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#21
posted to rec.boats.electronics
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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. |
#22
posted to rec.boats.electronics
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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= |
#23
posted to rec.boats.electronics
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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= |
#24
posted to rec.boats.electronics
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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= |
#25
posted to rec.boats.electronics
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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 |
#26
posted to rec.boats.electronics
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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 |
#27
posted to rec.boats.electronics
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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. |
#28
posted to rec.boats.electronics
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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. |
#29
posted to rec.boats.electronics
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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= |
#30
posted to rec.boats.electronics
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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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