Please turn your AIS off when docked/moored/anchored

[goboatingnow]

To address several issues

here would be no way I would rely my class B signal to help a commercial ship navigate around me - therefore whether I had a transponder or not was not an issue. I can always see that commercial ship and take full responsibility for staying well away from it no matter its intentions.

Well that isnt the COLREGS approach, and AIS always is a "Help". Thats all it is really a, an "aid". It does not substitute for good seamanship.

I have described TWO situations (within a couple of days). One was sailing by NYC (at about midnight) where my AIS was only able to transmit about half of its scheduled messages - that would seem very clearly to imply that class B IS near its technical limits in some particularly crowded areas.

CLass A can be managed control access and has inbuilt methods to reuse slots etc, or slot accessed can be controlled by a controlling station. Also CLass A has the concept of physical transitional boundaries where automatically Class A changes access methodology ( CLass A has SOTDMA, ITDMA, RATDMA, FATDMA as access methods!), change.

Its also worth noting that the technicals provisions are there for CLass B 'SO' transceivers to also participate in the Self Organised TDMA access methodologies. Im not sure if there are any CLass B 'SO's out there.

Hence Evans , given the nature of CLass B 'CS" ie CSMA-TDMA. IN essence this means that (a) it can only use one slot, (b) it only seeks out a free slot by sensing activity in that slot. (c) the local 'competent' authority can control class B 'CS' in its area of operation , in essence giving higher priority to CLASS A and hence lower to Class B 'CS'.

Furthermore since CLASS B is subservient to class A, in areas of high Class A activity , class B 'CS; is designed to essentially 'fail'


Hence in high density areas several issues can combine to prevent your Class B 'CS' device from transmitting

1. The presence of large number of Class A devices,

2. The presence of large numbers of Class B devices

3. The commands being sent from the base stations. ( including Quiet commands, that essentially shut down Class B, or reduced interval reporting commands )

4. The inherent construction of the Class B protocol, ie a total of only 10 Candidate periods out of the whole available Transmission Interval.


What this means Evans is that CLass B was designed to be overloaded and to in effect stop working. Thats not a fault of the system.

Furthermore, merely reducing the number of class B units transmitting does in fact not guarantee that your class B unit would in fact get through any better. in a large port area, there simply maybe no ( or few) Candidate periods available for CLass B 'CS to transmit in. This is by design.

So to summarise, Class B 'CS' is not designed to work well in areas of high traffic, it is expendable in such situations.

what we need are class B 'SO' sets to arrive!

dave