NMEA 2000®
Answering some nuts & bolts questions
In talking to dealers and boat
builders around the country,
it’s clear that many have
practical questions about the
installation, application and use
of NMEA 2000®. We asked
Technical Director Steve Spitzer
to respond to several of these.
I’m a CMET with many years of
marine electronics experience. I
Being a CMET certainly provides you with sound technical
expertise in the marine electronics field. Most
Spitzer:
MEJ:
CMETs should have the capability to install
and trouble-shoot products with NMEA
0183. However, NMEA 2000® is not NMEA
0183. NMEA 2000® is a networked system.
Just being a CMET does not mean that you
fully understand the networking of NMEA
2000®. Since becoming the technical director
for NMEA, I have been an advocate for the
marine electronics dealer to understand
NMEA 2000® networking. NMEA has a
course just for NMEA 2000®, which I would
recommend to all CMETs.
We’re supplying very low power to
several tank level gauges. The standard requires that we use a heavier cable than
what’s necessary for the job. Some flexibility
in the requirement would help. Why isn’t that
possible?
Spitzer:
MEJ:
The selection of which NMEA
2000® cable to use is depen-
dant on more than just the power require-
ments for an individual product. The size of
the cable that should be used in an installa-
tion is determined by the total size of the
“nodes” on the network. In addition, the
length of the network should also be strongly
considered when determining the cable size.
The specification tries to assure the safe trans-
port of messages on the “physical layer.”
The selection must be based on the total
power required for all nodes connected to the
network as well as the voltage drop that will
result from the relative location of those prod-
ucts along the network. With careful plan-
ning, as described in an NMEA 2000® semi-
nar, backbone lengths between 5 and 100
meters with the light cable are possible The
cable and connector system, which comes
from the industrial and automation indus-
tries, is designed with tight noise immunity
qualifications, water proofness (submersion
under water) and proper electrical impedance
specification.
Some of the equipment installed
on the backbone doesn’t work as
advertised. Even though it’s supposed to be
NMEA compliant, the product won’t display
the data it’s supposed to. There’s also different
connectors from different manufacturers.
Standardization and seamless compatibility
are big problems. What is NMEA doing to fix
this?
Spitzer:
MEJ:
NMEA and the marine electronics industry have invested
in and embraced the NMEA 2000® product
certification process. Only NMEA 2000®
products that are “NMEA 2000® Certified”
provide a level of assurance that the products
will “behave” properly and “play” with each
other on an NMEA 2000® network. NMEA
does not certify “data.” The type of “data” that
a manufacturer actually populates their
respective product with is the responsibility
of the manufacturer.
The NMEA 2000® data is defined and
standardized for all manufacturers. When a
manufacturer only says that their product
“works with” or is “compliant with” NMEA
2000®, that does not mean they will work on
the NMEA 2000® network properly. In fact,
they may harm the network. All NMEA
2000® products that are certified will interop-
erate properly and are listed on the NMEA
website. The key word here is “Certified.”
The issue with connectors that NMEA is
addressing is that different connectors which
do not meet the standard can adversely affect
the network. Cable and connectors that are
approved for an NMEA 2000® network can
be seen on the NMEA website.
NMEA will strongly defend the investments of all of the manufacturers and customers who have committed the resources to
developing fully certified NMEA 2000®
products. NMEA will continue to police those
manufacturers who may have a negative
impact on the NMEA 2000® network.
