First Time with AIS.

[DJE]

I Installed OpenCPN and took a feed from the main Furuno GPS via a serial to USB converter to the laptop earlier this season. But just before crossing the channel a couple of weeks ago I managed to lash up a pushpit antenna mount that Blue Peter would be proud of, bought a Bellfield USB AIS receiver and installed that on the laptop, connected a cheap VHF antenna, and I had a working AIS system for the first time on my own boat.

Generally very pleased with it but the list of improvements includes a proper 12V power lead from the laptop to avoid the need to use the inverter, a better antenna mount a bit higher up, and a stand-alone USB GPS dongle to replace the serial to USB converter from the Furuno GPS. First impressions are that the graphical display of relative tracks and closest point of approach in OpenCPN is excellent and that the weak link is definitely the Windows computer which will work happily for hours than suddenly decide that can't see COM3 or COM6 for some reason.

But the AIS receiver seems to take a very long time to aquire targets that I can clearly see a few miles away, and sometimes it never recieves data like the ships name and dimensions. Important stuff like position, course, speed, and MMSI seems to come up relatively quickly though. There is something in the AIS reciever manual about setting it up to scan more than one channel and I would be grateful for any advice on this. (I think I need to double check all my antenna wiring connections though.)

But it was worth its weight in gold in fog in the west-bound lane on the way back last Friday!

 

[BrianH]

But the AIS receiver seems to take a very long time to aquire targets that I can clearly see a few miles away, and sometimes it never recieves data like the ships name and dimensions. Important stuff like position, course, speed, and MMSI seems to come up relatively quickly though. There is something in the AIS reciever manual about setting it up to scan more than one channel and I would be grateful for any advice on this. (I think I need to double check all my antenna wiring connections though.)

Data is sent in two transmissions - dynamic and static - the former with "important stuff" is dependant on speed but only a matter of seconds repetition while the latter, with such as name of ship, etc., every six minutes.

Most cheaper AIS receivers (don't know about your Bellfield but others, such as the NASA) are only single channel reception at any one time and alternate that channel after receiving a target report. As the senders alternate too it can be a while before they synchronise. Mine, an old, cheapo Taiwan one, can take up to 20 minutes to get the static data for an acquired target. No big deal but nice to have the ship's name to shout at on VHF channel 16 if heading straight for you.

Always better to get a simultaneous, parallel, two-channel receiver - all the transponder systems incorporate such receivers.

 

[nigelmercier]

... the weak link is definitely the Windows computer which will work happily for hours than suddenly decide that can't see COM3 or COM6 for some reason...

But the AIS receiver seems to take a very long time to aquire targets that I can clearly see a few miles away, and sometimes it never recieves data like the ships name and dimensions...

The COM port problem will go away with a decent USB adaptor:
http://www.amazon.co.uk/exec/obidos/ASIN/B004ZMYTYC/dolcetto-21
http://www.amazon.co.uk/exec/obidos/ASIN/B0055CRAF6/dolcetto-21

Try the dual channel setting.

 

[rogerthebodger]

Last time I was on my boat I also setup OpenCPN and was very pleased with the result.

My setup is GPS USB dongle, NASA AIS with RS232/USB converter. I also connected my SIMRAD old IS11 instruments picking the output directly then through RS232/USB.

All inputs go through NavMonpc and then passed to OpenCPN using virtual ports and seems to work very well.

My AIS aerial is mounted on my taga about 2 meters above deck.

When moored in Durban Harbour I was picking up to 66 targets, most moored, but some out at sea up to 14 miles away beyond a harbour headland which was quite pleasing.

Of the targets identified about 50% had all the details after about 15 minutes of operation, which I don't think was too bad.

The data from the SIMRAD was shown on the NavMonpc and on the OpenCpn dashboard plugin without too much trouble.

I was running my laptop from 12vdc power supply and also displayed on both the laptop and on my 2 TV's which have VGA input, TV's also direct from 12VDC supply.

I plan to connect a USB mini screen to the laptop and mount in a custom stainless weather proof box at the outside steering station. I also am going to get a fanless 12VDC pc like this http://www.mini-box.com/M350-Intel-DN2800MT#SYS-M350-Intel-DN2800MT-configurator to replace the laptop.

Keyboard and mouse are cordless to I could use the mouse at the outside steering station if needed.

The next 2 development are to connect SSB to receive weather fax and to complete the build of a weather satellite receiver to all display of satellite weather pictures.

One trip I did from Durban to Cape Town on another yacht which had the Raymarine chart plotter and AIS did not display any secondary AIS info but I did not have time to investigate so was quite pleased with my NASA unit in that context.

 

[tudorsailor]

A lot of commercial ships do not transmit their name and destination so it is not something to do with your setup. Having their MMSI number is a waste of time as I have not succeeded in getting a responce from an MMSI call

I use the Globalsat GPS receiver receiver

TudorSailor

 

[prv]

A lot of commercial ships do not transmit their name and destination so it is not something to do with your setup.

Really?

Destination I don't know about, as my old plotter didn't display it - and as a manually-entered field anyway I can believe some would not bother. But I've more or less always had a name for each target within a few minutes of seeing it.

Perhaps you're missing some of the static transmissions?

Pete

 

[tudorsailor]

Really?

Destination I don't know about, as my old plotter didn't display it - and as a manually-entered field anyway I can believe some would not bother. But I've more or less always had a name for each target within a few minutes of seeing it.

Perhaps you're missing some of the static transmissions?

Pete

My sailing is around Italy and Croatia. Some ships names do come up - especially big MOBOs, but many commercial ships such as freighters do not have a name displayed. I guess I have to check this by looking at someone else's AIS when moored up and comparing notes. However I have heard the coastguard calling ships by their MMSI so I assumed that they cannot see the name either

TS

 

[BrianH]

My sailing is around Italy and Croatia. Some ships names do come up - especially big MOBOs, but many commercial ships such as freighters do not have a name displayed. I guess I have to check this by looking at someone else's AIS when moored up and comparing notes. However I have heard the coastguard calling ships by their MMSI so I assumed that they cannot see the name either

I have been using AIS through the entire Adriatic for six years now and can not recollect not having the name attached to a Class A target - which all commercial ships are - given enough time for the static sentences to synchronise in my receiver; a dual-channel but single, alternating reception that consistently misses the active channel. I have however, often observed Croatian ferries with no AIS signal at all being transmitted.

Class B targets are correctly displayed but I never get any static data displayed as my receiver was produced before the Class B protocols were finally formalised.

Whilst the name and dimensions are always present, other Class A static data is often not manually updated, so that a ship clearly underway can be still shown as "Moored", for example.

 

[tudorsailor]

Hmm, Now you got me thinking. I have a Comar multi. I wonder if it takes time for the name to show. I will need to check. Certainly heading and speed seem to appear as soon as the target shows.

Fishing boats never seem to transmit. Is this your experience too?

TS

 

[MoodySabre]

I have the same Marine Gadgets USB AIS dongle. It doesn't usually show the name.

The default setting is Channel B. it is possible to change this if your chart plotter has the facility or if you have a terminal program. Instructions in the manual.

I use a Globalsat USB GPS and it is very good

 

[BrianH]

Hmm, Now you got me thinking. I have a Comar multi. I wonder if it takes time for the name to show. I will need to check. Certainly heading and speed seem to appear as soon as the target shows.

The dynamic data transmission are what initiates the target in the AIS list and will, of course, display immediately and as the repetition rate is in the order of every few seconds will be constantly updated. The associated static data transmission, on the other hand, is sent every six minutes and will be added to the target list data for display. As transmission alternates between the two VHF channels it can be missed (especially by single channel receivers that may be listening on the other channel) and have to wait for another six minutes for another chance to receive it. Missing a transmission by not being channel synchronised is no problem for the frequently transmitted dynamic data - only a few seconds delay will be the result.

Fishing boats never seem to transmit. Is this your experience too?

Indeed yes, they are not legally obliged to transmit AIS signals, along with such classes as warships, on the grounds that very often their positions need to be kept from their competitors. In the northern Adriatic some do transmit Class B signals - no doubt turned off when they are anywhere near their favourite fishing grounds.

 

[prv]

I wonder if it takes time for the name to show. I will need to check. Certainly heading and speed seem to appear as soon as the target shows.

Yes, that's entirely normal.

The "dynamic" data, things that are always changing like position, heading, and speed, are broadcast every few seconds. These transmissions are identified only by MMSI, so when your receiver picks them up first (which it almost always will) it can only label the target with MMSI, not name. Some time in the next six minutes, the ship will broadcast a "static" message, with the things that do not change such as the size of the ship, name, destination, etc. A parallel dual-channel receiver should get this straight away, and update the target to have a name instead of a number. A cheapo receiver that switches between channels may miss one or more messages through being on the wrong channel at the time, so could take much longer to catch the static packet and show the name. But that's the fault of the receiver, not the ships.

Pete

 

[prv]

The default setting is Channel B. it is possible to change this if your chart plotter has the facility or if you have a terminal program. Instructions in the manual.

So it can only ever listen to one or other of the channels? Seems pretty poor to me, deliberately missing half of the transmissions.

Pete

 

[MoodySabre]

The manual says that ships transmit on A and B so you should get all the information on one channel. If you set it to switch between A and B then you could miss several cycles if it switched just before a transmission. You can set the switch pattern to every 10sec or longer up to 50secs.

Mine runs on the default and seems fine.