The Panbo Forum

Return to Panbo Forum main page »


"Low cost" Class B AIS

Vote 0 Votes

Having recently spent an interesting night dodging cargo traffic in the TSS between Spain and the Moroccan coast and realizing that I was probably below the radar of most vessels, I decided that it would be wise to add a Class B AIS transmitter to my installation.

After a quick trawl, I came away somewhat surprised at the high cost. Moreover, I was frustrated that I could not find a Class B transmitter, rather than a transponder or transceiver.

I already have received AIS data coming on to my network through a decoder integrated with my VHF and I have redundant sources for GPS data on the network.

Whilst avoiding single points of failure is a good thing, the high price of typical Class B transponders is making me doubt whether I really need to invest in yet another GPS receiver and another AIS receiver.

I know that there are arguments in favor of having an integrated GPS to avoid errors, however, many AIS transponders seemed to allow the position data to taken from the NMEA data stream, so the "avoid error" justification seems a bit weak.

I understand that Class A transmitters have to have knowledge of other traffic in order to bid for transmission slots and therefore by necessity the decoder element has to be integrated. However, if my understanding is correct, Class B devices are only using carrier sensing to avoid clashes and therefore do not need access to received AIS data nor indeed to the demodulated carrier.

I assumed that a Class B transmitter only device could be a relatively dumb - i.e. relatively inexpensive.

Is the current high cost just the product marketeers "premium for safety" or am I missing something?

6 Replies

  • Integrated receiver is a must have for transmitting, e.g. the precision timing to determine when the transmitter can start transmission within the next perhaps available time slot can't wait to traverse a 0183/2000/ethernet network. (Class B messages do share the same frequency and protocol, so that a Class B must have the same transceiver quality not to trounce Class A traffic)

    Large ship radar does scan down to the surface of the water. How about this to ** increase your chances somewhat ** of appearing on other ships radar ...

    A radar reflector has a benefit of increasing your visibility on boats that don't have AIS receivers.

  • A radar reflector, that is actually deployed, is also a conversation starter at a dock ... "what is that balloon in your rigging?"

  • Actually, having a passive radar reflector is a legal obligation where I come from.

    I must admit I have never thought of calling one of these large cargos to ask them if they can see me on their radar. It would be interesting to know.

    With reflection, transmitting AIS in the circumstances that got me thinking probably serves little purpose. It would be up to me to decide that I am on a course that presents a risk of collision and take action and not the 300m tanker that I am dodging. For this I only need AIS reception (and eyeballs and ears of course).

    Still, a full class B transponder would be a comfort in congested waters.

  • Aramis, there's a lot about AIS that most users don't know about. For instance, do you realize that all AIS transcievers must be able to monitor VHF Channel 70 and be ready to change broadcast frequencies and update intervals by order of an AIS Base Station? In short, an internal receiver is mandatory and not comparable to a simple and unregulated AIS receiver.

    Also, I think that there are at least five independent manufacturers of Class B transponders competing for market share. I really doubt that they fix prices.

  • Quite interesting. I was searching for AIS Class B prices when I accidentally stumbled upon this old discussion. Price is always a major consideration however, the paramount consideration should be, my safety and that others, which is many times just ignored.

    Ben was very correct to point out some of the hidden features of an CERTIFIED AIS Class B. Why then compromise your safety for a few dollars.

    I have just checked out this online web store

    The em-trak AIS Class B B100 is sold for USD449, shipped to your door step included in the price. The em-trak AIS Dual receiver is going for USD249. The price difference is only USD200. Will I compromise my life for this saving. NO!

    There are obviously cheaper units on the market. Please check their international certifications,quality and performances first !

  • Fortunately since my original post prices have come down massively. Back in 2015 a tranponder was closer to $800.

    The question at the 2015 prices was whether is was technically necessary to duplicate functionality that was already cost effectively present in other systems. It seems, from the knowledgable comments at that time that it was important for the GPS/TX/RX functions to be integrated.