"Bill Kearney" wrote in
:

So I'll go back to my guess that the application layer is the same
but the underlying layers (transport to physical) have been altered
to NMEA 2000.

Incorrect. The bridge cable is passive. The NG cabling, it appears,
just has extra wiring to accomodate the older SeaTalk network. I'm
guessing they did this to allow bringing older SeaTalk gear into the
network without having to run a lot of additional cabling. That is,
bring a line off an older SeaTalk-based transducer and tee it into a
new NG network. Leaves them an opening to attaching existing gear
(sensors, gauges and the like) to the new network. So if you pulled a
new NG 'backbone' network you would be able to connect any older gear
onto the cable without keeping the old network.

It would not have made much economic sense to go with the NMEA2k
protocol stack and not take advantage of the economies of scale
offered by standards-based chipsets.

-Bill Kearney

I'm lost. You say "incorrect" and then state that the cable is passive.
If it's passive, then the my statement is correct. Also, here's the link
to the document describing the SeaTalk protocol:

http://www.thomas-knauf.de/rap/seatalk2.htm

If you look at the datagram definitions, you'll see lots of parameters
which are highly specific to RayMarine equipment and have no mapping to any
NMEA sentances. I've never seen a document describing NMEA 2000, so I
can't comment on that. However, I can't imagine mapping the all of the
SeaTalk datagrams to NMEA 2000 and back. With tons of existing equipment
out there, you need to provide a method of backwards compatibility.

I just looked at the RayMarine ST70 documentation and you can bridge a
SeaTalk network onto a SeaTalkNG network through an ST70 instrument. There
is no way to directly connect a SeaTalk network to a SeaTalkNG network.

Also, you are NOT supposed to bridge a SeaTalk network to a SeaTalkNG
network with NMEA 2000 devices on it. I'm not sure what this implies.

-- Geoff
www.GeoffSchultz.org