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Old 11 April 2019, 05:36   #1
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"Online AIS" users beware!

Just a note for those who use/intend to use third party AIS data from the internet as a safety aid at sea.

I have noticed that the reported position of a vessel can change as the zoom level is altered. Clearly the idea of using online data in this way has obvious flaws such as coverage, network access, network delays etc. This is the first time that I have seen something as glaringly dangerous - a single vessel being reported in more than one location. IMO avoid!!
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Old 11 April 2019, 07:38   #2
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I think the warning they give not to use the online data for safety because of the up to 10 minute feed delay could play a major part in not using it for an actual navigation aid!
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Old 11 April 2019, 07:58   #3
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Quote:
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I think the warning they give not to use the online data for safety because of the up to 10 minute feed delay could play a major part in not using it for an actual navigation aid!


Yup thereís many a time that marine traffic has had us out at sea when weíve been back in the harbour & vice-versa. Sometimes its hours before it updates, not just minutes.
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Old 11 April 2019, 08:15   #4
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I've never tried one but I have been tempted to get one of those quark ais receivers there's some on ebay with nmea and WiFi for not a terrible amount I guess using one of those connected to your phone would be much more sensible even if the range is only a few miles. It's better than looking at a ship at anchor on the online map the looking up to see it heading for you at about 20 kts
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Old 11 April 2019, 08:34   #5
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I must be missing something cos i cant see the usefulness of ais over other nav aids. Apart from the novelty value what does it tell you that radar chart plotter and mk1 eyeball cant?
Ok if your a big ship moving relatively slowly in a busy waterway but a small fast boat that would usualy navigate at 90 degrees to a tss or outside the main chanel what is the benefit of it.
I've never used it on a small boat but have looked for the position of the commercial vessel I've been sat on only to see it shows our position several hours ago.
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Old 11 April 2019, 11:52   #6
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I must be missing something cos i cant see the usefulness of ais over other nav aids. Apart from the novelty value what does it tell you that radar chart plotter and mk1 eyeball cant?.


Well not everyone has radar so it may be a cheaper alternative that is easier to install. Thereís also more skill to reading a radar plot (and at speed that may be even harder). Iím not sure if Radar and the right for example predicts the future position of the target.

Iím not a user though - on a 4m 20 knot boat if the eyeball isnít sufficient to tell if itís a good idea to be there Iím pretty sure itís not!
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Old 11 April 2019, 14:26   #7
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Name of the vessel, MMSI no.
You may or may not consider that useful
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Old 11 April 2019, 15:22   #8
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So I didn't mean to start an AIS debate - rather to point out how a vessels position as charted on the online Apps can vary dramatically depending on the zoom level you use. I spotted one today travelling north, zoomed in for a closer look and it was steaming south a half a mile away. Zoomed out and it was back in the other position steaming north. Useless/dangerous.

Seeing as we've drifted I'll mention that AIS has all sorts of wee tricks up it's sleeve. Collision alarm, CPA, vessel activity, vessel speed, name, etc. The ability to make a quick VHF call to a vessel displaying AIS position has to be good - even just having the name is a plus - being able to ring an alarm on their bridge is great. In the event of a Mayday, AIS can be used by the rescue services to pinpoint your position. The list goes on, and I'm sure someone will....

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Old 11 April 2019, 16:43   #9
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Ended up in dense fog on two North Channel crossings. (I think trying to avoid boating in rough weather predisposes you to a higher risk of encountering fog that accompanies light winds) . AIS (like everything else) is not a panacea but it gives you reasonable confidence you're not going to be confronted by the 30 foot high bow of a P&O ferry looming out the fog twenty yards away and that was my biggest worry. If it's "Class A" chances are it's not monitoring "Class B" transmissions to reduce "clutter" and it's not going to take any evasive action but from your own point of view, at least you know it's out there, where it is, name, speed, heading, bearing and where & when it's going to collide with you if you don't do something about it. One of these things that's simple to fit and cheap enough to be worth giving a try. Wouldn't be without it now.
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Old 11 April 2019, 17:57   #10
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Moderately interesting wee article in MBY this month about the new AIS B+ transponders. As previously mentioned in various threads on here, I think AIS is probably most useful for small craft as a tool to let you know where the big boys are rather than them knowing where you are, but it's interesting to note how infrequently AIS B transceivers broadcast. At 25 knots you've done more than 400 yards in 30 secs.

Not a criticism mind, if I was doing passages in open water I'd definitely look into AIS. Just thought it was interesting thats all.
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