Coast Guard warns of inaccurate AIS data

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That's only relevant if one relies on AIS data, and irrelevant if one doesn't have AIS. Nevertheless, thanks for the post for those who do. :flowers:
 
markpierce said:
That's only relevant if one relies on AIS data, and irrelevant if one doesn't have AIS. Nevertheless, thanks for the post for those who do. :flowers:
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When you are a slow boat caught in fog and trying to avoid a number of much faster commercial vessels including two vessels with several barges in tow, having accurate AIS data is VERY helpful in conjunction with radar.

I found myself in exactly that situation a couple years ago. Are those 4 targets a tug with three barges in tow, or are they 4 different vessels. AIS data can give you a good clue in a hurry.
 
I expect some commercial units don't update. The important
thing to me is that they are coming my way. Do I really need to know if there tow is 2,4 or six barges? I'm going to communicate via radio for the latest situation and passing arrangements. Just another perspective...
 
This has been a constant issue (especially towing vessels) keeping their user voyage info correct. However. It doesn’t really matter about voyage info if you know they are there, and (probably more importantly) if others around DONT have AIS, to give a complete picture of cpa, and when trying to avoid each other.
 
Not necessarily. ATB shows as one unit. The one I’m currently on does 12.5 knots light or loaded. Like a rocket ship.
 
Interestingly west coast port (iirc SFO) has a special designator. US sfo 123. Us country, sfo and numbers coorelating to facility, pier and berth! So much info. But it’s only good if it’s well know and universal.
 
Just today we passed two major refineries with associated LPG tanker, two large fuel barges and a handful of tugs. The tugs at anchor showed as underway, though with speeds less than 1 knot. One tug & barge combination simply said underway, while another showed pushing or towing alongside, the only accurate information given of the five tugs we saw. Yes, a quick call on VHF would eliminate any confusion, and I did consider asking one of them whether he was actually anchored or merely keeping station.
 
AIS data by design is NOT REAL TIME!!! With transmission periods of 1 to 6 minutes apart, the target(s) can move a long way between updates.
 
High Wire said:
AIS data by design is NOT REAL TIME!!! With transmission periods of 1 to 6 minutes apart, the target(s) can move a long way between updates.
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Yep, following some folks on a night trip revealed that. Seemed more like 30 seconds, but I was regularly 'catching up' to the AIS marker for the boat in front of me. Radar and visual revealed otherwise. Likewise for all the other boat traffic and nav markers out there.

I could understand where in reduced visibility this would be a problem. Esp with regard to towing setups.
 
Class A AIS (Commercial shipping) reports position every 2-10 seconds depending on speed - every 3 minutes if moored or at less than 3kts.

Class B-CS AIS (Recreational boats normally use this type) report position every 30 seconds, or every 3 minutes if moored or at less than 2kts.
 
A tug towing won't have the actual length of the tow, only the size of the tug. Use AIS to get a name then use the VHF. Like you said, you're not going fast so things aren't happening quickly.

If you think fleet boats are going to change AIS everytime they move, you've lost your mind. They stop, go and change barges all the time.
 
To me, the big advantage of AIS is getting the name of the vessel. Then you can hail them and get the details if necessary.
 
One thing I get out of reading this thread is the need to make sure I do not set my receive AIS to delete targets sooner than 3 minutes because a vessel could be sitting DIW in front of me transmitting only every three minutes. Granted, I should have a lookout posted and radar in use in low visibility to avoid collision, but I'm just sayin'.....
 
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