AIS Transponder: Yes or No

[SailFastTri]

Originally Posted by captainKJ

The IP of this web site is 173.192.60.130. Google answers to 74.125.226.115. If we had a conversation about multiple web sites do you think it would be more clear to everyone involved if we describe them by name or number?

apples and oranges. web site and AIS are 2 different things.

Yes they are, but the point I was making is that people readily recognize and respond to names not long strings of numbers. That's why ships and web sites have names.

[s/v Jedi]

Originally Posted by SailFastTri

So while a general-purpose marine VHF antenna isn’t optimized for AIS specific frequencies, it is designed to work very near those frequencies.

The worry isn't the frequency range of the antenna... it's that only one device can transmit at the same time. All those fancy auto-switches prefer VHF over AIS which means that your AIS transmissions are blocked when you talk over the radio. Not good so dedicated antenna on transponder is the way to go (and cheaper too).

cheers,
Nick.

[CarinaPDX]

Hmmm, a little bad info here:

xymotic: ALL Class A and Class B type approved transceivers listen to both frequencies - it is only the cheap receivers that listen to just one. The dynamic packets (position, course, and speed identified by MMSI) for both A and B are the same format and are received just fine by all approved units. The problem was that the early Class A units and MFD displays were produced before a standard was agreed upon for the (abbreviated) Class B static messages (tying MMSI to the ship's name, hailing port, etc). All Class A units should have had required updates by now but many older chartplotter displays used with Class B and receivers don't recognize the Class B static messages. The result is that positions are reported by MMSI without further information on these older displays. Collision alerts should work, unless someone screwed up the software. Personally I think it is a crime that MFD manufacturers are refusing to offer updates for older AIS-capable displays.

captainKJ: 4 ft seas isn't much of a test. Very little of the time I have spent out in open ocean is anything like that. The norm is 6-8 ft, or even 10-12. I will stand with my experience querying passing ships - they just don't pick up my radar reflector in rough seas. The theory is actually pretty simple. As wave heights increase two things happen: 1) the radar return off the waves increases, and 2) the radar return off a small boat decreases (it is hidden from view more often). At some point the boat's signal is simply too small to register. Your experience with a lobster boat is an entirely different kettle of fish: in order to find those pots you must have the adjustments set sensitively. The best I can tell most ships have the thresholds set high to avoid false alarms on their guard zones/ARPA. Whatever the case, it is the ships that told me that they couldn't see me, and I'll take them at their word.

[xymotic]

None of that is relevant to what I said.

Class A transmits every few seconds. Class B usually only transmits every 30 seconds. So it's quite easy to miss a message or two.

And I admit my info on it is a bit dated, but my understanding is that Class A receivers do not have to monitor class b messages At All. So like I said I think most operators will not mess with it, but it is possible for them to ignore class B completely.

Originally Posted by CarinaPDX

Hmmm, a little bad info here:

xymotic: ALL Class A and Class B type approved transceivers listen to both frequencies - it is only the cheap receivers that listen to just one. The dynamic packets (position, course, and speed identified by MMSI) for both A and B are the same format and are received just fine by all approved units. The problem was that the early Class A units and MFD displays were produced before a standard was agreed upon for the (abbreviated) Class B static messages (tying MMSI to the ship's name, hailing port, etc). All Class A units should have had required updates by now but many older chartplotter displays used with Class B and receivers don't recognize the Class B static messages. The result is that positions are reported by MMSI without further information on these older displays. Collision alerts should work, unless someone screwed up the software. Personally I think it is a crime that MFD manufacturers are refusing to offer updates for older AIS-capable displays.

captainKJ: 4 ft seas isn't much of a test. Very little of the time I have spent out in open ocean is anything like that. The norm is 6-8 ft, or even 10-12. I will stand with my experience querying passing ships - they just don't pick up my radar reflector in rough seas. The theory is actually pretty simple. As wave heights increase two things happen: 1) the radar return off the waves increases, and 2) the radar return off a small boat decreases (it is hidden from view more often). At some point the boat's signal is simply too small to register. Your experience with a lobster boat is an entirely different kettle of fish: in order to find those pots you must have the adjustments set sensitively. The best I can tell most ships have the thresholds set high to avoid false alarms on their guard zones/ARPA. Whatever the case, it is the ships that told me that they couldn't see me, and I'll take them at their word.

[goboatingnow]

Originally Posted by captainKJ

A commercial ship's radar is simply not adequate to pick up small sailboats except in calm conditions

This is the BIGGEST BUNCH OF CRAP I HAVE EVER SEEN. The radar we use can pick up lobster bouys in 4 foot seas. I have worked private yachts, commercial ships and have my own sailboat. I would choose radar before AIS. Make sure you have a BIG radar reflector or 2 onboard your sailboat.

Captainkj, you make very uninformed posts. Recently I just delivered a boat without AIS but with radar and a reflector , I was sailing through some crowded water ( southern Portugal, straits of gib ).
Firstly less then 1 in 5 ships responded to calls giving them their lat/lon or any geographical location.

Only in the open sea where it was clear I was referring to them did they respond. In the three cases , two were very modern high spec cruise liners. One had a faint return , but not enough that his ARPA could track me. The other two could see my lights but has no radar return that they could discern. The conditions were moderate chop to about 40 foot swells.

The fact is as is constantly proved large ships do not see small GRP yachts.

Crossing the busy shipping lanes near the approaches to GIB, where there was a dense concentration of shipping , none zero , nada responded to geographical calls. They all chatted to each other by ships name , but I suspect watchs dont respond to calls that don't specifically identify them.

Bottom line , AIS transceivers are the best thing since sliced bread , it's inconceivable that a modern yacht costing $$$$$ doesn't carry a 500 dollar vast improvement to safety.

Don't go sailing without one.

Dave

[SimonV]

You should read the report on Jessica Watsons prang. Ais is good but most A class can turn down their B recieve due to all the clutter it can produce, they may still see you but.... I will stick to recieve AIS only and use the radar if thing get bussy.

[SimonV]

and another thing how come the Arabian Sea, Gulf of Aiden and the Red Sea are AIS dead zones.

[barnakiel]

Originally Posted by jeffrobbins

(...) I've never tested any of the budget receivers or integrated-into-the-VHF receive-only models, so I can't say whether they would meet the Class B specifications or not. (...)

I did.

Vis-a-vis three online ais viewers we can see all 'B' vessels displayed.

Can't say if they meet Class B requirements but can say this one works as advertised.

Cheers,
b.

[offgrid64]

how about an international regulation that any ship which runs down a small vessel, if at fault, gets a 10 million dollar fine which goes directly to supplying free ais systems to all registered boats over 25 ft. in it's region? Or a very small fee for shipping companies per year to help subsidize ais systems. I don't mind paying an extra 1/100 of a penny for the imports.
I currently don't have an ais system but I do receive whenever you can get internet signal on smart phone or verizon hot spot, even in the ocean you can go here:
Live Ships Map - AIS - Vessel Traffic and Positions

[Auspicious]

Originally Posted by SailFastTri

No doubt Furuno was giving you good advice to optimize your installation, but if you already have a spare VHF antenna it can be used for AIS with very good results.

It is much more likely that Furono was saying that splitters are a bad idea.

Originally Posted by xymotic

And I admit my info on it is a bit dated, but my understanding is that Class A receivers do not have to monitor class b messages At All. So like I said I think most operators will not mess with it, but it is possible for them to ignore class B completely.

Can you back that up with verifiable fact? This rumor pops up periodically but has no basis. Some older AIS A receivers had trouble with Class B fixed data (like boat name) but all showed the variable information like position, course, and speed.

Originally Posted by SimonV

You should read the report on Jessica Watsons prang. Ais is good but most A class can turn down their B recieve due to all the clutter it can produce, they may still see you but.... I will stick to recieve AIS only and use the radar if thing get bussy.

Again - where is the evidence of ANY Class A receiver ANYWHERE that filters Class B? Don't mind me - Bob Ellison at Panbo would love to hear about it.

[David M]

Originally Posted by SailFastTri

The marine VHF spectrum is 156.000 through 161.925 MHz. Marine VHF antennas are tuned to accommodate that fairly broad band. AIS uses two channels at the top of the VHF range: 161.975 MHz, and 162.025 MHz. So while a general-purpose marine VHF antenna isn’t optimized for AIS specific frequencies, it is designed to work very near those frequencies.

No doubt Furuno was giving you good advice to optimize your installation, but if you already have a spare VHF antenna it can be used for AIS with very good results. In a controlled test you could measure a performance difference, but in the real world you'd probably never know the difference without some kind of measurement capability.

If someone could point to a test showing the performance difference with an AIS-tuned antenna vs. a VHF general antenna I'd be very interested. If the difference is more than 15 or 20% I'd be very surprised.

BTW -- my West Marine AIS 1000 transceiver recommends use of a "VHF antenna". It has a self-test diagnostic which would show a red error light and shut down radio transmission if the antenna's VSWR is out of acceptable range (1.5:1). I'm using a standard 3db dedicated VHF whip and have never seen that light, and based on tests using marinetraffic.com and other vessels I know my range is very good and meets "normal" AIS Class B expectations.

As I said in an earlier post, I tried using a standard VHF antenna and it received but did NOT work for transmitting. After purchasing an AIS specific VHF antenna it DID work for transmitting.

Why this is I do not know, but for a FURUNO CLASS A AIS transceiver, Model FA150, this is the case. Not any VHF antenna will work with this specific hardware...period.

Perhaps the difference is that for a Class B AIS transceiver any VHF antenna will work but for Class A AIS, a VHF antenna dedicated for Class A AIS is required?

[Auspicious]

Originally Posted by David M

As I said in an earlier post, I tried using a standard VHF antenna and it received but did NOT work for transmitting. After purchasing an AIS specific VHF antenna it DID work for transmitting.

You had some other problem. There is no technical reason for the scenario you describe.

[David M]

What other problem? Perhaps you misread my earlier post? It has always been about the hardware I described.

I know my experience. Furuno's tech support number is 888 834-9330 if you do not believe what I experienced nor believe the antenna requirements for my particular hardware. Ask for Larry or John, both of which helped me to solve the transmitting problem.

[Bash]

Originally Posted by CarinaPDX

A commercial ship's radar is simply not adequate to pick up small sailboats except in calm conditions.

My guess would be that there are alternative reasons for your lack of success getting ships to respond to hails on the VHF. It's highly unlikely that ship owners would make such a substantial investment in a large vessel and not equip in with an adequate radar.

The fact of the matter is that ships carry radars far more powerful than the 2kw or 4kw units most recreational boats use. And most ships have multiple units in use simultaneously. They get far better data than most of us imagine.

[Auspicious]

Originally Posted by David M

What other problem? Perhaps you misread my earlier post? It has always been about the hardware I described.

I know my experience. Furuno's tech support number is 888 834-9330 if you do not believe what I experienced nor believe the antenna requirements for my particular hardware. Ask for Larry or John, both of which helped me to solve the transmitting problem.

Sure. I'll give them a ring on Monday. I'd like to hear what they have to say. There is simply no difference between an "AIS VHF" antenna and a conventional marine VHF antenna. There is no match difference. It simply doesn't work that way.