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Default Portable Gps/Plotter with AIS-Receiver Support

I don't think that there should be
any "portable" electronics on a boat. In heavy weather they become

missiles
or are lost overboard. I cringe when I hear people talk about laptops that
can be used "anywhere" on the boat. They should be bolted to the chart
table, and by bolted I don't mean kept in place by a piece of shockcord.


Having weathered a few sudden storms I agree. If it's not bolted down and
designed to be used in heavy weather it really has no place being used for
something critical like navigation. Certainly not as the sole provider of
such services. As an add-on for use during fair conditions, sure, laptops,
PDAs and cell phones are great. But I'd never want to depend on using them
when conditions get difficult.

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Default Portable Gps/Plotter with AIS-Receiver Support

"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
--
http://www.youtube.com/watch?v=fEJmc...elated&search=
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Default Portable Gps/Plotter with AIS-Receiver Support

"Meindert Sprang" wrote in
:

What about running an AIS application on a Windows Mobile PDA, inside a
waterproof box, using Bluetooth to receive data from an AIS receiver?

Meindert



I paid Dell for an Axim X51v, their finest Windows Mobile 5 PDA. I
wanted a good PDA to replace my aging Handspring Visor Edge (Palm OS)
that someone gave me a while ago.

Windows Mobile 5 was a disaster! It would lose control of ITSELF, just
sitting there with NOTHING running! The "Today" screen would have WM5's
own programs just disappear for no reason. Dell included a program
called "Switcher" so you could drop down its menu and switch between
running programs that Billy's Boys forgot to put into WM5. Not only
would Switcher's menu simply forget what programs were running because
WM5 lost control of them, if you left it running a few hours, WM5 forgot
where SWITCHER was and lost control of it! Program access from the HOME
screen was similarly crashed. Click on one of WM5's own icons to bring
up the calendar, for instance, and many times it couldn't boot it because
as far as WM5 was concerned IT WASN'T THERE!

The cure was always to start over by flipping the X51v on its face and
using a pin pressing the RESET button to force a hard reboot. This cure
lasted from 20 minutes to 2 hours, when WM5 would, again, crash......

Now, it wasn't my particular X51v. The Dell forums on the subject had
hundreds of users with this same phenomenon, lots of crashing. The Dell
Kiosk in Northwoods Mall still has a crashing X51v on display. Their
cure is to leave the X51v OFF until someone wants to see it run. They
can't just leave it running....like you'd want to run nav or AIS software
on a boat.

Of course, its 3 hour battery life cycle, 30 minutes longer than my
Gateway laptop, is another issue altogether.

I'm back carrying the Visor Edge. It never crashes and you only have to
charge it once a week, even with it running 24/7. Hell, I have two clock
programs running on it that chime every hour and alarm all events and
that doesn't run its tiny battery discharged, either.

Windows Mobile just SUCKS!

Larry
--
http://www.youtube.com/watch?v=fEJmc...elated&search=
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Default Portable Gps/Plotter with AIS-Receiver Support

"Meindert Sprang" wrote in
:

You need to get your facts straight! A Raymarine C/E series

chartplotter
runs at 38400 baud when in AIS mode. Most likely others do that too....

Oh and besides that, there is also something called NMEA0183-HS which

IS
38400 at RS422.

Meindert



hMM....We're buying new equipment, again....sorry. What about wonderful
NMEA2000, or whatever NMEA is calling their latest and greatest version
to sell new equipment this month? Does it run 38,800 baud?

I'm still wondering why we don't just make the AIS receivers run 4800
baud. On a boat with a 12 mile range, there aren't enough AIS ships to
jam a 4800 baud port up, at least that couldn't be buffered cheaply for a
few milliseconds as it spits it out.

Do you know why they insist on 38,800 baud RS-232C, not RS-422 levels??
Seems really stupid to me.

Larry
--
http://www.youtube.com/watch?v=fEJmc...elated&search=
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Default Portable Gps/Plotter with AIS-Receiver Support

"Larry" wrote in message
...
"Meindert Sprang" wrote in
:

You need to get your facts straight! A Raymarine C/E series

chartplotter
runs at 38400 baud when in AIS mode. Most likely others do that too....

Oh and besides that, there is also something called NMEA0183-HS which

IS
38400 at RS422.

Meindert



hMM....We're buying new equipment, again....sorry. What about wonderful
NMEA2000, or whatever NMEA is calling their latest and greatest version
to sell new equipment this month? Does it run 38,800 baud?


No, NMEA2000 is CAN based and runs at 250,000 bps.

I'm still wondering why we don't just make the AIS receivers run 4800
baud. On a boat with a 12 mile range, there aren't enough AIS ships to
jam a 4800 baud port up, at least that couldn't be buffered cheaply for a
few milliseconds as it spits it out.


First of all, the AIS data transmission speed over VHF already 9600 baud so
it would be strange to pack this received data in an NMEA string (more bytes
added) and then squeeze it down a 4800 baud channel.
Further, a moving ship transmits his info at least once every 10s (0-14kn)
to every 2 seconds when between 14-23kn and changing course. So in worst
case your receiver gets one AIS message/2s. Each message contains 168
databits, which are packed into 6 bit charachters for NMEA, that is at least
21 chars of AIS data in a VDM sentence. The minimum VDM sentence length is
then 43 characters. At 4800 baud, this takes up 89ms so at 4800 baud your
AIS receiver would be able to transfer the bare minimum info of 11 ships at
a time. Many AIS messages are however longer and can take up to appr. 1000
bits of info, which would result in at least 3 longer VDM sentences per
ship. Hence the need for 38400.


Do you know why they insist on 38,800 baud RS-232C, not RS-422 levels??
Seems really stupid to me.


Yes and no. One would expect a true NMEA0183-HS interface (38,400 at RS422)
but most, if not all AIS receivers will be connected to either a computer or
a computer based ECDIS. And an simple galvanically isolated intput
consisting of an opto-coupler doesn't really care wether the offered signal
is RS422 or RS232. Between the wires, there is always the same differential
voltage swing of 5-10V in either direction.

Meindert




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Default Portable Gps/Plotter with AIS-Receiver Support

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.


If you think Liverpool, UK is a busy shipping area I suggest you think
again. Think English Channel, Shanghai, Rotterdam, Singapore for
"slightly" busier areas.

Also, range at see that I get is a LOT better than 20 km... The big guys
tend to have their antenna's pretty high up! (My AIS antenna is a Metz
Manta-6 whip mounted 2 m above sea level.)

--
Kees
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Default Portable Gps/Plotter with AIS-Receiver Support

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.


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Default Portable Gps/Plotter with AIS-Receiver Support

I am very happy that many people reply my question which was placed
only in order to remember the manufacturers that there are many users
focused in AIS and needing AIS. I think that the big enterprises are
not very focused on commercial products with AIS, and may consider AIS
a mere fancy for some. I think that Gps/Plotter/Vhf/Ais will be the
future, but it seems that it will be much late than sailors desire.

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Default Portable Gps/Plotter with AIS-Receiver Support

"Meindert Sprang" wrote in
:

Hence the need for 38400.


Actually, the more you think about it the more the "need" is for
Ethernet....for everything.

Stupid old serial nonsense just has to stop at some point...

You can sell them "marinized routers"....(c;

Larry
--
http://www.youtube.com/watch?v=fEJmc...elated&search=
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Default Portable Gps/Plotter with AIS-Receiver Support


"Larry" wrote in message
...
"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
--
http://www.youtube.com/watch?v=fEJmc...elated&search=


Short summary: A 4800 bps NMEA link may very well overflow in
not-insanely-busy conditions. Explanation follows:

A couple of weeks ago I sailed out of Sausalito to see the Queen Mary 2
enter San Francisco Bay. While still in the slip, I saw over 75
simultaneous AIS targets, out to about a 25 NM range. My antenna for the
AIS receiver is just a 6dB (short) whip, mounted on the stern rail, so with
a masthead antenna the range (and number of ships seen) would have been much
greater. I don't know what the burst data-rate was, but let's assume that
on the average each ship is transmitting a "dynamic information"
message-type at 10-second intervals (2 seconds is the fastest update-rate,
12 seconds is the slowest rate for a ship under way)

Ignoring the less-frequent "Static" messages, each message is 256 bits (a
"dynamic" message is 168 bits, plus 88 bits of overhead).

The radio-channel bit-rate is 9600 BPS (from the AIS spec). I don't know
how well the timeslot-assignment method fills the available slots, but the
maximum would be about 375 active ships (256 bits every 10 seconds, times
375 ships = 9600 BPS).

A "dynamic" message gets encapsulated into a 47-character NMEA message.
This is 517 bits (each ASCII character is 8-bits + start-bit + two stop-bits
= 11 bits).

375 active ships, each transmitting one message every 10 seconds would
create an NMEA serial data stream of 37.5 * 517 = 19387.5 BPS. Either this
is a coincidence, or my math is about right. A 19.2 kbps link should be
able to handle full-capacity AIS. It would only take about 93 active ships
to fill a 4800 BPS NMEA link, and this assumes even spacing of the messages,
or very deep buffers.

I can easily see overrunning the capacity of a 4800BPS link, especially if I
had a mast-top antenna. I have a dual-channel receiver, but having one of
the single-channel receivers should cut these data rates in half.

-Paul


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