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Old 11 April 2019, 06:36   #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, 08:38   #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, 08:58   #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, 09:15   #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, 09:34   #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, 12:52   #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, 15:26   #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, 16:22   #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, 17:43   #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, 18:57   #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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Old 12 April 2019, 14:39   #11
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AIS ....Aids Insecurity Sufferers???
......Maybe not.....
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Old 13 April 2019, 03:37   #12
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Not the same as AIS I know but I run an app on my iPhone called Boat Beacon. If you are meeting up with friends on the water and you are all running the app on your phones
it shows your locations boat names etc.

My wife finds it useful too as she knows where I am at sea. If you use the app and you have a mms I numer you can share your position with other full AIS users. (Which I did when I had a sailing boat)
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Old 13 April 2019, 04:28   #13
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Not the same as AIS I know but I run an app on my iPhone called Boat Beacon. If you are meeting up with friends on the water and you are all running the app on your phones
it shows your locations boat names etc.

My wife finds it useful too as she knows where I am at sea. If you use the app and you have a mms I numer you can share your position with other full AIS users. (Which I did when I had a sailing boat)
BoatBeacon is using AIS data though... so you'd want to know if it shows inaccurate locations.

@Willk - screenshot or more info? Wondering why it does it - and so fancied a wee nosey at a data log... #geek_alert
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Old 13 April 2019, 04:42   #14
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As a footnote - AIS is of huge importance to any boat with a MOB. In ISAF/RORC special regs for instance lifejackets will now have an AIS beacon signal that triggers when the lifejacket inflates. This MOB signal is seen immediately by any AIS receiver in range - unlike an EPIRB which can take up to an hour to pinpoint (and any vessel nearby is very unlikely to be able to receive an EPIRB emergency signal). I am of the opinion that AIS is one of the most innovative safety inventions in recent times.
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Old 13 April 2019, 12:03   #15
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As a footnote - AIS is of huge importance to any boat with a MOB. In ISAF/RORC special regs for instance lifejackets will now have an AIS beacon signal that triggers when the lifejacket inflates. This MOB signal is seen immediately by any AIS receiver in range - unlike an EPIRB which can take up to an hour to pinpoint (and any vessel nearby is very unlikely to be able to receive an EPIRB emergency signal). I am of the opinion that AIS is one of the most innovative safety inventions in recent times.


I think you may mean huge importance to serious racing yachts if the crew happen to be wearing a LJ at the time they go overboard...
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Old 14 April 2019, 16:50   #16
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@Willk - screenshot or more info? Wondering why it does it - and so fancied a wee nosey at a data log... #geek_alert
So, I was going to ignore this in case Poly butted in and went all OCD on it - but I'm sure you'll be more sympathetic...

I don't have any screenshots. I retain CCTV of Reportable Incidents, but not Quirks of the Internet. That said, if you select a vessel on Marine Traffic that is running over (let's say) 20 kts - mark it by a waypoint or nearby geographical feature and then zoom in and out a few layers. You'll be surprised to find it jump back and forwards. Or north and south, if it has taken a recent turn.
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Old 15 April 2019, 02:55   #17
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In the attached PDF I randomly chose two fishing boats - Fladda Maid (FM) and Stella Maris (SM).

The top two screenshots are at the same zoom scale and you can see the course, speed and update time of the two vessels.

I then zoomed in and did another two screenshots. FM has increased speed slightly and has changed direction. The position was updated three minutes earlier which is the same as the previous zoomed out screenshot.

SM is doing the same speed and direction but the update was carried out two minutes earlier.

To capture the screenshots, change the zoom and re-capture the screenshots took 30 seconds.

For FM, even though it's reasonable to assume both screenshots are based on the same position update time, the course and speed are different.

For SM, whilst the course and speed are the same, the position update only happened two minutes previously rather than three.

It's 'interesting' in a geeky way that simply zooming in and out changes the information in a slightly illogical way.

I'm off to get a life now.
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File Type: pdf AIS.pdf (51.5 KB, 21 views)
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Old 15 April 2019, 07:40   #18
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I think you may mean huge importance to serious racing yachts if the crew happen to be wearing a LJ at the time they go overboard...
Not just racing yachts - most crews on different boats wear lifejackets today - and increasingly many cruising yachts / motor boats have simple Raymarine type MOB systems installed. The point is anyone with an AIS receiver (who is in proximity of an MOB wearing this system) can see the position of the MOB on their GPS. If you can afford to install this equipment why wouldn't you? If a single hander fell out a rib at speed (and was not able to get back to the boat) you have an outside chance of being spotted by someone with AIS if there are other vessels in proximity. The more sophisticated systems will also trigger an alarm to Solent Coastguard etc
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Old 15 April 2019, 10:42   #19
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Not just racing yachts - most crews on different boats wear lifejackets today
we must be circulating in different boating worlds! Am I wrong on thinking that even although ISAF/RORC are insisting this tech is fitted to the LJ they don't actually require the LJ to be worn?

Quote:
The point is anyone with an AIS receiver (who is in proximity of an MOB wearing this system)
i've highlighted the relevant bit in bold. My point which I am sure you are getting, but choosing to ignore, is that AIS is not "of huge importance to any boat with a MOB" but is a useful tool if you happen to have the AIS enabled personal locators on your LJ's and one goes overboard. Thats an argument for fitting the AIS locators to your LJ and logically to fitting an AIS receiver on your own boat - its not a great argument for me (or anyone else) fitting a receiver in case I'm close to MOB.
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Old 15 April 2019, 13:24   #20
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An interesting bit of thread creep which has been discussed before.

PLB vs AIS MOB

There is a combined unit on the market designed by that well known maritime nation - Austria.

https://seaangel.at/index.php?route=common/page&id=2906
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