another conversion step involved with associated losses.  Let's look at two cases to illustrate this.

First we can look at powering DC loads, including getting your batteries charged up after a night on the hook.  In this case, the power coming out of the alternator requires no further conversion to charge your batteries.  But to charge the batteries from the generator, you need to run the generator's AC power through a battery charger, and they are typically around 85% efficient.  This favors the alternator and handicaps the generator.  The graph below shows the adjusted fuel efficiency of charging batteries from each power source.

You can see that the generator needs to be loaded to around 50% (10KW in this example) of it's rated power to match the efficiency of the main engine alternator when powering DC loads.

The second example is looking at powering AC loads like air conditioning.  In this case, the generator's output is ready to use with no further conversion, but the alternator's power output needs to be run through an inverter at about 90% efficiency.  This favors the generator and handicaps the alternator.  The graph below shows the adjusted fuel efficiencies of powering AC loads.

Now you can see that the generator load only needs to be a bit above 25% to match the alternator efficiency, and quickly becomes a good bit more efficient.

So what's the take-away from all this?  I think two rules of thumb:

1) When powering DC loads, it only makes sense to do so from your generator if you can keep the total generator load up over about 35-40%.  Note that this is the total load on the generator, not just the DC loads.  So if you have your generator on to make water or run your air conditioning and you load is up over 35-40%, then by all means use it for your DC loads as well.   But if you are just plodding along with loads less the 35%, let your alternator do the work.

2) When powering AC loads, the generator pretty quickly becomes the preferred power source, starting at around 25% load, and quickly becoming far more efficient.  For those thinking that giant alternators and inverters might be a good idea to run air conditioning on your boat, think again.  That generator is most likely the more fuel efficient way to power it.  Only modest loads make sense to power from your alternator.

Caveat emptor:

This is just an analysis of one boat and one generator, and not even my own generator.  So please just take this as what it is; just one example and not an exhaustive study.  Maybe I picked a particularly efficient generator, or maybe it's particularly inefficient.  I think it's a representative example, but honestly don't know.  And I have no idea how the efficiency of power generation from my main engine alternators compares to other, but I again expect it's a good representative example.

Auto pilot 2.0 - Furuno NavPilot 700

Almost 18 months ago in this article on my Electronics 2.0 refit, I mentioned that I was moving from a Simrad autopilot system to a Furuno NavPilot 700 series AP.  Here's the brief explanation that I gave:

Dual Furuno NavPilot 700 auto pilots.  Unlike the Simrad pilot, you can actually build up two independent pilots using the Furuno gear so you really have a hot standby.  When I was first evaluating the Simrad gear, I sketched out a dual pilot system and Simrad told me in no uncertain terms, confirmed in writing, that it would work as I expected.  Well, after hours and hours and lots of swapped out equipment, I can tell you with certainty that it DOES NOT work.  Simrad now confirms that it doesn't work, and has never been designed or tested with dual pilots in mind.  Anyway, the Furuno pilots let me finally build the dual system that I wanted from the start.

I've been using it for a while now (probably 3500 miles) and can give a good report on its performance and capabilities, at least in the context of a trawler.

As you can see in the excerpt above, having a redundant auto pilot was an important objective for me.  Actually, our goal has been redundancy for all critical systems, and I certainly consider an AP to be one.  The fatigue level for anyone standing watch is substantially different (like no comparison at all) if you are hand steering vs just monitoring what's going on and watching for logs etc.  From day one the goal was to have two completely independent auto pilots from the control panel all the way through to the steering pump.   That way, if any component fails, you can switch over to the other pilot and keep on going.

I'll save you the drama, but the Simrad pilot can't do that - at least not without a lot of hassle and external switching over from one pilot to the other.  That, plus a hand full of other issues with the
Simrad pilot caused me to switch to the Furuno NavPilot 700.  Doing so was a risk since I had no idea whether I would be making an improvement, or just trading one bag of problem for a different bag.  It turns out to have been a big improvement, but also included a small bag of new problems.

Here's what I like about the NavPilot 700:

1. All the components that make up the NavPilot are NOT interconnected via NMEA 2000 (N2K).  Connecting everything via N2K like Simrad does it is really nice in theory, but given all the issues with N2K, I now favor segregating critical components whenever practical.  The control panels daisy chain together via CAN bus, but it's a closed and dedicated CAN bus used only by a single NavPilot.  The rudder reference sensors are also directly hardwired to the NavPilot computer.  This means more wires running back and forth through the boat, but it also means a more dependable system.  Pulling wires is something you suffer through once, yet dependability you enjoy every time you run the boat.
2. Three different control panels are available, along with at least one wired remote.  This gives lots of flexibility to set things up in a way that works best for you, and that fits your available space.  In my case, I was severely constrained for dash panel space, and the small control panels allowed me to fit two with out a problem.
3. All the control panels have a roto dial control knob.  When the pilot is automatically steering to a particular heading (Auto mode), the dial makes it really easy to adjust the heading in both small and large increments.  I find this much easier than just having buttons to press.
4. The NavPilot computer supports a variety of interfacing options, not just N2K.  This gives flexibility, plus it provides a way  to have an alternate control path from the chart plotter running Coastal Explorer to the NavPilot.  I now have things set up so the pilot will continue to follow my route even if N2K fails completely.
5. The NavPilot has a very good (one of the best I've seen) way to manage source selection for all the external instruments used by the pilot.  For each one (GPS, Heading sensor, etc), you can select up to three different devices, and prioritized the order in which the pilot should use them.  It will then pick the highest priority device, and automatically fail over to the next one on the list if the current device fails.  While I was making adjustments and getting everything to work, I encountered a number of these automatic failovers, and other than an alarm from the pilot alerting you that it changed sources, it just kept on steering like nothing happened.
6. There are no issues with two pilots on the same network, through I do only power one on at a time.  Two on the same network, even powered on at different times, totally messed up the Simrad pilot.
7. The NavPilot has a much better set of tunable steering parameters.  There are three different sets of parameters that you can set up for three different sea states.  With a click and a dial, you can select which set of parameters you want to use.  This has worked out really well and has allowed me to fine tune the steering parameters.
8. And last but not least, the pilot steers the boat very well.  Nordhavns can be hard to steer.  They are very heavy, move relatively slow, and have big stabilizers.  Throw in some sloppy seas, and the pilot works hard.  I was always happy with how the Simrad pilot steered the boat, but I can say that the Furuno pilot is at least as good.  Throw in the selectable parameter groups, and I'd give it a nudge above.

Controls for dual pilots (inactive one covered), and programmable groups of steering parameters

Several different control panels, all with roto-dial controls

That's a lot to like, and as a result I've been very happy with the NavPilot.  However, it's not without its shortcomings.

But, as background for discussing one of the shortcomings, it's worth talking about follow-up steering controls.  Smaller boats don't use these, but bigger boats do.  They are lever controls that essentially give you power steering, and very fast power steering at that.  There are two flavors; Follow-up, and Non-Follow-up.

A Follow-up (FU) lever is the easiest to understand.  It's a lever or knob that is used to position the rudder.  Center the lever and the rudder centers.  Turn to 15 deg port and the rudder goes to 15 deg port.  Turn hard to stbd and the rudder goes hard to stbd.  It's a bit like a tiller on a small boat and, to its name, the rudder "follows" the Follow-up lever's position.  These are indispensable for maneuvering larger boats where manually turning a wheel just isn't fast enough.  Our wheel, for example, is 10 turns hard over to hard over, and it's not a one hand operation.

Follow-up (FU) steering control

A non-follow-up (NFU) control is a little different, and has three distinct control position.  Centered, there is no rudder movement.  The rudder stays in whatever position it's in.  Hold the lever to the right and the rudder moves to the right.  As long as the lever is held to the right (it spring-loaded and will pop back to center if you let go) the rudder will keep moving to the right until it hits its stop.  Hold the lever to the left, and the rudder starts moving to the left.  So rather than commanding a rudder position as you do with a FU control, you are commanding rudder movement with a NFU control.

Non-Follow-up (NFU) steering control

With that background, here's the list of shortcoming in the NavPilot 700:

1. Very limited support for Follow-up and Non-Follow-up control levers.  Furuno only makes one very simple follow-up (FU), and resells a couple of FU and NFU levers from other vendors.  But the bigger problem is that the NavPilot only supports a maximum of two FU controls, and even then it doesn't do well.  On our boat we need a minimum of 3 FU controls; one each in the pilot house, port wing station, and stbd wing station.  And there is an argument for one on the fly bridge and another in the stern station.  And even with two, operation is highly problematic.  Each FU control has an on/of switch.  When you switch one on, the pilot enters FU mode and you can steer from the FU control.  That's fine.  But if you turn the other FU control on at the same time, it operates both of them in parallel.  Electrically the control is very simple and consists of nothing more than a potentiometer which is just a variable resistor controlled by a dial.  When you connect two of them together, you get very unexpected steering results and the rudder veers off in an unexpected way.  The only way the boat steers correctly is if you make sure you only enable one FU control at a time - something that my feeble mind has trouble doing.  I'll be steering from the pilot house, then step out to the wing station to make a final approach and dock.  If you forget to turn off the pilot house control and turn on the wing control, the steering goes haywire.  Not good when docking.  This is something that Simrad does much better than Furuno.  With Simrad, you can have an arbitrary number of FU controls, and each has a "take command" button.  When you take command from one station, it automatically disables any other station.  It works much, much better.  This is an area where Furuno really needs to do some work, and it makes it very hard for me to recommend the NavPilot for boats that need more than one or two FU controls.  However, I have come up with a solution that completely solves the problem, though it requires a lot more work to build than I expect most people will be willing to do.  I'll cover this in another article later on.
2. Surprise, surprise, the NavPilot has some N2K problems.  For some inexplicable reason, it sends out repeated requests to all devices asking for the Humidity PGN.  These requests go out about every 7 seconds and all devices have to stop and respond in one way or another.  It's mostly benign, but totally brain dead and creates a bunch of unnecessary traffic and potential disruption to other important traffic.  I've reported this to Furuno but they have brushed it off and don't appear to have any plans to fix it.

Fortunately, I've been able to work around both these issues and have a pilot that I'm very happy with.

It's probably worth a few minutes to talk some more about the dual auto pilots since that was such an important consideration.  I mentioned earlier that I only run one at a time.  More specifically, each is on a separate power breaker and I have an interlock that ensures only one is powered on at any time.  I'm actually pretty sure that this is NOT necessary, and that I could leave both powered on at the same time as long as I made sure not to activate them both, i.e. I'd always have to be sure at least one is in Standby mode.  But that's subject to operator error, so I prefer the breaker interlock.  The only down side is that if one pilot fails, I need to power up the second before it can be made active.  But that only takes about 30 seconds, so is really not a problem.

Dual Accusteer continuous duty steering pumps

To ensure everything works, I alternate between the two pilots about once a week.  So I'll run on one for a week, then switch to the other for a week, then switch back.  In the pilot house there are two control panels, one for each pilot.  I leave the cover on the pilot that's not in use so it's easy for the operator to know which one is active.  On the fly bridge there is only one control panel connected to pilot #1.  I figure if we are operating from the fly, we can just use that pilot.