"A" versus "B" AIS - worth transmitting?

[CaptTom]

I was going to say I'm sorry for questioning the claim of RAM status, but I've changed my mind.

Instead, I'd like to thank those who came to the defense of the "real" COLREGs. Folks with far more time under their keels, and higher tonnage licenses, than I.

Allowing these myths to be perpetuated, unchallenged, is why so many sailors think they always have "right of way."

Some may find the rules too legalistic, or think they can bend the rules to suit their preferences. But the reality is, we're all safer out there when we all know, and abide by, the SAME rules.

[Kenr74]

Not to interrupt a good fight, but since the consensus is that it IS worth transmitting, I would be interested in equipment recommendations. I am replacing my VHF, and am interested in adding AIS. My first instinct was to get VHF with AIS receive (too bad Standard Horizon’s effort to do both transmit and receive in a VHF failed to get approval). If I get a separate AIS transceiver (so as not to bring the ire of CarlF down on my head) what should I do about the VHF? I only ask because it seems one of the advantages of AIS is being able to contact vessels with a DSC call. Obviously one could manually enter the mmsi into the VHF from the AIS display, but that seems tedious and error prone. I know networking would make it possible to share AIS information with the VHF, but has anyone done this in practice? If a VHF does not have its own AIS capabilities, would the display be usable for sorting through AIS information? Or would it just be better to get a VHF with an AIS receiver for the purpose of contacting vessels, and a transponder to transmit? I’d appreciate thoughts from others.

[svmobert]

Originally Posted by Kenr74

Not to interrupt a good fight, but since the consensus is that it IS worth transmitting, I would be interested in equipment recommendations. I am replacing my VHF, and am interested in adding AIS. My first instinct was to get VHF with AIS receive (too bad Standard Horizon’s effort to do both transmit and receive in a VHF failed to get approval). If I get a separate AIS transceiver (so as not to bring the ire of CarlF down on my head) what should I do about the VHF? I only ask because it seems one of the advantages of AIS is being able to contact vessels with a DSC call. Obviously one could manually enter the mmsi into the VHF from the AIS display, but that seems tedious and error prone. I know networking would make it possible to share AIS information with the VHF, but has anyone done this in practice? If a VHF does not have its own AIS capabilities, would the display be usable for sorting through AIS information? Or would it just be better to get a VHF with an AIS receiver for the purpose of contacting vessels, and a transponder to transmit? I’d appreciate thoughts from others.

https://www.sea-tech.com/2018/12/14/...on-that-works/

[MartinR]

Originally Posted by carioca

The Houston/Galveston VTS only picks up Class A AIS. Many large commercial vessels transiting the Houston Ship Channel will turn off the reception of Class B signals.

Commercial vessels can NOT turn off class B reception. I have never been on any vessel where this was possible, and it would definitely be against regulations. Class A targets are prioritised in all systems, if too many targets, class B is purged. But if the class B target is close enough it will show up. So, no worries...

[Dockhead]

Originally Posted by Watermann

First of all, this shouldn’t be a personal thing. Lighten up a bit!!

In the “real world” I am the guy on watch on one of those cargo ships or tugs. Legalities aside, from my perspective, a sailing vessel claiming RAM through AIS nav status without the associated lights and day shapes will be ignored as to having such status. AIS nav status doesn’t mean squat. Yes, it’s unprofessional to not update it but rarely is nav status brought up by watchstanders anyways. We’re generally looking at name and CPA. That’s it 99% of the time.

Everyone at my academy took basic sailing in dinghies and our waterfront program consisted of one of the best college sailing fleets in both dinghies and keelboats. I myself have sailed all my life and have owned multiple boats over the years. I haven’t done much blue water but can certainly appreciate when someone is in a crappy weather situation.

A captain’s discretion must still be justified. I still maintain that is not a RAM situation. It goes against everything I’ve ever read, experienced and have been taught. At best, you’re maybe NUC.

But it’s not worth arguing anymore.

Rule 2 allows us to bend the Rules, and even break them, if it is necessary for the sake of safety.


Thus I am all in favor of single handers heaving to and showing NUC when they sleep (far from traffic areas of course), although clearly NUC status does not cover voluntary sleeping. I am in favor of it because the Rules don't allow failure to keep watch, but single handers cannot comply with this, and therefore, doing the best they can, showing NUC accurately communicates what other vessels can expect from you. Accurate communication is key to all this.


Showing RAM because you're under sail is quite a different situation, and will merely create mass confusion. Are you sailing vessel? A dredger? A survey vessel? Or what? Confusion is the enemy of safety in collision avoidance situation. Do not do this, please. Not only is it clearly not what RAM means, but it does not communicate anything useful. The nav status of "Under Sail" is what you want, and other vessels understand that vessels under sail cannot maneuver in all directions -- that's kind of the WHOLE POINT of "Under Sail" status. Showing RAM would be a real WAFI move, not helpful to anyone.


And as Watermann correctly states, and this is important -- broadcasing some special nav status over AIS is meaningless without the appropriate lights and shapes. The lights and shapes have legal status; AIS navstatus does not (AIS is not any legal part of the Rules at all). Showing one nav status via AIS then without the corresponding lights and shapes is double WAFI. This will just make commercial mariners think we are all idiots. Please do not do this.

[billknny]

Originally Posted by Kenr74

... it seems one of the advantages of AIS is being able to contact vessels with a DSC call.

As far as I have seen, DSC is totally unused. I have heard a few (less than 5) DSC distress calls, and every one turned out to be an accidental activation, or a kid pushing buttons (does that count as "accidental?")

I have never been the originator or receiver of a DSC call. Most of the times I have had the need to initiate a conversation with large commercial shipping was in remote areas with very little radio traffic. In congested areas, I just stay clear, and keep a close ear on Channel 16 and in many ports, 13. If it is a VTS port, I'll listen to that too. I do broadcast AIS "B", but have never had anyone use DSC to get my attention.

I know how DSC works, can can use it, but have never seen the value of it. Is there any boat out there who has their DSC turned on who does NOT respond to a standard radio hail?

Does anybody out there use DSC regularly? Do you get responses if you make a ship to ship call? Has anyone ever received a DSC call from a commercial ship?

[Dockhead]

Originally Posted by MartinR

Commercial vessels can NOT turn off class B reception. I have never been on any vessel where this was possible, and it would definitely be against regulations. Class A targets are prioritised in all systems, if too many targets, class B is purged. But if the class B target is close enough it will show up. So, no worries...

I have spoken with a lot of commercial mariners about this, and not one of them ever said that he filtered Class B targets or had ever heard of anyone who did, if it's even possible. They are eager to know everything out there which they might run into, as doing so can have devastating effects on their careers, and they are very eager indeed to see your AIS broadcast, so I agree with this -- don't worry about Class B filtering.


That being said, the legacy Class B protocol, based on Carrier Sense TDMA, has some severe disadvantages in how messages are prioritized, and in a really crowded area it is possible that your Class B broadcasts might not get through every broadcast, which is only once in 30 seconds.


So for anyone buying a new AIS set, I strongly recommend going for one of the new SOTDMA Class B sets, which use the same network protocol as Class "A" (SOTDMA or Self Organized TDMA), and which, besides that, can broadcast more frequently like Class A does (up to once every 5 seconds), and which, on top of the other advantages, has more power at 5 watts vs. 2 watts.



I'll be switching to one of these myself during my winter refit.

[svmobert]

Originally Posted by Sea-TechSystems

https://www.sea-tech.com/2018/12/14/...on-that-works/

To elaborate, I just wrote up the above blog post the other day that attempts to describe how you can make the two work together simply and without the potential issues. You can combine certain VHF radios with AIS transponders quite well, but you need to make certain choices about how you want to use it, and how much $$ you are willing to spend.

[Dockhead]

Originally Posted by billknny

As far as I have seen, DSC is totally unused. I have heard a few (less than 5) DSC distress calls, and every one turned out to be an accidental activation, or a kid pushing buttons (does that count as "accidental?")

I have never been the originator or receiver of a DSC call. Most of the times I have had the need to initiate a conversation with large commercial shipping was in remote areas with very little radio traffic. In congested areas, I just stay clear, and keep a close ear on Channel 16 and in many ports, 13. If it is a VTS port, I'll listen to that too. I do broadcast AIS "B", but have never had anyone use DSC to get my attention.

I know how DSC works, can can use it, but have never seen the value of it. Is there any boat out there who has their DSC turned on who does NOT respond to a standard radio hail?

Does anybody out there use DSC regularly? Do you get responses if you make a ship to ship call? Has anyone ever received a DSC call from a commercial ship?

It saddens me to say that my experience has been the same as yours.


It's really a shame because DSC is so extremely useful. I use it a lot when communicating with friend's boats and between the mother ship and my own handheld. I use it with the Coast Guard, who are always surprised to get a DSC call, apparently because almost no one uses it, but they do answer.


Almost never does a ship answer a DSC call. They respond to voice calls on 16. Once I had a difficult situation with a large passenger ferry, who refused to answer my voice calls. Apparently because I was mispronouncing the Swedish name, the barsteward. He did finally answer a DSC call. That's about the only time I recall ever getting a ship to answer a DSC call.


I have never received a DSC call from a ship, but I did receive one once from the Finnish Coast Guard, warning me to stay out of Russian waters off Gogland (formerly known as Suursaari). I knew where I was going -- I was tacking upwind and about to change tacks towards Kotka -- but I was grateful for the call.



I wish everyone used DSC more. It would significantly de-clutter Channel 16 and make calling easier and less prone to errors of identification.

[tanglewood]

Just a few comments.


I think saying that an AIS device can filter targets is a bit of a misnomer. It's the display device that filters what it displays. Now some AIS devices are both a transceiver and a display, which contributes to the confusion. But if you filter targets in the display, I seriously doubt the device will stop sending those target reports over 0183 or N2K to other devices that want to display them....


I personally think the whole "big boats filter you out" is a myth, but it is true that some display devices have the ability to filter out Class B. Furuno's professional radars, for example, as well as Coastal Explorer. I have owned both and can confirm first hand. That said, I think only a fool of a captain would ever do that. Their job it to not collide with any other boats, not just select other boats.


What filtering does make sense is based on speed, distance, and possibly status. That's the solution to clutter from moored boats. Filter them out because they are not moving. If your display is too stupid to do that, get a better display. Don't ask the whole world to turn off their AIS because you have a dumb display. Besides, Class A AIS are supposed to be left on all the time.


Class A has some extra features, but don't underestimate the effort require to correctly install one. Class B will work stand-alone without any input data from other instruments on the boat. Class A will not. Class A requires heading, rate of turn, SOG, COG, and position from you boat's primary instruments. The Class A's built in GPS is a backup only, and the device will alarm continuously if the requisite input data isn't present all the time. Also, Class A requires true heading as an input, and that can be harder to get than you might think. Magnetic compasses report magnetic heading, not true heading. And even if your display can correct to true, it doesn't mean that true heading is present on 0183 or N2K. It just means the display is calculating it for it's own use. The only devices that produce a native true heading are sat compasses and gyros.

[Cpt Pat]

Originally Posted by Dockhead

So for anyone buying a new AIS set, I strongly recommend going for one of the new SOTDMA Class B sets, which use the same network protocol as Class "A" (SOTDMA or Self Organized TDMA), and which, besides that, can broadcast more frequently like Class A does (up to once every 5 seconds), and which, on top of the other advantages, has more power at 5 watts vs. 2 watts.



I'll be switching to one of these myself during my winter refit.


Attachment 182341

Just jumping in to concur with this post. If you are buying a new Class B, be sure to get one that uses SOTDMA protocol. Another downside of carrier sense (CSTDMA) is that any high level of broadband noise in the vicinity of your AIS antenna (like many of the noisy LED tri-color lights out there) is much more likely to inhibit transmission of your data. A CSTDMA transponder may interpret the noise as a continual carrier and stop transmitting. I had this problem myself. When I upgraded to a SOTDMA transponder, the problem was resolved (though I still had limited AIS reception range with the light on - which I later replaced).

See the USCG safety alert for details about LED interference with AIS & VHF: https://www.dco.uscg.mil/Portals/9/DCO%20Documents/5p/CG-5PC/INV/Alerts/1318.pdf?ver=2018-08-16-091109-630. By the way, the USCG procedure in that alert won't work with PLL-based receivers - like Standard Horizon's because the squelch will only open with a coherent carrier - not with random noise. It's better to tune in the weakest NOAA weather station, and then turn on your LEDs. If the station vanishes, you have a noisy LED.

Once you have installed your AIS unit, you can verify the programming by using this link to the USCG Verification Service: https://www.navcen.uscg.gov/aisSearch/index.php. (Obviously that only pertains to stations in range of a US VTS station). Any programming errors will be flagged in red. Wait one weekday after powering up your AIS before looking at the results.

[IslandHopper]

DSC is as distracting and time consuming as texting while driving, other than mandatory testing of equipment to make sure emergency DSC calling is functional the majority of commercial mariners will not use it for general calling.

Most equipment is not located in the best of positions and the vast majority of it is time consuming and clumsy to use at best, the key pads are terrible, using voice keeping it short and to the point is still the preferred way.

[Cpt Pat]

Originally Posted by IslandHopper

DSC is as distracting and time consuming as texting while driving, other than mandatory testing of equipment to make sure emergency DSC calling is functional the majority of commercial mariners will not use it for general calling.

Most equipment is not located in the best of positions and the vast majority of it is time consuming and clumsy to use at best, the key pads are terrible, using voice keeping it short and to the point is still the preferred way.

Yeah. the DSC user interface on most radios is terrible. Even sending a "designated" (with a reason) DSC distress call, on my Standard Horizon, is as complicated as programming a VCR (for those old enough to remember). It's still useful for crew/passengers though to tell them: "If I'm unconscious or overboard, press this button and then make a voice call." At least it sends the lat/lon, which a newbee might not know how to provide.


All that assumes the radio is receiving GPS data and the MMSI is programmed.

[Kenr74]

Originally Posted by Sea-TechSystems

https://www.sea-tech.com/2018/12/14/...on-that-works/

Wow, that is fantastic write up that very much answers my questions. Thank you very much for providing that.

[Kenr74]

Originally Posted by billknny

As far as I have seen, DSC is totally unused. I have heard a few (less than 5) DSC distress calls, and every one turned out to be an accidental activation, or a kid pushing buttons (does that count as "accidental?")

Thanks for the input. I am new(wish) to sailing, and have yet to venture into very congested areas. In the sailing I have done on the Great Lakes, it seems all but impossible to get anyone to answer the radio on 16. I had hoped DSC would have better success. At least with AIS, you can call by name instead of, "Hello big ship bearing down on me...."