Some History:
I recently purchased a "new" used 32' sailboat. I am currently
working on gutting the existing "rats nest" electrical system. In
addition to the electrical system, I am also going to replace the
instruments onboard. The previous owners have installed a Heathkit
speed/log, and a Standard Horizon depth sounder, both are in need of
replacement.

My dilemma is the last year I purchased a Lowrance LMS-337C
(http://www.lowrance.com/marine/Products/LMS-337CDF.asp) for my
previous boat. This worked out very well for that boat because I was
only interested in GPS, depth, and chart plotter. On my new project I
work like to also include an anemometer during this electrical
overhaul. I would also like to be able to add an autopilot and radar
in the future (perhaps later this season). Unfortunately, Lowarnce
doesn't have anemometers or autopilots and I think this unit only
supports NEMA 2000. I have found that Maretron
(http://www.maretron.com/) seems to offer a full product line of NEMA
2000 sensors including ultrasonic anemometers and additional LCD
displays. Lowrance does offer radar on their larger displays, but not
for the one I currently have, so to add radar I would need to buy a new
display anyway, however I would be able to install the 337C in the
cabin at the Nav station as a backup and do route planning out of the
elements.


My questions:
What would be the most practical solution for me? Does the NEMA 2000
standard work as well as advertised for multi-brand systems? Should I
sell my Lowrance unit and go for a one-brand boat such as Raymarine,
Navman, or Comnav? If I start over from scratch for my primary cockpit
unit, is there any merit in mounting the Lowarnce down below?

What would be the most practical solution for me? Does the NEMA 2000
standard work as well as advertised for multi-brand systems? Should I
sell my Lowrance unit and go for a one-brand boat such as Raymarine,
Navman, or Comnav? If I start over from scratch for my primary cockpit
unit, is there any merit in mounting the Lowarnce down below?

NMEA2k does indeed interoperate pretty well. I've got Lowrance fuel flow
senders talking to my Raymarine E-80 chartplotter. I've also got a Lowrance
GPS feeding the E-80.

The only downside to NMEA2k at this point is configuration. It appears you
need to have a display from the same vendor as the sensors in order to get
them configured (or updated). I added a Lowrance LMF-200 display just for
this purpose, but also found it useful to have the fuel data on a separate
gauge anyway. But if I wanted to add the Maretron fuel tank level senders
I'd need to either get a Maretron display or their USB gateway and use a PC.
The config and updating is a one time thing so I'd probably go the PC USB
route.

Most systems these days support both their own networks and NMEA2k. It
appears that using the vendor systems for autopilot and such is the only
solution (today). So perhaps you'd want to start from the needs best served
by the vendor network types and build-out from there. You want the
autopilot or other things you NEED working first and worry about adding on
other stuff once that's sorted.

-Bill Kearney

Bill,

Thanks for the feedback. Yes, at this point I'm just trying to get the
basic instruments working and functional. I just want to make sure
before I spend more money that I am not painting myself into a corner.


I am fairly comfortable with NMEA-0183. A few years ago I designed an
FPGA device to convert the data from my handheld Lowrance GlobalMap100
to a standard VGA display to make it larger and easier to see. Another
project involved reading in the position from multiple (3 or more) GPS
units over the 0183 bus and my microcontroller decided if any of the
GPS's on the network were malfunctioning, and if so it would alert me.


I suppose my lack of NMEA-2000 protocol knowledge that makes me worried
about investing money into these instruments. I have read as much as
possible without purchasing the actual standard, and it sounds like
everything should dovetail nicely, on paper at least . The
proprietary standards out there frighten me much more. I hate the
thought of sitting down with a logic analyzer trying to decode those
proprietary standards if I ever want to add my own custom hardware the
network again.

Thanks,
Mike

I hate the
thought of sitting down with a logic analyzer trying to decode those
proprietary standards if I ever want to add my own custom hardware the
network again.

Eh, when I'm on the boat I have little desire to hack it. I want it to
operate and not leave me and my passengers in a bad situation. Thus I'm
prepared to live with the way various vendors have chosen to network their
devices. I've got NMEA2k running between my two engines, doing RPM syncing
and transmission control. I "could" bridge that network to my other NMEA2K
network and get at the data. But I'd rather not put something as crucial as
that at any sort of additional risk. I'd feel the same way about anything
actually in control of navigational gear.

I suppose it's both fortunate and unfortunate that they've made the NMEA2k
standard inaccessible. Fortunate that it may serve to keep some junk off
the network (although just because a company could afford the spec doesn't
guarantee...). And unfortunate because it may stifle a bit of low-end
tinkering. But as long as the gear it networks operates reliably, and my
estate can sue the companies if it doesn't, well, that's ok by me.

So I guess I'm suggesting that you give serious consideration to separating
your networks. If you want to tinker then put those devices on their own
network. Put the crucial stuff on it's own network. At least with NMEA2k
(or seatalk for that matter) you've only got a single cable to run.

I'll say this, however, it's my intention before putting it back into the
water to re-rig how the networking runs in our boat. I've had a few
situations where GPS inexplicably went out. No amount of debugging (and
I've really tried) pointed a finger at the culprit. I've gone with adding a
second GPS on a different network (NMEA2k aka SeaTalk2). The boat shipped
with GPS on the SeaTalk network into the chartplotter. But the cabling ran
such that it's not conveniently accessible to allow shunting off
questionably performing devices. So I'll re-route a few of the cables to
let me do it. I'd prefer not to have to do it but it seems like having the
option is the smart thing to do.

You might want to keep that in mind when you're looking at how to route your
cables. Since everything's on a single bus it does help to be able to get
something off the bus in the event it's causing trouble. NMEA2k makes this
easier by using T-connectors. You can simply unscrew a device from the Tee
and the network won't care. Just make sure you've got decent access to all
the Tee connectors and some extra cable to make direct connections should
problems arise.

I've had a sneaking suspicion that the cause of my woes is low voltage. But
when things act up level's still reading a good 12v. But I haven't gone so
far as to add some sort of strip-chart or logging process on a PC to be sure
of it. The problem's so random and infrequent that it hasn't been worth
that much hassle.

-Bill Kearney

Bill Kearney wrote:
I hate the
thought of sitting down with a logic analyzer trying to decode those
proprietary standards if I ever want to add my own custom hardware the
network again.



I'll say this, however, it's my intention before putting it back into the
water to re-rig how the networking runs in our boat. I've had a few
situations where GPS inexplicably went out. No amount of debugging (and
I've really tried) pointed a finger at the culprit. I've gone with adding a
second GPS on a different network (NMEA2k aka SeaTalk2). The boat shipped
with GPS on the SeaTalk network into the chartplotter. But the cabling ran
such that it's not conveniently accessible to allow shunting off
questionably performing devices. So I'll re-route a few of the cables to
let me do it. I'd prefer not to have to do it but it seems like having the
option is the smart thing to do.



-Bill Kearney

Those familiar with my wifi odyssey know that I'm barely dangerous, let
alone knowledgeable about networking.

However, I recently was able to integrate SeaTalk and NMEA devices
through the computer section of my (older) ST6000 autopilot controller.
The controller could take either input, and output in the language
going to the particular device.

Perhaps something of that nature would work here?

Meanwhile, I'm dumping the stuff I started with and trying something
different for the wifi. What I have clearly isn't how I like, though,
as this post demonstrates, *does* allow me intermittent connectivity.
L8R

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