[PUP] AIS

[John Marshall]

Stan,
    Interesting comment on the Class B "degrading" out of the system. If I 
recall, the Class B units transmit far less frequently, and at lower power, 
so if there are many Class A's in the area, then all the time slots may be 
taken by the A's. I think that's what you are referring to. In that sense, 
it won't prevent an A from getting its signal out.

However, even if that happens, the guy with the B will still see everything, 
he just might not get his own 'voice' out.

My Furuno FA150 Class A unit denotes Class A versus B units in a target's 
data field. It would be easy to have a chart plotter program filter the B's 
out.

That said, I haven't seen any filtering software options on Furuno, Nobeltec 
or Coastal Explorer yet. Not sure what software the big guys use and whether 
its different. But I'm assuming its a given that if the screens get 
cluttered, the big guys will filter things out somehow.

Lastly, not everyone is willing to pay the huge premium for a Class A 
transceiver, or even the 2x for a Class B transceiver, when a simple AIS 
receiver gives you 90% of the benefits. (At least, given that your strategy 
when dealing with large ships is to take responsibility for avoiding them, 
all on your own, regardless of right of way rules.) But if you want to 
routinely run in the shipping lanes under VTS control with the big guys, 
then buy an A).

John


----- Original Message ----- 
From: "Stan" <crossroadsn50 at yahoo.com>
To: "Passagemaking Under Power List" 
<passagemaking-under-power at lists.samurai.com>
Sent: Sunday, October 26, 2008 9:33 AM
Subject: Re: [PUP] AIS


>I installed a Class B AIS on my boat at the beginning of this past
> summer's cruising season in the PNW. I also added an ARPA board to my
> Simrad radar. I could not be happier with both of these tools. They
> serve similar functions but each have advantages over the other. The
> AIS literally allows us to "see" around  land masses which in the PNW
> with its many narrow passes, heavy cargo, tug, cruise ship and ferry
> traffic is extremely helpful. The ARPA helps us track non-AIS targets
> which is invaluable.
>
> For those that are concerned that too many pleasure boat AIS
> transmitters are a problem, you should know that the Class B system is
> intentionally designed to automatically degrade out of the system when
> it becomes overly crowded. There is also the concern that large ships
> being unconcerned with the pleasure boat crowd will just filter us out.
> This may eventually happen, but in my mind anything that makes me, or
> may make me, more visible to other traffic is a good thing. I also
> figure that if I have a concern, I can call up the vessel I'm concerned
> about and ask if they see my AIS transmission, alerting them to my
> presence and prompting them to turn off whatever filters they have so
> that they can get a bearing on me. I had cause to do this in the
> Johnstone Strait this summer and the cruise ship I was hailing
> eventually made adjustments to their AIS to confirm that I was indeed
> showing up on their screen.
>
> Whether you get, a Class A system or Class B system (bought mine in
> Canada, because the FCC had not yet approved it at the time, and paid
> about 30% of the cost of the Class A system), I think that the AIS
> transceiver is a wonderful enhancement to boating safety and peace of 
> mind.
>
> Stan Heirshberg
> CrossRoads N50
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