AIS, RADAR and CPA

[PMC]

Last week we pulled into the lee of an island to anchor. On the port beam, 0.2 miles away on the radar was target, which was an vessel at anchor showing the proper lights. There was also an AIS-generated triangular target only .05 miles away are the port beam. But there was no moon to see anything and there were no lights from the vessel. Problem was it was the AIS transponder signal from the boat on are starboard beam!

I sure would not have want to rely on an AIS-generated CPA based on a position that was 1/4 mile off the actual position of the vessel!

Anybody else run into this situation before?

[anchorman]

Can't say that I have personally, but I never use AIS as a plotting tool unless it's associated with an actual radar target - AIS helps identify a target, but not useful in determining if one is there are not - that's what the radar, and more importantly the windows are for. Check your offsets on both pieces of equipment to make sure they're both set-up correctly. You might have just found out how this is more apparent using radar on 1.5 mile scale versus 12 mile - where the error may not be so evident.

[UnRepKing]

On many occasions I have noticed problems with other Vessels AIS. Ship is inbound in Thimble Shoal Channel but its AIS symbol is point back towards Cape Henry, ship is anchored and its AIS symbol is sitting over the water 300 yards aways from the ship, etc..... When comming in and out of port the Pilot will normally alert ships if something is wrong with thier AIS, out at sea I will also contact ships to tell them their is a problem, I will also ask them to read back my own AIS datat to me.

I would never reccomend using AIS data for collision avoidance or making maneuvering decisious, always stick with you physical radar return of a big chunk of metal sitting on water. I always turns off the AIS overlay on the RADAR also...to much information, I have my AIS receiver and ECDIS right thei next to the RADAR.

[PMC]

I was on this vessel for a 3800 mile delivery. The AIS target at anchor was literally the only vessel over 40 feet long that I saw on the entire crossing. THis was my only experience with the AIS tie-in on radar.

[mtskier]

I have regularly seen the AIS symbol and the radar return (target isn't PC I'm told!) be separated by a measurable distance. Don't know if it is a set up issue or an error, or both. I keep the AIS overlay turned off on the radar as well, though find it handy on the ECDIS. My favorite is the slowly rotating AIS symbol.

[ollie]

I don't let the AIS anywhere near my radar. Turn that crap off. Garbage in / garbage out, right? But I'm like mtskier in that I find it handy on the ECDIS.

[dredgeboater]

I have seen that issue on Sperry Visionmaster FT radars with AIS integration. Once was improper offset for RADAR antenna position and the other time was gyro error.