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Old 18-05-2013, 16:53   #271
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Originally Posted by Dockhead View Post

Query whether these situations (also, the tight quarters situation mentioned in the previous post) are really suited to AIS in its present form. Can it give useful information? If you are getting a position update only every 30 seconds from Class B transponders -- at best! -- then by the time you're a few cables away, surely the predicted course and so forth of Class B targets starts to become fairly useless, and the alarms become pure noise. No?

Maybe it's worth thinking a bit about how we use it. I, for one (and not presuming to speak for others), don't look at it when entering a crowded harbor with dozens of vessels at close quarters. It seems to me that AIS and its calculations of collision courses is not useful at very close quarters with small vessels are being mostly hand steered. I, for one, use the Mark I eyeball in such situations and ignore the plotter.

I suspect the system is not even designed, really, for this kind of situation, and I'm not quite sure how it could be.

So maybe not just the system, but the operator also needs some adjustment.

I appreciate that there are some valid arguments in here [in this very point, I mean] for no one caring whether transponders are switched off in the berth, or not, which is not to say necessarily that they are persuasive.
+1 Dockhead. Keep looking out the window folks not listening to alarms.

Dave
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Old 18-05-2013, 17:14   #272
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I don't disagree with Evans assertion. Yes in harbour with the boat put away , AIS should be switched off , equally so should radar and I would go as far to say that VHF activity should be minimised. Equally nav lights should also be switched off

These are good practices.


However , the rules ( in general ) don't require any of this. And then" commons" argument is very weak


Also , the IMO resolution specifically allows port authorities to control in port usage of AIS , so we may see rules for class B operation in dense areas. so be it , unlike some , I have no problems with such rules.

The issue of Class B and class A and filtering etc is a fundamental weakness of AIS. With increasing class B transponders , it will become more of an issue. However the COLREGS do require any vessel to use all aids to navigation , so woe betide any ship in collision with a yacht using a class B transponders and having class B filters out.

Evans problem is correct in that it exposes the weakness of class B, in such dense areas , whether the vessels are docked , moving slowly , moored , anchored ( I mean what about large fields of anchored class Bs ) ( what about regattas etc )

The users equipment will have to get better , filtering will have to be adaptive and YES users will have to disable alarms in high density areas , no more then I disable MARPA alarms in rough conditions.

Things going beep beep down below , while you are conning into a harbour are not very useful in my experience

Dave
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Old 18-05-2013, 17:29   #273
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Re: Please turn your AIS off when docked/moored/anchored

This is starting to sound like a Philosophy 101 class. I think the sheeps path through the common area should be controlled.
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Old 18-05-2013, 17:31   #274
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Re: Please turn your AIS off when docked/moored/anchored

By the way, as far as filtering large numbers of UNDERWAY vessels (Mark's priority), I have commented in the past to two AIS manufacturers that they are not giving us what we need. Currently all units (that I am aware of) apply the same set of filter to all targets. What is needed are different filters specs for different classes of underway targets. For instance, you should have different filter specs (CPA & TCPA) for vessels that are give way to you, than for vessels that you give way to. I also think you should have different filter specs for large commercial vessels that take a long time & distance to maneuver than for small fast speed boats.

With today's cpu power these sort of vessel specific filters should not be difficult to program or to apply, but no-one yet is doing it.
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Old 18-05-2013, 17:41   #275
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By the way, as far as filtering large numbers of UNDERWAY vessels (Mark's priority), I have commented in the past to two AIS manufacturers that they are not giving us what we need. Currently all units (that I am aware of) apply the same set of filter to all targets. What is needed are different filters specs for different classes of underway targets. For instance, you should have different filter specs (CPA & TCPA) for vessels that are give way to you, than for vessels that you give way to. I also think you should have different filter specs for large commercial vessels that take a long time & distance to maneuver than for small fast speed boats.

With today's cpu power these sort of vessel specific filters should not be difficult to program or to apply, but no-one yet is doing it.
This can't be done with class B , all you really have is speed and heading info. Even the static data is no real use.

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Old 18-05-2013, 18:00   #276
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Re: Please turn your AIS off when docked/moored/anchored

Dave, I agree that of course you cannot do it 'perfectly', as even a human cannot do it perfectly on a foggy day, but you can approximate it as a human does.

For instance for the second the part (eg different filters for large commercial vessels vs small fast speed boats) you could approximate 'large commercial vessels' as "type A AIS plus long LOA (which is in the Type A message format)", and for small speed boat = "fast SOG + history of fast rate of change of COG"

For the first part (stand on vs give way) you could approximate it as vessels crossing from your right = stand on and vessels crossing from your left or over taking as give way. That's about what you would do with radar in any case.

There might be a 'general purpose' filter spec for vessels that could not be placed in a category.

The point is do it a little smarter, not perfectly.
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Old 18-05-2013, 18:17   #277
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Re: Please turn your AIS off when docked/moored/anchored

Class-B also transmits vessel length and beam, as part the GPS antenna location fields. I have seen these values incorrectly programmed, but they generally seem OK.

As for alarm behavior depending on a vessel's right-of-way status, that's going to be a tough one. You will need to know whether a ship is in a narrow channel, or has a tug attached (and not all tugs carry AIS), or is otherwise restricted in their ability to maneuver. For sailboats you would need to know port/starboard wind angles, etc. As much as I go on and on about needing better alarm algorithms, this is a really difficult problem, and I don't know that I would trust an automated solution.

But, you can't really ask that everyone except those who are of concern to you turn off their transponders, and there will be many of those who are "legitimately" transmitting.

Evans, as you said, "a little smarter" is still better than what we have now.
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Old 18-05-2013, 18:18   #278
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Originally Posted by estarzinger View Post
Dave, I agree ....

The point is do it a little smarter, not perfectly.
Sure , all in favour of that, smarts are god in electronics, it only deals with some of the issues though

Dave
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Old 18-05-2013, 18:33   #279
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Re: Please turn your AIS off when docked/moored/anchored

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Originally Posted by estarzinger View Post
With today's cpu power these sort of vessel specific filters should not be difficult to program or to apply, but no-one yet is doing it.
I think this would be a great open source project, as an add on for open CPN. A very good open source filter would force manufacturers to follow suit and improve their filters. Although I think their is a big danger of over reliance on an such an alarm.

An additional useful alarm would be for a fast overtaking boat. maybe add some different alarm sounds to indicate the direction of the danger. I can see the day when it is like a car GPS giving verbal instructions "CPA alarm, Vessel 3 points to port." I think aircraft have similar, with a voice warning system? It helps to look at the aircraft industry as they are about 10-20 years ahead in terms of bridge team management.
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Old 18-05-2013, 18:42   #280
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I would say however its a brave AIS manufacturer that will emphasis speed filters over proximity. I suspect proximity will always be the prevalent filter.

Dave
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Old 18-05-2013, 18:43   #281
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Re: Please turn your AIS off when docked/moored/anchored

Yes, filters could be greatly improved. Always. Don't know how they would always prevent the OP's issue without becoming so specific as to be useless. But I am willing to hope.

Dockhead nailed it - in a harbor situation, audio alarms are useless and eyeballs rule. Not only in looking outside the dodger (I never accused or even believe that is not possible with Evans), but in looking at an appropriate display that is appropriately setup to accommodate this situation.

The best harbor "filter" is to simply interface the AIS with a chart plotter, computer or radar display and turn off the alarms. All AIS units make this very easy. Then, the clusters of class B signals from boats right on the shore are numbnuts in marinas who did not turn off their transponder. You know this because they are clustered and right on the shore line. The class A vessel stopped around the corner in the shipping channel should be given attention. You know this because it has class A data and is actually in the navigable waters you are in. In fact, it is in the channel waters and not on the shoreline. As you swing your vessel through a turn, you see those clusters of numbnuts move through your electronic vision field and no longer be a threat (this takes 1-3 seconds of eyeball time from watching the real situation outside the dodger). But that stalled commercial ship is still sitting right in the nice blue channel.

Even on the Vespar radar-type display only, I have a difficult time understanding why clusters of targets not in ones heading or future heading, and within the appropriate distance expected causes problems. Visually, that is. Alarms are another issue, but I personally wouldn't have the klaxons ringing in a harbor anyway. And klaxons ringing seems to be what Evan's problem boils down to.

If the type of display being used is causing the problem, then the problem is the type of display being used. Easy solution.

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Old 18-05-2013, 18:50   #282
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Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by goboatingnow View Post
I would say however its a brave AIS manufacturer that will emphasis speed filters over proximity. I suspect proximity will always be the prevalent filter.

Dave
I have owned two AIS black box units and they did not have "filters" at all. Instead, they required me to set filters on whichever display or software I am using for them. I can set them anyway I want, including changing colors based on type of vessel and my perceived danger of it, speed, distance, anchored, etc. I have a chartplotter and a handful of computer plotting programs that give me much leeway with filter criteria.

If one buys an AIS with display like the Vespar in use by the OP, is one really limited to just a few preset filters? Can't these be adjusted or over-ridden? If not, this doesn't seem like a good purchase.

That is not a snarky or rhetorical question - I don't have any knowledge there.

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Old 18-05-2013, 18:58   #283
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Re: Please turn your AIS off when docked/moored/anchored

^^

The filters on the Vesper can be adjusted - you can set all of "target range', 'target speed', 'target cpa', 'target tcpa', 'guard alarm range', 'your speed'. You can set these however you like, differently in 4 'preset' filters, so you can toggle all of them at once between the 4 different filter situations (called anchored, harbor, coastal and offshore). I have seen a pc program that can also use the status and description fields but the vesper cannot do that.

By the way, the vesper unit with the screen can also feed a plotter display (and I have it so it shows targets both on its own screen and on my plotter).

But (in all the units I am aware of) when you set the filter they apply to all targets. My point is that you might want (I do) different criteria for different vessels - I want longer CPA and TCPA for ships than I do for small maneuverable speed boats.
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Old 18-05-2013, 18:58   #284
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Re: Please turn your AIS off when docked/moored/anchored

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The only comment I have is one I've resisted making: it isn't called "The Commons".

It's called "The Tragedy of The Commons."

It isn't used to to demonstrate what should happen, (there are several versions of it, involving sheep, footpaths, snow & ice, and so on) it's used to demonstrate what does happen, and how humans always end up choosing what they perceive is best for them, even at the expense of others.

The italics I've added are important, and part of the point. The lesson goes on, but when one leaves the rails this early, the rest of it doesn't really matter.

When someone refers to The Tragedy of The Commons and indicates that it demonstrates some lesson about how we should all learn to stay off the grass (keep our sheep off the grass, clear the sidewalk of ice, etc.) I conclude that he or she does not understand the concept.

Applying the concept of The Tragedy of The Commons to AIS correctly yields this conclusion: people will walk (or cut, depending on version) across / let their sheep graze / fail to clear the sidewalk on the commons because they perceive that's what's best for them.

They will, therefore, either turn their AIS off or leave it on, depending on their perception of what's best for them.

This will result in footpaths worn across the commons, sheep grazing on it, and some AIS units off, others on.

That is the starting point for reasonable discussion, and I think it's exactly on point in a discussion about turning AIS off at the dock.

The Tragedy of The Commons does not tell us to keep our sheep off the commons.

It tells us that there will always be sheep on the commons.
Ah, finally someone who actually understands the purpose of that viral meme.

I was taken aback at first about the description of sheep grazing on an English commons because I have met the parable in many forms such as the footpaths, cows in Africa, ice on sidewalks, etc, but not actually english sheep in common greens.

And yes, I agree that pulling this up constantly whenever these types of issues come up is a cheap and easy way to avoid actually thinking in a debate - which always derails the discussion. In fact, almost all of the times I have had the pleasure of meeting it can be described that way.

Unfortunately, it appeals to emotions in the guise of "common sense", and people "get" that and come to a full stop.

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Old 18-05-2013, 19:14   #285
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Re: Please turn your AIS off when docked/moored/anchored

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humans always end up choosing what they perceive is best for them, even at the expense of others.
I am sorry but that is just false BS.

You tell that to the wife of the fireman who dies trying to save lives in a burning building or the solder who falls on a grenade to save his buddies!

Closer to home, tell that to the cruisers who help other cruisers for no compensation, reward or recognition.

I would suggest you are missing the lesson - selfish humans will ruin a public commons but moral ones can maintain one.
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