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Old 05-09-2016, 10:02   #256
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Re: AIS, Receiver or Transmitter

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Originally Posted by nigel1 View Post
. . . I would still use compass and eyeball though to confirm what the AIS is telling me, it's not in me to base avoidance action alone on the AIS. . .

Then we agree completely.

In the most intense collision avoidance situations, I have a crewman on deck doing a careful visual watch with a HBC. Confirming what radar and AIS are telling me at the nav table.

I've never seen a case where AIS gave wrong information, but we can imagine it could happen, and I don't find it acceptable to risk steering right into a collision based solely on data from only one source. I check AIS against radar, too. Radar doesn't lie. I check the chart plotter against radar, too.


And for all of that, with every passing year of accumulated experience, my fear of collisions does not reduce. It's a low probability of a terrible consequence, and we all sail "under God", as the Russians say, meaning we are saved probably much more often by luck, than by our own skill. It's why I am constantly trying to improve my skills and procedures.
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Old 05-09-2016, 10:37   #257
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Re: AIS, Receiver or Transmitter

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Originally Posted by Dockhead View Post

I've never seen a case where AIS gave wrong information, but we can imagine it could happen, and I don't find it acceptable to risk steering right into a collision based solely on data from only one source. I check AIS against radar, too. Radar doesn't lie. I check the chart plotter against radar, too.

Have seen on quite a few occasions (at work), "ghost" targets on the AIS.
One was a ship showing up in the middle of Aberdeen harbour turning basin, and her true target was in the anchorage about 2 miles away.
Another was a fishing vessel, AIS target about 3 miles east of Peterhead, but a double check on the AIS also showed her true position as in the harbour, and a third occasion was in the Baltic where the AIS gave a SAR target on a steady bearing. We eventually found the true target tucked up and stationary in Visby harbour.

And the most worrying one was a target of my own tug, constantly appearing on the AIS 1 mile on the stbd quarter. Had to get the Furuno tech in for that one, who confirmed it was not a one off problem, and it was fixed with a software update.
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Old 05-09-2016, 10:57   #258
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Re: AIS, Receiver or Transmitter

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Originally Posted by Dockhead View Post
I've never seen a case where AIS gave wrong information, but we can imagine it could happen, and I don't find it acceptable to risk steering right into a collision based solely on data from only one source. I check AIS against radar, too. Radar doesn't lie. I check the chart plotter against radar, too.
I've seen AIS position errors before. Once, a ship that passed us by a mile to the north of us was reporting their AIS position as being about a mile to the south. But this was back in 2006 and as it turned out probably due to a known configuration error where their GPS lat/lon was "adjusted" to make their chart display correctly. This adjusted lat/lon was then fed to the AIS transponder. There were bulletins from the USCG that described the problem, and I haven't seen errors like that in a long time.

I was visiting the San Francisco Vessel Traffic Service site a few years ago and the officer there was telling me about an incident where several moored ships apparently started drifting across the bay all at once. The problem was that their GPS receivers were confused by a GPS satellite (WAAS?) switchover. Most receivers handled the change correctly, but these were older units that needed to be manually reconfigured (or something like that.) VTS also had the ships on radar.

My point is that although they are extremely rare, position errors can happen. Which is why most of us apparently still use our radar and compass to double-check this critical information.
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Old 05-09-2016, 11:18   #259
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Re: AIS, Receiver or Transmitter

Wow! can't we settle this? The $400 free standing Matsutec TX/RX AIs is not a large expense for the added information and safety. Receive only makes you a stealth target. Not a substitute for radar, but a whooping advantage. Little noted is that it also puts your track in the internet. We get plots of our location from friends and family, rather than the other way around. My only gripe is people leaving them turned on while in the marinas - you can get some crazy collision alarms while not seeing the real stuff. I would not, now that it is available, go as far as the Bahamas or off shore at night without it.
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Old 05-09-2016, 12:54   #260
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Re: AIS, Receiver or Transmitter

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Originally Posted by El Pinguino View Post
Can I tell you if she shall pass 1 mile or 1.1 miles ahead? No...
Can I tell if risk of collision exists and if the ship shall be passing closer than I am comfortable with... yes.
People have been doing it since Noah was a deck boy.
Absolute BULL! Noah was never a deck boy. builder to capt, LOL
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Old 05-09-2016, 13:18   #261
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Re: AIS, Receiver or Transmitter

I was taught in Fleetwood marine college about RADAR assisted collisions. I didnt believe it...

Then I did a 300 mile offshore and watched 2 tankers scrape off other.

Unbelievable! but my tutors experience and knowledge went up in my estimation 100%.
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Old 05-09-2016, 15:10   #262
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Re: AIS, Receiver or Transmitter

He was a farmer. Use your Internet.

When the flood came, he escaped to the roof of his shed together with whatever food he could grab: goats, hens, etc.

Later the story got blown out of proportion by Christians: the floating shed became an ark and the goats became elephants.

There is also a claim that Noah had some early forms of radar or AIS - back then known as 'doves'.

Too bad some modern day sailors insist on sailing as if Noah story was anything but a story.

Cheers,
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Old 05-09-2016, 16:45   #263
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Re: AIS, Receiver or Transmitter

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Originally Posted by barnakiel View Post
He was a farmer. Use your Internet.

When the flood came, he escaped to the roof of his shed together with whatever food he could grab: goats, hens, etc.

Later the story got blown out of proportion by Christians: the floating shed became an ark and the goats became elephants.

There is also a claim that Noah had some early forms of radar or AIS - back then known as 'doves'.

Too bad some modern day sailors insist on sailing as if Noah story was anything but a story.

Cheers,
b.
we do know he kept a good lookout with Mk 1 eyeball... otherwise he wouldn't have spotted Mt Ararat...
Unless...
He wasn't keeping a good lookout and just happened to run ito it....
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Old 05-09-2016, 17:02   #264
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Re: AIS, Receiver or Transmitter

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Originally Posted by El Pinguino View Post
we do know he kept a good lookout with Mk 1 eyeball...

Not at all. God looked out for him because he wasn't a sinner.

It was the first satellite navigation.


Mark
(Not bad from an Atheist lol)
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Old 05-09-2016, 17:31   #265
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Re: AIS, Receiver or Transmitter

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Originally Posted by Dockhead View Post


MARPA is utterly useless on all the crappy recreational radars I've ever had, so I never used it for collision avoidance. Before AIS, I used (and that's what I would have done on your ship, if the ARPA had gone down) -- the EBL. Just put the EBL on the target and you see in just a few sweeps how you're crossing. If he's walking down the EBL then you know you have a problem. This works even with our crappy recreational radars with very poor bearing discrimination, as the bearing errors will average out over a few sweeps.
Oh no you won't... no way can you see whats going on 'in just a few sweeps'.

Simply the best way to use a yacht radar to establish risk of collision is to run 'target tails' ( name varies by manufacturer ) . Assuming you can maintain a reasonably steady course you can also establish quite a good CPA this way. Edit... on multiple targets all at the same time...

Back in the dark ages pre target tails that was exactly what you would be doing with the chinagraph pencil and the 6 minute system.
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Old 05-09-2016, 17:36   #266
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Re: AIS, Receiver or Transmitter

He he he. ;-)

Noah was lucky not to know that if he had stuck to farming (rather than go rafting) we would not have to face this ...

Cheers,
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Old 05-09-2016, 17:49   #267
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Re: AIS, Receiver or Transmitter

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Originally Posted by MarkJ View Post
Not at all. God looked out for him because he wasn't a sinner.

It was the first satellite navigation.


Mark
(Not bad from an Atheist lol)
+1!

Bravo! Doves for the his ais and God for his gps!

Cheers,
Love,
b.
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Old 05-09-2016, 17:56   #268
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Re: AIS, Receiver or Transmitter

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+1!

Bravo! Doves for the his ais and God for his gps!

Cheers,
Love,
b.
We should all be so blessed.
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Old 05-09-2016, 19:54   #269
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Re: AIS, Receiver or Transmitter

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Have never seen a single comment from Dockhead that advocated abandoning common sense. Following the rules IE Colregs and using common sense are in no way mutually exclusive.

Broken record? Pot and kettle?



I have frequently contacted large ships at sea (but never ran across the QEII) and they were always glad or even grateful that I did so and confirmed our intentions were compatible with avoiding a collision.




Well more or less yes, but within the context of the Colregs. If cruisers unilaterally and randomly start altering course to avoid big ships in ways that do not follow Colregs then it is quite possible or even likely that this could be confusing the situation and increase instead of decrease the chance of collision.

Here is one example that I think clearly demonstrates the issue. You are headed east under sail, to your port is a ship headed south that appears to be on a constant bearing. "Oh" you say, "I need to use common sense and courtesy so I will stop or reverse course to let the ship proceed." Meanwhile that ship has just altered course to starboard a couple of degrees to allow you to cross ahead. Now the ship will have to figure out what you're doing and how to alter course again (or not) to avoid you.
A friend had this problem. He was headed down the west coast. He saw a ship and decided to alter course. He then figures out the ship is on a collision course again. This happened a couple of times, then he hears on the radio the ship calling the coast guard something to the effect that some idiot out here is trying to kill himself, he keeps altering course in front of me.
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Old 06-09-2016, 07:19   #270
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Re: AIS, Receiver or Transmitter

Quote:
Originally Posted by El Pinguino View Post
Oh no you won't... no way can you see whats going on 'in just a few sweeps'.

Simply the best way to use a yacht radar to establish risk of collision is to run 'target tails' ( name varies by manufacturer ) . Assuming you can maintain a reasonably steady course you can also establish quite a good CPA this way. Edit... on multiple targets all at the same time...

Back in the dark ages pre target tails that was exactly what you would be doing with the chinagraph pencil and the 6 minute system.
Trails are great because they show every target on the screen. If you can get a straightedge on them (not usually possible on a yacht radar) you can even work up a quick & dirty CPA with them.

But the EBL is king for a vivid graphical presentation of a collision course. First thing you do with a priority target is put the EBL on it -- at least that's the way I was taught to do it.
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