ONWA's disturbing statement about AIS


New member
Hi all!

I was browsing through an ocean of info to find which AIS would best suit my needs, when I stumbled upon this rather disturbing statement from ONWA, leader of cheap AIS products, in the FAQ section of their KS-200A black box (type B transponder).


  1. Q : Why is it that I cannot see the ship nearby in the Automatic Identification System (AIS) screen, though I see it on the sea?

    • A: There are two classes of Automatic Identification System (AIS) devices: Class “A” Transponder and Class “B” Receiver. Class “A” transponders are those with built-in VHF transmitter and receiver. This means that the device can transmit and receive vessel information to and from its own vessel. On the other hand, Class “B” receivers are only able to receive vessel information from other vessels which has AIS transmitters. Thus, vessels with Class “B” AIS devices cannot be seen by other vessels, it can only receive information from other AIS devices."

... bam!

So according to a leader in AIS technology, type B is only a receiver?

I kind of figured out by now that this statement is pure ignorance!

But... how far does this go?? Is any of you using, or knows someone who uses the ONWA black box?

Have you ever tried to check if you could see it from another ais receiver?? And not only from your own?

Seriously, if there is thousands of sailors that genuinely believe they can be seen in pitch black thanks to a box which is no more of a receiver... how long before something bad happens?!

/end of crazy complaint

Thanks for your attention ;)

Source (click on FAQ) :


That's just crap tech support, the question is asking why they don't see a ship on AIS that they can physically see, which can be any number of reasons.  If the ship is transmitting any unit should pick it up. It looks like the response is mangling the difference between receive only units and receive transmit units or assuming the "ship" in question is receive only, or Google translate wasn't working.

Have seen alot of people have issues with cheap AIS especially when used with existing VHF, can mess with the radio, not being able to transmit well or hear anyone.

Last edited by a moderator:


New member
Fleetwood said:
All large and commercial vessels (details depend on jurisdiction) must have a Class A transponder, these days having at least a Class B receiver is a good idea if going offshore so you can "see" these ships. Install a Class A if you want to be seen.
Wait a minute...

I agree with most of what you say, but your last sentence... "Install a class A if you want to be seen". Are you implying that you can't be seen with an ais class B "transponder" (not a receiver, a transceiver), by the surrounding yachts in range of your device?

Because this isn't what the retailers say, and doesn't seem to be most sailors' opinion...

And why invest in a class A when a class B is enough of a safety to be seen on a decent range, specially with the new 5W technology that can be relayed by sattelites?

For the records, a class A transceiver is 10 times more expensive! I don't know any sailor that ever invested in a class A AIS. (Maybe because I don't know any superyacht owner...)

Could you please develop your advice? And also let me know what your knowledge in AIS technology is?

Sorry to be so suspicious, but I've seen people giving me advices on subjects they don't know anything about too many times, just to sound like they know better.

Because the advice you give me goes against anything I've found anywhere else, and sounds just like you agree with the above statement by ONWA, which is highly controversial.

But I'd be truely interested to know if the whole class B transciever is inefficient, and only the AIS type A owners can be seen, as claimed by ONWA



Super Anarchist
Looks like Onwa should get someone who can actually comprehend English to revamp that FAQ. Its entirely specious with the writer not understanding that a Class B AIS is -not- simply a receiver.

Onwa has some wide exposure outside the US (where their transceivers are not FCC approved as the users can enter transmitter data), and comments on YBW and elsewhere are claiming good use from the various models of Class B AIS transceivers.

I do like their idea of combining the AIS with the chartplotter...




Super Anarchist
Boston, MA

this page has good info. One of the primary differences between Class A and B is their transmit power - 12.5w for A and 2w for B. The frequency ranges are 100% the same so it is absolutely not true that a Class A can't "see" a Class B. they just can't seem them from as far away.



George Dewey

Super Anarchist
Charleston, SC
I have a friend who is also trying to save a few bucks, and I'm looking at this for him. My preference would be a SiTex MDA-5H but, not my money. He has a dedicated AIS receiver already, so he is looking for something that will just transmit. This may be as close as it gets, and it's on Ebay for $210.

But, does it work, and reliably? I do understand he'll need a splitter to go with this, so not much savings really.

George Dewey

Super Anarchist
Charleston, SC
Yeah... No. My boat is equipped with the older class B AIS transponder. I'll upgrade to an MDA-5H in the spring. This guy recently had a serious accident, and it's impaired his income, at least for now. He won't be crossing any oceans soon anyhow, but it's still handy for coastal racing.

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