Class B AIS, part 2
Today, I’m afraid, we must speak of “frequency agility.” Part of the Class A standard is that transponders must be able to change channels if ordered to by the presiding local coastal authority. The digital command is received on the VHF DSC calling channel, 70. As mentioned in the past only one port is currently using this function, Tokyo, and I’ve heard that even it may turn back to regular channels 87B and 88B. Nonetheless, in September the U.S. apparently surprised international AIS committees by demanding frequency agility in the Class B standard. (This may have something to do with the still unsettled dispute with Maritel over use of 87B in the States, but, again, another story). At any rate, this change will mean that Class B transponders are more complicated and more expensive than originally conceived, and slower to arrive. Actual transponders available by the end of 2006 for around $2,000 is now sounding realistic. It’s also possible that there will be non-agile Class B transponders that are not approved for use in the U.S.
Now, as promised, let’s noodle a bit about what the Class B standard will mean. My thoughts:
• Some bigger yachts are going to opt for Class A—perfectly legal for anyone to carry—because they’ll decide that the additional power and priority, plus things like ship-to-ship messaging (not in Class B), are worth the added expense and install hassle.
• I’m wondering if a single frequency receiver will be effective, especially in close quarters, when it’s only getting dynamic data every minute at best. Real time tracking starts to get unreal, but maybe not enough to make a difference.
• Overall, Class B is going to greatly enhance AIS. Isn’t there a famous computer postulate that puts the value of a network equal to the square of its users? Isn’t AIS a more-the-merrier—and safer—situation, even for the lurkers (receive only).
PS. For more details of Class B, check out this page at Y-Tronic, noting that the Class B standard is supposedly going to use “Carrier Sense”, not “SOTDMA”.
Now it’s the Si-Tex/Nasa/Nobeltec AIS receiver
October 18, 2005
Class B AIS, the devil’s in the details, part 1
October 26, 2005
One-channel-at-a-time receivers, another Class B problem?
December 7, 2006
Class B rollout, looking better, but mysterious
May 21, 2009