Eric.. Here's the reply from Siitech...
About Class B.
That is a very interesting question. Thank your reader that he raised it.
At fist I would like to say that definitely SiiTech Web VTS displays AIS Class B transponder. Please see the attached screen
AIS Class A has a triangle shape, but AIS Class B has a rectangle shape with an arrowhead.
Why we cannot see any Class B in New York harbor?
It could be several reasons:
1. The first one and the most common is that probably SiiTech doesn’t get any Class B ais messages from New York ais feeds. Marinetraffic displays only one Class B, but I believe there should be many of Class Bs, but not just the only one. We don’t know who provides AIS feeds for Marinetraffic, so we cannot compare SiiTech and Marinetraffic in this case. If we were sure that SiiTech and Marinetraffic get the same ais feeds then we could compare both sites. However there, in New York harbor, should be more than one Class B for sure.
2. Probably that is because of the AIS technology limitation: Class A can and has to reserve available slots to transmit ais messages, but Class B doesn’t have such rights. Class B cannot reserve any slots, so Class B waits for any free slot that could be left from Class As and only then transmits ais message. The priority to transmit was given Class A, because in such harbors as New York we have many vessels and even Class A theoretically could not find any slots to transmit ais messages. Again theoretically if we have a lot of Class As within one harbor then Class B could wait forever for any free slot to transmit its message.
3. It could be some issues with ais receiver which sends data to SiiTech or Marinetraffic. We don’t know if that is two channels or one channel ais receiver. There could be potential problems too.
4. Of course there could be some problems with web viewers too.
About ENC and Raster charts: Probably the user doesn’t have any firewall at home, but at work does. Please check if the firewall is open for HTTP 54 port, but not only for 80 one. We send ENC and Raster charts through HTTP 54.