AIS Poll

[Paul L]

Originally Posted by hodgmo

I don't understand how this comment, or the peeping Tom one, contribute anything positive to the discussion. How can receive-only AIS be anything but neutral or helpful in collision avoidance? In my case, I reluctantly installed the Standard VHF receive-only AIS in 2012 mainly because of peer pressure (and my previous VHF didn't have DSC). I was reluctant because I'd trusted my eyes and ears for decades without a problem. But after using it for some multi-day passages it was clear that the AIS almost always picked up transmitting boats long before I did, usually long before I did. Of course not all boats transmit so AIS doesn't replace watch keeping. My practice under way includes monitoring the AIS (CPA alarm set appropriately) and if a vessel appears with a course uncomfortably close to mine then I either: a) change course if I am the give way vessel, or b) if I'm the stand-on boat I hold my course and make a DSC call to the other boat (ship) to give my position, course, speed and confirm my intention is acceptable. My experience is that ships almost always answer (in a dozen or so mid-Pacific encounters, only once has a ship not responded reasonably promptly, although even in that case she did answer back after I gave way and we'd crossed paths). This method is certainly 'proper,' and in using it I consider myself part of the 'system,' as many others do similarly. While I can see benefit in being able to transmit, and I plan to add that capability eventually, I don't see any urgency to it, and I don't see why my practice, or even going without AIS, should be banned.

It sounds like you are another AIS convert. The cost of adding RX only AIS is so low versus its value that it is just foolish not to have it on a mom and pop or singlehanding cruiser.
Since the cost of rx/tx (receive/transmit) units has come down enough, any upgrade really ought to go rx/tx unless money is really tight.

[hodgmo]

Originally Posted by Paul L

It sounds like you are another AIS convert. The cost of adding RX only AIS is so low versus its value that it is just foolish not to have it on a mom and pop or singlehanding cruiser.
Since the cost of rx/tx (receive/transmit) units has come down enough, any upgrade really ought to go rx/tx unless money is really tight.

[tanglewood]

Originally Posted by hodgmo

I don't understand how this comment, or the peeping Tom one, contribute anything positive to the discussion. How can receive-only AIS be anything but neutral or helpful in collision avoidance? In my case, I reluctantly installed the Standard VHF receive-only AIS in 2012 mainly because of peer pressure (and my previous VHF didn't have DSC). I was reluctant because I'd trusted my eyes and ears for decades without a problem. But after using it for some multi-day passages it was clear that the AIS almost always picked up transmitting boats long before I did, usually long before I did. Of course not all boats transmit so AIS doesn't replace watch keeping. My practice under way includes monitoring the AIS (CPA alarm set appropriately) and if a vessel appears with a course uncomfortably close to mine then I either: a) change course if I am the give way vessel, or b) if I'm the stand-on boat I hold my course and make a DSC call to the other boat (ship) to give my position, course, speed and confirm my intention is acceptable. My experience is that ships almost always answer (in a dozen or so mid-Pacific encounters, only once has a ship not responded reasonably promptly, although even in that case she did answer back after I gave way and we'd crossed paths). This method is certainly 'proper,' and in using it I consider myself part of the 'system,' as many others do similarly. While I can see benefit in being able to transmit, and I plan to add that capability eventually, I don't see any urgency to it, and I don't see why my practice, or even going without AIS, should be banned.

Part of my point is that with receive only you are not participating, just listening. It may be just fine for you, but does nothing for other boats that would like to know what your are doing, just as you want to know what they are doing. That’s why AIS, by definition, is send receive.

And receive only AIS is VERY different from radar because with receive only AIS you are invisible to other boats. It’s what happens when you don’t participate.

Radar is fundamentally different because you can’t make yourself invisible to other boats. Just because your radar is “receive only” doesn’t impact other boats’ ability to see you.

[mikedefieslife]

Originally Posted by tanglewood

Part of my point is that with receive only you are not participating, just listening. It may be just fine for you, but does nothing for other boats that would like to know what your are doing, just as you want to know what they are doing. That’s why AIS, by definition, is send receive.

And receive only AIS is VERY different from radar because with receive only AIS you are invisible to other boats. It’s what happens when you don’t participate.

Radar is fundamentally different because you can’t make yourself invisible to other boats. Just because your radar is “receive only” doesn’t impact other boats’ ability to see you.

Yet having an AIS receive doesn't suddenly make you more invisible to other boats than not having it. If they could see you with their eyes before, they still can. If they could see you with radar, they still can.

Instead it makes you more aware, as you can very quickly see the speed and bearings of all craft that are transmitting (somewhere like Gibraltar this could be anything up to 20 boats), along with the MMSI of those craft. In that sense receive only AIS improves safety for craft that have transponders, as well as the receive only craft.

Obviously in a perfect world, all craft would have some form of transponder, and software would never allow two craft to meet unless they were set to certain modes.

[hodgmo]

Originally Posted by tanglewood

Part of my point is that with receive only you are not participating, just listening. It may be just fine for you, but does nothing for other boats that would like to know what your are doing, just as you want to know what they are doing. That’s why AIS, by definition, is send receive.

And receive only AIS is VERY different from radar because with receive only AIS you are invisible to other boats. It’s what happens when you don’t participate.

Radar is fundamentally different because you can’t make yourself invisible to other boats. Just because your radar is “receive only” doesn’t impact other boats’ ability to see you.

Mikedefieslife and others get it, but tanglewood doesn't.

As I clearly described, it is possible to 'participate' using AIS-receive, it's just requires more work. AIS-receive is good, transponding AIS is better. Class B AIS is good, Class A is better (depending on how 'better' is defined).

While I agree that AIS and radar are very different, in fact they are complementary systems, I find Tanglewood's radar example to be off-the-mark: It suggests that he hasn't encountered boats that don't show up - a not too uncommon occurrence, especially with older radar systems and if the other boat has no radar reflectors, and/or the seas are large. Twice, in lively conditions, after I contacted them to confirm my intentions were acceptable, I've had ships ask me to turn on my strobe so they could see me because I didn't show clearly on their radar, even though I fly a radar reflector.

I'm not going to waste any more bandwidth on this silly pedantic tangent to an otherwise useful discussion!

[chris in SG]

Originally Posted by hodgmo

Mikedefieslife and others get it, but tanglewood doesn't.

As I clearly described, it is possible to 'participate' using AIS-receive, it's just requires more work. AIS-receive is good, transponding AIS is better. Class B AIS is good, Class A is better (depending on how 'better' is defined).

While I agree that AIS and radar are very different, in fact they are complementary systems, I find Tanglewood's radar example to be off-the-mark: It suggests that he hasn't encountered boats that don't show up - a not too uncommon occurrence, especially with older radar systems and if the other boat has no radar reflectors, and/or the seas are large. Twice, in lively conditions, after I contacted them to confirm my intentions were acceptable, I've had ships ask me to turn on my strobe so they could see me because I didn't show clearly on their radar, even though I fly a radar reflector.

I'm not going to waste any more bandwidth on this silly pedantic tangent to an otherwise useful discussion!

No! Tanglewood gets it and others don't. It's not about 'receive-only' being unsafe or irresponsible. Surely it's about contributing to the system. Hodgmo and others know they can monitor Class A because all Class A vessels must transmit. If all Class B users opted for 'receive-only' equipment, then Class B AIS would cease to exist - there would be no Class B vessels registered and visible. It would then be merely a system for monitoring Class A - extremely useful but a different animal!

[ranger58sb]

Originally Posted by hodgmo

Mikedefieslife and others get it, but tanglewood doesn't.

As I clearly described, it is possible to 'participate' using AIS-receive, it's just requires more work. AIS-receive is good, transponding AIS is better. Class B AIS is good, Class A is better (depending on how 'better' is defined).

I suspect most everybody gets it.

An AIS receive-only system helps you; doesn't directly help me. If your system helps you avoid colliding with me, of course I'm grateful but if you were transmitting I might have been better able to help with the "dodge" process. If nothing else, by knowing your vessel name to facilitate VHF hailing. (Or you could hail me to discuss encounter.)

That's not a criticism. I do agree that receive-only is better than nothing, etc., and I know sometimes budget-driven choices are what they are.

-Chris

[CapnCrunch]

Originally Posted by FlyingScot

With regular Class B protocol, the transmission rate is fixed at every 30 seconds when the vessel is moving.]

At the risk of sounding stupid, I have never heard/read that a Class B AIS only transmits when the vessel is moving. Is this true? If so, that would explain why the barges passing me here on the Arkansas River when I'm in my slip dont "see" a signal from my AIS (Garmin Black Box).

[Paul L]

Originally Posted by CapnCrunch

At the risk of sounding stupid, I have never heard/read that a Class B AIS only transmits when the vessel is moving. Is this true? If so, that would explain why the barges passing me here on the Arkansas River when I'm in my slip dont "see" a signal from my AIS (Garmin Black Box).

Class B Stopped or sailing up to 2 knots: Every 3 Minutes
Class B Sailing faster than 2 knots: Every 30 Seconds

[chouliha]

Here is another reason to have a AIS transponder. There is an overdue vessel in French Polynesia waters that JRCC Papeete has put an advisory out on. yesterday. This sailboat was reported doing an inter island transit near to the atoll of Fakarava.

If the overdue vessel had an AIS transponder JRCC Papeete would be able to see the very last reported position via satellite subscription which all emergency centers have access to. In this case NO AIS data.

Amazes me that more vessels do NOT have AIS transponder while sailing. It is such a cheap upgrade and IMO so very useful.

Chuck

[Cat36Mahalo]

B transceiver

[tanglewood]

Originally Posted by chris in SG

No! Tanglewood gets it and others don't. It's not about 'receive-only' being unsafe or irresponsible. Surely it's about contributing to the system. Hodgmo and others know they can monitor Class A because all Class A vessels must transmit. If all Class B users opted for 'receive-only' equipment, then Class B AIS would cease to exist - there would be no Class B vessels registered and visible. It would then be merely a system for monitoring Class A - extremely useful but a different animal!

That's what I meant. I think it's important that people "contribute" by transmitting, not just listen in.


Personally I've never encountered a target that was transmitting AIS and wasn't also detectable on radar. And my radar is on 100% of the time I'm underway. The same can't be said the other way around. The bottom line is that your "receive only" device is only useful because of those of us who are transmitting. You are welcome, and it would be nice if you returned the favor. I think receive-only has served an important roll in teaching people what AIS can do via an inexpensive entry point. But once you are convinced, it helps everyone if you step up to the real thing at some point.

[Pizzazz]

Let's just go straight to the issue. AIS is useful but AIS transmit is expensive. There is no technical reason why is should be expensive, it is just a little bit of code to the radio firmware (ignore the detail about a second antenna, not needed on a recreational vessel) but I can see the argument that many recreational users will leave AIS transmit on all the time and this will become a problem in crowded marinas.

So, what can we do. One option is to spend $600 + install on a class B system but that has its problems as well, it is not powerful enough, it updates only every 30 sec and let's face it, it will be many years before, let's say half of the recreational boats install AIS transmit.

Another option is to leverage the DSC function. DSC in general is not used very much for routine calls (I think it is a bureaucratic issue, the menus are way too difficult to use). Would it be acceptable to use the DSC safety alert call to all ships to broadcast your position? Before you say no way, it was not designed for this, think about possible use cases:

- Low visibility, night sailing bad weather. Set your radio to safety call, all vessels, set the power to 1W (to limit the distribution) and send a simple message, this is SV xxx, so that ships around you know where you are (obviously do not do this in the marina). Send the message every 1 hour or when you shift ends, etc.

- Sailing offshore, before taking a nap, set power to 25W, send a message to all ships around you, SV xxx, captain will be sleeping for the next two hours, vessel not under command , wake up in 1.5 hours, resend message, sleep again - this is kind of a safety message when I think about it

I am curious what the Coast Guard will say about this use. On one hand, clearly outside the AIS system design and goals. On the other hand, it may be useful in some case and it costs nothing. Clearly, if cruising often one should get a proper AIS transmit device. By the way, are DSC calls picked up by satellites as well?

SV Pizzazz

[Paul L]

Originally Posted by tanglewood

That's what I meant. I think it's important that people "contribute" by transmitting, not just listen in.


Personally I've never encountered a target that was transmitting AIS and wasn't also detectable on radar. And my radar is on 100% of the time I'm underway. The same can't be said the other way around. The bottom line is that your "receive only" device is only useful because of those of us who are transmitting. You are welcome, and it would be nice if you returned the favor. I think receive-only has served an important roll in teaching people what AIS can do via an inexpensive entry point. But once you are convinced, it helps everyone if you step up to the real thing at some point.

Cases that come to mind as an exception to your experience are meeting on a blind curve on a river and in bad weather conditions such as a heavy downpour and large seas. The AIS signal is likely to be detected, the Radar target not likely to be detected on a small vessel.

[ranger58sb]

Originally Posted by Pizzazz

- Low visibility, night sailing bad weather. Set your radio to safety call, all vessels, set the power to 1W (to limit the distribution) and send a simple message, this is SV xxx, so that ships around you know where you are (obviously do not do this in the marina). Send the message every 1 hour or when you shift ends, etc.

- Sailing offshore, before taking a nap, set power to 25W, send a message to all ships around you, SV xxx, captain will be sleeping for the next two hours, vessel not under command , wake up in 1.5 hours, resend message, sleep again - this is kind of a safety message when I think about it

Easier to just spend the $$$ and install an AIS transciever. Eliminates watch standing screw-ups. And the AIS signal plots on the receiver's display (for their watch stander's situational awareness), something a DSC position report may or may not do.

It's easy enough for me to spend your money, of course.

-Chris