Missing AIS targets

[tonyburn]

I have recently installed AIS, EasyAIS (Channel A & B) through an EasySplit linked to a Garmin 4008 chartplotter, but notice that sometimes the AIS targets (commercial vessels) do not always show even within 1/2 mile. Most of the time targets are showing it is just these ocassional ones.
For ref my sailing area is the Solent so there are generally plenty of AIS objects it is just these missing ones that concern me. Has anyone any ideas / suggestions

 

[mikejames]

If they are not changing course then they may only be transmitting every 2 minutes. At 15 knots there is your half a mile.
Actually I think Southampton VTS is commanding a lower update rate than this to allow everybody some chance of getting through ....


I think that typically its about once every 4 minutes or so the vessels update in the Solent.


I dont think the Garmin chartplotter predicts the positions of AIS targets from their last known speed. My GPSMAP450S doesnt.

I tried predicting vessel positions while writing code for a commercial program for which I wrote the AIS plotting bit, and I kept on getting the Red Jets ramming Fawley when they were moving at 38 knots and turning hard round Calshot, when I left prediction on.

 

[noss41]

Can anyone explain the rational of he AIS targets? Is green cargo? If so what is blue and what is yellow? Red is too close for comfort

 

[Leighb]

Perhaps the colour scheme depends on which AIS and Plotter you have?

I have NASA AIS and STH plotter and all targets are just black triangles.

With this I only get limited info on the target, but then do you really need to know the destination, or type of vessel or its status - Anchored - underway etc.

These are all input by ships officer and are often wrong/out of date anyway. Not unusual to see and anchored ship doing 20 knots or destination Felixstowe when it is clearly going the other way :grin:

 

[Pete7]

We were followed from Cowes to the forts on Sunday afternoon by a small coaster. Not a sqeak from the AIS unlike the large container ship going the other way which showed up miles away. I assumed he either didn't have AIS or it wasn't switched on.

The Garmin 555 series will plot a course for targets but only if you have entered your destination into the plotter. We watched the plot of a fast Red Jet Ferry change dramatically as he rounded the west Brambles bouy for Cowes on Saturday afternoon. It also gave us the time to impact which was less than 60 seconds so we briefly altered our course to avoid him.

Pete

 

[daibachsail]

Missing Targets

We have noticed on recent cross channel trips that sometimes there are very few showing while at otheres there are large numbers eg 20. This is with same range and target settings and in a short period of time when they could not have moved far. This is with EasyAIS interfaced to Standard Horizon running C-Map.
There apears to be little logic but it is worrying as previously in poor vis we had assumed all were showing!! and were more relaxed than usual with that knowledge.
Any ideas about these phantoms?

 

[Captn D]

Regarding colours of targets. This appears to be plotter dependent. One just has to observe a number of targets and work out what each colour represents!

 

[bendyone]

Have a look here

http://www.shipais.com/index.php?map=uk

 

[fireball]

or http://aprs.fi/ - integrated into Google Maps....

 

[sailorman]

is ais really of any use in the solent

 

[alexrunic]

I ve been told that some of the ships do not have the ais switched on because of industrial espionage. I too have noticed not all ships seem to show up, this would be a logical reason.

 

[fireball]

AIS of use in the solent - surprisingly yes ...

it allows us to see what is coming round the Nab and know if it is going onto Southampton or into Portsmouth - and also what is coming out of Southampton & Portsmouth ... so we know if we need to make a swift crossing of the channel near the forts or if we can take a more leisurely route...

As for collision avoidance - it you haven't spotted it then you should be sailingwith able bodied ppl!

 

[Leighb]

I ve been told that some of the ships do not have the ais switched on because of industrial espionage. I too have noticed not all ships seem to show up, this would be a logical reason.

As AIS is mandatory for all vessels over 300GRT this would be a flagrant breach of International Regulations would it not? It seems unlikely that they would only be required to have it fitted but not use it?