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Old 09-04-2019, 08:34 AM   #21
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The upside to AIS around the Chesapeake is being able to see the boat names. Kinda fun seeing the various names. It's annoying seeing just an MMSI number. I have checked the info for some AIS targets, but mainly just for curiosity. I'll have to remember to check on the ones squawking just an MMSI to see if they're actually sending useful data (length, beam, heading, etc).
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Old 09-04-2019, 09:42 AM   #22
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Yep, following some friends on a moon-less night and it was unnerving seeing us over-taking their AIS marker... and then having it jump forward again, over and over.

Radar didn't have that problem as the sweep is generally every second.

But I'll confess to not having learned anywhere near enough about the Furuno setup in our boat. We just don't boat that often at night or in conditions with limited visibility.

I didn’t use the radar on my sailboat unless there were visibility issues; running at night, fog, heavy rain, etc... Being out in the cockpit, open to the elements, I always had very good situational awareness of other boats. However, over the past couple years I am finding that I am using the radar most of the time now. Sitting in the pilothouse I’m not as aware of traffic coming from behind me. The radar is really handy for that. I don’t use the alarms because there is usually so much traffic that it would always be going off. However I do select targets frequently and use that information.

I do love the AIS though. I only have a receiver but want a transceiver some day.
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Old 09-04-2019, 11:25 AM   #23
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I think that an AIS transponder is a necessary piece of equipment when in the vicinity of commercial traffic. I want them to be able to call me by name. We travel in the fog. Just a couple of weeks ago in Buzzards Bay, crossing the shipping lane, fog, and a knot and 1/2 of current I heard a tug and barge hailing the “vessel at such and such a location”. The tug was coming down stream. Not a place for the tug to be guessing what your intentions are. They are always happy to tell you what they want you to do and I am most happy to obey. Wasn’t me they were contacting as I was over a mile upstream from the tug. The other guy never responded and maybe never knew he was in the tugs “sights”
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Old 09-04-2019, 11:33 AM   #24
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I think that an AIS transponder is a necessary piece of equipment when in the vicinity of commercial traffic. I want them to be able to call me by name. We travel in the fog. Just a couple of weeks ago in Buzzards Bay, crossing the shipping lane, fog, and a knot and 1/2 of current I heard a tug and barge hailing the “vessel at such and such a location”. The tug was coming down stream. Not a place for the tug to be guessing what your intentions are. They are always happy to tell you what they want you to do and I am most happy to obey. Wasn’t me they were contacting as I was over a mile upstream from the tug. The other guy never responded and maybe never knew he was in the tugs “sights”
I've heard a few similar announcements, and wondered if the target vessels were likewise aware. That and it made me aware of the times I didn't have my VHF on and if I wasn't likewise unaware. I always try to adjust my course to be effective for everyone, that means doing it ahead of time and thus to CPA.
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Old 09-04-2019, 11:34 AM   #25
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Many AIS systems will give you the age of the latest position report. On a newish Raymarine, this is shown as the "most recently seen" time in the AIS data. Not ideal as you must subtract the current time from it to see the age. OpenCPN shows it as a live running age in the AIS data, counting up in seconds. This is much more useful. Class A will rarely get older than a few seconds before being refreshed provided you are within good range. Class B will go to 30 seconds or even several minutes as the transmissions are not as frequent or as powerful. Chart plotters often depict the target, even if the data is old. Some will shade the target to indicate old data.

Yes, AIS input can be abused, just as radar input can be. As TT suggested, it is the operator that is the weak link. i'd prefer good AIS data over any radar data, but you must take, understand, and make use of what you get.
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Old 09-04-2019, 12:50 PM   #26
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AIS data may be more informative, but RADAR is real-time constant bearing , decreasing range ...

How does it get better than that for avoiding collision? More info, but none better.


Don't want to be guessing on how current the AIS info is when rounding a bend and the CPA is in seconds.
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Old 09-04-2019, 01:00 PM   #27
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AIS data may be more informative, but RADAR is real-time constant bearing , decreasing range ...

How does it get better than that for avoiding collision? More info, but none better.


Don't want to be guessing on how current the AIS info is when rounding a bend and the CPA is in seconds.
No argument here. Radar is near real time and doesn’t lie. But the AIS data adds to the benefit. Given a choice it would be Radar.
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Old 09-04-2019, 02:10 PM   #28
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We were crossing Lake Ontario in an extremely heavy rain, the worst I have ever been underway in. Our 4kw radar was in white out mode due to the rain. There were 2 freighters crossing our course and the only way I knew they were there was the AIS. I could see them on the plotter but I couldn’t see anything on the radar. One obviously would cross well ahead of us. The other was on a collision course with us. We were stand on and they were give way. As I was reaching for the mic the freighter called us by name. I don’t know if he was able to see us on radar or not but he could see us via AIS since he knew our name. He stated his intention to turn to cross behind us. Without AIS I would have not known that he was there and maybe he would have not known we were there either. His radar may have been able to punch through the rain, I don’t know. But this one time paid for the AIS.
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Old 09-04-2019, 02:23 PM   #29
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One too many times a transponding boat was already past me and the AIS target was still ahead....I don't trust it worth spit compared to RADAR for close aboard relative position info...
Yep, have seen that often enough around here, too. Nice to have AIS, but RADAR way more useful for time-sensitive info. Especially given maybe 1% (or less?) of boats here in the Chesapeake transmit an AIS signal...



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The upside to AIS around the Chesapeake is being able to see the boat names. Kinda fun seeing the various names. It's annoying seeing just an MMSI number. I have checked the info for some AIS targets, but mainly just for curiosity. I'll have to remember to check on the ones squawking just an MMSI to see if they're actually sending useful data (length, beam, heading, etc).
Sometimes it takes a while for our system to resolve an MMSI into a name. Dunno why... Maybe the MMSI transmits every time, name only every other sometimes?

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Old 09-04-2019, 02:25 PM   #30
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I agree that radar is critical, except for when it doesn’t work as in my post above.
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Old 09-04-2019, 02:40 PM   #31
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We were crossing Lake Ontario in an extremely heavy rain, the worst I have ever been underway in. Our 4kw radar was in white out mode due to the rain. There were 2 freighters crossing our course and the only way I knew they were there was the AIS. I could see them on the plotter but I couldn’t see anything on the radar. One obviously would cross well ahead of us. The other was on a collision course with us. We were stand on and they were give way. As I was reaching for the mic the freighter called us by name. I don’t know if he was able to see us on radar or not but he could see us via AIS since he knew our name. He stated his intention to turn to cross behind us. Without AIS I would have not known that he was there and maybe he would have not known we were there either. His radar may have been able to punch through the rain, I don’t know. But this one time paid for the AIS.
Exactly my point. Radar is great but more is better.
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Old 09-04-2019, 02:42 PM   #32
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And that trusty VHF comes in pretty handy. Always scanning 16/13 when in poor visibility.
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Old 09-04-2019, 03:37 PM   #33
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Sometimes it takes a while for our system to resolve an MMSI into a name. Dunno why... Maybe the MMSI transmits every time, name only every other sometimes?

-Chris

Yes, that's exactly how it works. You "dynamic" data is transmitted regularly updating you position, COG, and SOG. And "static" data is transmitted much less frequently, so the boat's name, dimensions, call sign, etc. can take a while after first contact to populate.


The only danger with AIS is not understanding what it's telling you, and what it's not telling you. Every tool has it's limitations, and knowing them is just as important as knowing the tools strengths.
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Old 09-04-2019, 07:55 PM   #34
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You can "what if" to death... the prudent mariner uses all available aids to navigation. Electronic, visual,paper etc. Anybody with more than a weeks experience can come up with a "near miss" he did this, he should have done that, I am right , he is wrong etc.... We all learn by experience and our mistakes. The Rules of the road are the bible but even they say you should give way...
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Old 09-04-2019, 08:10 PM   #35
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The lie that radar tells is one of omission. You can't always see everything with it, and in some conditions you can't see anything with it. A recently transmitted AIS report is both more accurate and more informative than radar. The mistake in using either is assuming they contain everything you need to know.
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Old 09-04-2019, 09:19 PM   #36
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I don’t know if he was able to see us on radar or not but he could see us via AIS since he knew our name. He stated his intention to turn to cross behind us. Without AIS I would have not known that he was there and maybe he would have not known we were there either. His radar may have been able to punch through the rain, I don’t know. But this one time paid for the AIS.
I've had my radar washed out by rain many times on the ship. With a bit of fiddling, you can clear the picture up, but with a smaller target like any of our boats, it's entirely possible that his radar never picked you up. That's a great time to have AIS.
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Old 09-04-2019, 09:28 PM   #37
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We were crossing Lake Ontario in an extremely heavy rain, the worst I have ever been underway in. Our 4kw radar was in white out mode due to the rain. There were 2 freighters crossing our course and the only way I knew they were there was the AIS. I could see them on the plotter but I couldn’t see anything on the radar. One obviously would cross well ahead of us. The other was on a collision course with us. We were stand on and they were give way. As I was reaching for the mic the freighter called us by name. I don’t know if he was able to see us on radar or not but he could see us via AIS since he knew our name. He stated his intention to turn to cross behind us. Without AIS I would have not known that he was there and maybe he would have not known we were there either. His radar may have been able to punch through the rain, I don’t know. But this one time paid for the AIS.
You have to learn how to tune your radar in heavy rain. I'm sorry for the tone, but that's just no excuse. And yes, I understand you are talking about very heavy rain. What about boats without AIS? How you going to find them?
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Old 09-04-2019, 10:07 PM   #38
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You have to learn how to tune your radar in heavy rain. I'm sorry for the tone, but that's just no excuse. And yes, I understand you are talking about very heavy rain. What about boats without AIS? How you going to find them?

Braille?
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Old 09-04-2019, 10:19 PM   #39
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You have to learn how to tune your radar in heavy rain. I'm sorry for the tone, but that's just no excuse. And yes, I understand you are talking about very heavy rain. What about boats without AIS? How you going to find them?
I know how to tune my radar. It could not punch through the rain, did I mention that I don’t know if I had ever been in that heavy of a rain. Sometimes conditions are beyond not only your control but beyond the radars capability. And I was not making an excuse, just stating a fact.
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Old 09-05-2019, 06:15 AM   #40
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The lie that radar tells is one of omission. You can't always see everything with it, and in some conditions you can't see anything with it.

A recently transmitted AIS report is both more accurate and more informative than radar. The mistake in using either is assuming they contain everything you need to know.

Sure, but that kind of "lie" applies to AIS as well. If 99% of boats nearby don't transmit AIS...

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