Raymarine AIS

[sw]

Does anyone know how Raymarine E series handle AIS when there are no AIS
signals in the area? Does it just show "No AIS"? Since AIS nema data doesn't
xmit unless there is active signal, I assume that is the reason for the "No
AIS" message even though the receiver is hooked up and running? Does the the
display recover and show AIS data if it starts up without AIS data at
bootup?

Thanks

 

[sw]

Just so I understand, the E series will go from a "No AIS" warning on the
top right part of the screen to showing AIS targets once a target signal
comes in reception range?

Thanks for the help

 

[sw]

Thanks for the info. It's too bad in a way that you get the red X even
though the AIS receiver is hooked up and running. It strikes me as
confusing. My guess is that there will be improvements in the software down
the road.

 

[Tapio Sokura]

Thanks for the info. It's too bad in a way that you get the red X even
though the AIS receiver is hooked up and running. It strikes me as
confusing. My guess is that there will be improvements in the software down
the road.

The problem is that when no AIS transmitters are in range, the AIS
receiver isn't receiving anything and thus it doesn't output anything on
its serial port. This means that the device on the other end of the AIS
serial cable has no way of knowing whether there simply is no AIS
traffic within range or whether the cable is cut, or if the receiver is
malfunctioning. There is no "keepalive" so that the AIS receiver could
tell serial port listeners that it is still alive and kicking.

Tapio

 

[sw]

It would seem an easy task of the receiver designer to output data sentences
with just the header information when no transmitter is in range. Really
though, I would blame the Raymarine implementation. When you run AIS in
various PC charting software, you either see targets or not. No red X's, no
problems.

 

[Tapio Sokura]

It would seem an easy task of the receiver designer to output data sentences
with just the header information when no transmitter is in range. Really
though, I would blame the Raymarine implementation. When you run AIS in
various PC charting software, you either see targets or not. No red X's, no
problems.

I can see the logic in Raymarine software here, as there are two
possible scenarios: a) there is no AIS traffic in range or b) something
is broken with the AIS receiver setup. Situation a) is normal, but
situation b) needs to be looked at. There's no way an AIS serial stream
listener can deduce which one is the case, so to err on the side of
caution, an alarm is raised. Of course if you cry wolf too often you
might end up in trouble anyway..

Tapio

 

[sw]

We are using the Milltech AIS SR162, with the smart antenna splitter. The
splitter makes me nervous however. If it has a fault or blows it's fuse, the
VHF xmit will probably damage the AIS receiver. There is no indicator lamp
on the splitter so you really can't tell what's up....
I wonder what the signal loss is through the splitter?

 

[Peter Bennett]

The problem is that when no AIS transmitters are in range, the AIS
receiver isn't receiving anything and thus it doesn't output anything on
its serial port. This means that the device on the other end of the AIS
serial cable has no way of knowing whether there simply is no AIS
traffic within range or whether the cable is cut, or if the receiver is
malfunctioning. There is no "keepalive" so that the AIS receiver could
tell serial port listeners that it is still alive and kicking.

Tapio

I wonder if the commercial-grade AIS units do send a "keep alive"
message, and if there is a requirement for commercial systems to alarm
when no message is received from the AIS receiver for some time.

I've been beta-testing a charting program - initially, it not only
alarmed when it didn't receive AIS data, but it also DISABLED the AIS
input!! After some complaints, they changed things so it no longer
disabled the input, but still alarmed if data was not received for 10
sec., and required a manual click to acknowledge the alarm and remove
the alarm message box. The current version of the program has an
option to disable the alarm, so it is finally usable.

(The same program also disabled output to the autopilot if it didn't
get anything back from the autopilot. They removed that problem, but
I never did find out what they expected to get back from the
autopilot.)

One of the AIS-capable chart programs I have places a red line across
any vessel it hasn't heard from for some time (I forget the interval).
It doesn't sound alarms for this, so I consider this action
acceptable, and even desirable.

 

[sw]

I think two things should be required. There should be some indication if
the display unit/software has lost communication with the AIS talker,
whether there are currently targets or not. There should also be a simple
indication of lost signal from a particular target, such as the red line you
describe. This would provide the confidence in the system needed to make
navigation decisions.

 

[Geoff Schultz]

I installed a Milltech SR161 and an antenna splitter on BlueJacket just
before moving it from the Chesapeake to Ft. Lauderdale and I must say that
I was very happy with the performance. My VHF antenna is on top of my 60'
mast and most of the time I saw ships at 40 miles or less. On a less
frequent basis I would see ships at 40-60 miles away and I even saw a
cruise ship at 88 miles away. I was amazed and I realize that it must have
been some strange skip to hear a vessel so far away. In areas like
Norfolk, Charleston and Ft. Lauderdale I regularly had 50+ targets that I
was tracking.

The "no AIS" alarm was a real pain in fringe ares where a single ship's
signal would fade in and out and the alarm would keep going off. That has
to be fixed.

I was using this on a RayMarine C-80 and the biggest problem that I had was
with false "dangerous target" alarms. I have my MARPA/AIS alarm radius set
to 20 miles, such that if a target is within that radius an alarm will go
off. The problem is that all targets, even those at anchor or moored,
cause an alarm. I understand the logic behind this, but in my mind these
are false alarms. I also had problems with some targets generating
continuous alarms, causing me to shut off the AIS alarm. I reported this
to RayMarine and they say that a new version due out in Q1 of 2007 should
address these problems.


Despite the problems that I saw, I wouldn't be without this. MARPA on a
small sailboat underway can't begin to compare with the accuracy of AIS and
its fun to see information about targets such as names, size, type and
destination. I do look forward to getting a transponder when the prices
come down as I want the other vessels out there to see me as well as I see
them.

-- Geoff

 

[Bill Kearney]

The problem is that all targets, even those at anchor or moored,

cause an alarm. I understand the logic behind this, but in my mind these
are false alarms.

Well, if you're moving then their being anchored is still a problem.

I can also understand why, from a liability perspective, they'd still want
to issue an alarm for them.

But yeah, I'm with you on wishing the alarm function was a little smarter.
Or that the sound used for alarms was configurable instead of just one for
all of them.