Good question. On Long Island Sound there is a constant parade of BIG
shipping much of it tug & tow traffic. Sailboats are often in conflict with
them. I have to admit it's difficult to judge speed and distance when trying
to cross in front of or decide to wait and pass behind a tug with two
barges. AIS will put a target for this traffic on the electronic chart with
speed, bearing, name of vessel and about 15 other pieces of information. In
addition, it will show these targets as far away as you can receive VHF
signals. One reported test with the receiver on a high point of land along
the coast picked up vessels 80 nm away which is better than my radar. AIS
does not replace radar as lots of ships are not required to transmit an AIS
signal such as small fishing vessels and anything recreational. Software
like "Coastal Explorer" also alarms if a target is on collision course and
gives closes point of approach info. If you have to call a ship on the radio
you can do so by name instead of, "Freighter on my port bow".

>From what I understand the available AIS Transmitters cost around $3000. The
signal is sent out on two different VHF channels alternately a second apart.
The reason the AIS unit I purchased is only $225 is because the designer
kept it simple with only one frequency receiving data. This means you only
get an update every two seconds, (which is just fine for a sailboat
traveling at 6 knots).

When I sailed to Bermuda a few years ago I was on watch during the evening
and kept visually scanning the forward horizon as a big freighter drove
right up behind us to within less than a half mile before making a 45 degree
change in course and continuing on over the horizon. AIS may have been
helpful in seeing his target on the chart well before I went on watch. This
would have been even before radar could pick him up.
The AIS receiver I purchased is the least expensive unit on the market at
this time. There is another receive only unit made in China for $595us via
bank transfer only. Both units have had good performance comments by the few
people who took a chance and bought them. I would rather risk $225 for new
technology than the $595. In my opinion, this device is worth about $50. All
it consists of is half of a VHF radio receiver, (audio portion is not
needed) and a circuit to turn the raw signal into a NMEA string. The case is
a black box with serial output, power and antenna BNC plug. That's it!

Finally and most important - we can really do without all this electronic
stuff, after all, sailors cruised the oceans with just the stars, paper
charts and pencil for centuries. I'm a gadgets type person and get a kick
out of all these new devices. Maybe this is the core reason I bought the AIS
unit.

Richard Cassano
S/V Gray Eagle, Tashiba 40


> -----Original Message-----
> From: Bruce [mailto:bcp # pappalini.com]
> Sent: Friday, June 03, 2005 11:43 AM
> To: Baba, Panda and Tashiba List
> Subject: [baba] AIS receiver (was Sea Tech steps on their necktie yet
> again)
> Importance: High
>
> Richard,
> Can I ask why you bought an AIS receiver? And why this one?
> I wonder what a transmitter would cost?!?
> --Bruce



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Received on Fri Jun 03 12:23:04 2005