On Mar 22, 2013, at 12:21 PM, "Della Barba, Joe" <joe.della.ba...@ssa.gov> wrote:
> Nothing stopping anyone from using Class A but the $$$$. True. But I stand by my statement, using the word "generally". Here's more on the differences between Class A and Class B: > The International Maritime Organization (IMO) and the International > Convention for the Safety of Life at Sea (SOLAS) requires AIS to be fitted > aboard international voyaging ships with gross tonnage of 300, cargo ships of > 500 gross tonnage and all passenger ships regardless of size. > > There are several important functional differences between AIS Class A and > Class B transponders. > - Class A meets the requirements of the IMO AIS carriage requirements and > is standardized in SOLAS, while the Class B provides capabilities which are > not fully compliant with IMO requirements. > - A main difference is the data communication technology; Class A units > utilize Self-Organizing Time-Division Multiple Access (SOTDMA) technology. > This technology ensures that VHF transmissions of different transponders do > not occur at the same time by synchronizing their data transmission to an > exact timing standard, providing that no transmissions are missed. Class B > units utilize Carrier-Sense TDMA (CSTDMA), which listens to the AIS network > to determine if a slot is being used. Once the unit determines that the slot > is open, it powers up its transmitter and broadcasts a 1 slot position > report. The Class B is also required to listen for reservations from base > stations and comply with these reservations. If the unit cannot find an open > slot, it will not broadcast. > - The reporting intervals are lower with a Class B transponder than a Class > A transponder. > - The transmitted AIS data from a Class B transponder is limited; a Class A > transponder transmits and receives all required AIS data > IF you go Class A, be prepared to be constantly changing your AIS data as far as Navigational Status (underway using engine, underway sailing, moored, at anchor, etc.), as this data is required to be in the Class A AIS datastream. Class B is a lot simpler, and really geared toward recreational use. Class A transponders also use significantly more power than Class B, not a non-issue to sailors. I don't see any benefit to spending the extra $$$, unless you think you'll be more visible to large vessels as a Class A vessel; that's a subject still being debated: http://www.panbo.com/archives/2010/04/the_class_b_ais_filtering_myth_revisited_arrrrrgh.html http://www.panbo.com/archives/2010/12/class_b_ais_filtering_the_word_from_dr_norris.html Fred Street -- Minneapolis S/V Oceanis (1979 C&C Landfall 38) -- on the hard in Bayfield, WI :^(
_______________________________________________ This List is provided by the C&C Photo Album http://www.cncphotoalbum.com CnC-List@cnc-list.com
