Larry wrote:
"plano" wrote in
:

If averaged over 10 minutes or so, maybe 4800 would offer enough
bandwidth in certain locations, but you just cannot risk that say 20
(long) AIS sentences are received more or less simultaneously. There
is no way 4800 baud (1/8th!! of 38400) will handle that. Any idea
how much traffic one can expect say in the English Channel? It's the
worst case scenario that counts, not the average in Charleston
harbor. plano



You can watch the Irish Sea:
http://www.aisliverpool.org.uk/index.php
Finest AIS system on the internet.

But, of course, YOUR AIS isn't this good. Your range is about 10-12
miles with a 50' antenna listening to these 12W transmitters. This
limited range limits the number of AIS packets you must process in
your small system. That in itself reduces the load considerably.

Click on [Pan and Zoom] on the Liverpool AIS system. Zoom out until
the scale in the lower left bottom corner says 10 mi - 20 km on your
screen.

Now, pan out of the Liverpool ship channel by the docks. Cruise the
pan out the channel into the Irish Sea, a busy place out from
Liverpool. Go off in the direction of the maximum density of ships
you can find at the time. Using the scale in the lower left hand
corner as a RADIUS from your boat, the actual range of your own AIS
receiver in any at-sea situation, how many ships can you get inside
that 40 km circle around your cursor? In Liverpool harbor, with a
lot of ships docked but still transmitting away on AIS, I can get,
maybe 15 in range. Out at sea, where we are concerned about this
problem, the ships are spread out more. If I center my boat 20 km N
of Amtwch, the peninsula sticking out to the East of Liverpool, at
this moment I would be painting 7 or 8, tops.

Point is your boat-mounted AIS receiver's 20 km horizon ISN'T going to
paint all those ships you can see on this chart of Liverpool and the
Irish Sea, a very busy place for shipping. If 8 ships are
transmitting full AIS data into my system on 4800 baud every other
second, it won't tax the 4800 baud bandwidth anywhere near its limit
to the point where it would jam or nav data packets from the other
instruments would be slowed down to a crawl. It just won't happen,
unless we put up a 1000' mast to get more packets......

Larry

There is another interesting AIS system overseeing the Kiel canal at
http://www.vesseltracker.com/en/kielnok/AreaMap.html

You have to register, which is free to individuals.

See all the convoys and bottlenecks building up, as and when they occur!

Dennis.