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Old 07-06-2014, 16:40   #31
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Re: Thoughts about AIS

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Originally Posted by colemj View Post
Like I said earlier - we go through the Panama canal entrance a couple of times each year where there are literally hundreds of boats at anchor, milling around in circles and charging forward at full speed. To top it off, there is a large breakwater that one cannot see over with a narrow entrance that allows 2 ships to pass through very closely. We have to get through all the ships and through this breakwater entrance whose goings on on the other side is blind to us (but not blind to AIS).

In your situation above, a quarter mile (if I understand "cable" correctly - who uses "cable" as a distance measurement?) is no problem to us in a shipping lane and none of the ships would be a danger. If it appeared that a ship was going to be much closer than that, the AIS display with predictor lines would easily tell me the situation without needing to know bearings and rate of change.

Heck, I would probably drop down a knot or two in speed since I am under power and see how the situation changes - that is apparent in 30 seconds or so. Or maybe change course 5 degrees and see. That also will tell me a lot very quickly. Unless I hadn't been paying attention and only noticed those two ships bearing down on us at the last moment, I really don't see the problem in your example.

Now you want something to really screw around with you - try a few Disney cruiseliners off a major port at night. Those guys just randomly circle around waiting for daylight to enter a harbor. One minute they are ringing your alarms and the next they are heading off in a different direction, only to reverse and come at you again. You can't see your AIS display because of all the floodlights, disco balls, laser lightshows, etc blinding you...

Perhaps we are just more used to using AIS integrated into our navigation mode? We certainly go through complicated and busy shipping lanes/ports with little problem with navigation.

Mark
Well, these problems are all different than those faced by the sailor cutting through a dense lane of fast-moving ships. This has been very useful -- shows that our problems here are quite narrow and specific to our circumstances. I guess most people just don't need it -- which is maybe why Navico don't provide it -- but we really need to know how the bearings of AIS targets are changing.
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Old 07-06-2014, 16:47   #32
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Re: Thoughts about AIS

I'm pretty sure there are a lot of cruisers on here who don't have AIS yet, so it might be really useful in this discussion for those who have it to attach pictures of their AIS presentation. It's not easy to follow these discussions without seeing what the posters are seeing, and it might also be helpful for those who have different equipment brands.

That might also help us choose how we want to enter this brave, cool new world of gadgets. (I am in the process of buying my first cruiser-sized boat and all of this is very interesting to me.)

I like the Vesper design with the dedicated screen, but it seems like it might be somewhat confusing because it overlays only a base map and not detailed chart info. On the other hand, that does reduce clutter and potential confusion. How useful do you guys think it is to have the dedicated display as opposed to the chart overlay on your regular system?

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Old 07-06-2014, 16:50   #33
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Re: Thoughts about AIS

I am yet to fiddle with our new Raymarine e125, but if it is the same as our older E125W the AIS CPA is definately lacking. It didnt show clearly if vessels would pass ahead or astern. We have the raymarine 650 and leaving the mini USB connected and running it into OpenCPN gives fantastic detail. I usually refer to that if there is any question.
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Old 07-06-2014, 16:52   #34
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Re: Thoughts about AIS

Quote:
Originally Posted by David Dennis View Post
I'm pretty sure there are a lot of cruisers on here who don't have AIS yet, so it might be really useful in this discussion for those who have it to attach pictures of their AIS presentation. It's not easy to follow these discussions without seeing what the posters are seeing, and it might also be helpful for those who have different equipment brands.

That might also help us choose how we want to enter this brave, cool new world of gadgets. (I am in the process of buying my first cruiser-sized boat and all of this is very interesting to me.)

I like the Vesper design with the dedicated screen, but it seems like it might be somewhat confusing because it overlays only a base map and not detailed chart info. On the other hand, that does reduce clutter and potential confusion. How useful do you guys think it is to have the dedicated display as opposed to the chart overlay on your regular system?

David
I've not used a separate AIS display, but I would think that most people would really want to see AIS targets displayed in relation to radar targets and in relation to their chart display. On top of that, few cruising boats I know have an excess of space for extra displays. So it's a bit hard for me to imagine why anyone would go for a separate display unless they just don't have a nav system capable of displaying AIS data, but maybe someone who uses one can name some other reasons.
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Old 07-06-2014, 17:06   #35
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Re: Thoughts about AIS

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Originally Posted by Dockhead View Post
Thanks, that's useful!

I don't care much about automatic acquisition, but the ability to test a proposed change of course or speed would be terrific!! Wow, I wish my AIS set could do that, too.
I think one of the main reasons that we regular yachtsmen have appreciated AIS over Radar is the poor stabilization of Radar on a small yacht bouncing and slewing around.

Target data jumps around so less confidence in the MARPA.

Are there "yacht radars" that have a slower refresh rate that averages out heading or uses own ship COG to help stabilize the Target data?
If not...I think this would help.
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Old 07-06-2014, 18:14   #36
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Re: Thoughts about AIS

Crossing ahead or behind? Resolving how much room is there? These issues are easily resolved by a chart plotter such as Nobletec Odyssey, and perhaps others that can show you this:

https://www.dropbox.com/s/oph781y2ls...%20Display.JPG

The red is your boat moving slowly, and the blue "Clipper 3" is moving at about 30 knots. The lines emanating from each vessel show where each will be at CPA. The line between them is the CPA separation. Time to CPA and CPA separation distance is shown as text on the right side of the screen.

You can easily see that if both hold course and speed, you will pass behind Clipper 3. The display is dynamic. If you adjust your course or speed you will see the picture update. If the graphic is too small for you to see the separation, zooming in clarifies it.

This display is automatically brought up for the most critical target with a close passing, but you can create it for any target with a couple of mouse actions.

I believe that this is the simplest and most effective means of dealing with these questions that have been discussed in this thread.
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Old 07-06-2014, 18:36   #37
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Re: Thoughts about AIS

Quote:
Originally Posted by Pelagic View Post
I think one of the main reasons that we regular yachtsmen have appreciated AIS over Radar is the poor stabilization of Radar on a small yacht bouncing and slewing around.

Target data jumps around so less confidence in the MARPA.

Are there "yacht radars" that have a slower refresh rate that averages out heading or uses own ship COG to help stabilize the Target data?
If not...I think this would help.
It does not do this on our system. Our compass provides 20 data points per second and our GPS provides 5 data points per second. Our ARPA is rock steady. However, it is slower to respond to a change than AIS because it relies on internal calculations of differences between scan sweeps rather than a vhf broadcast of the entire ship's info.

Mark
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Old 07-06-2014, 18:45   #38
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Re: Thoughts about AIS

Quote:
Originally Posted by St. Elsewhere View Post
Crossing ahead or behind? Resolving how much room is there? These issues are easily resolved by a chart plotter such as Nobletec Odyssey, and perhaps others that can show you this:

The red is your boat moving slowly, and the blue "Clipper 3" is moving at about 30 knots. The lines emanating from each vessel show where each will be at CPA. The line between them is the CPA separation. Time to CPA and CPA separation distance is shown as text on the right side of the screen.

You can easily see that if both hold course and speed, you will pass behind Clipper 3. The display is dynamic. If you adjust your course or speed you will see the picture update. If the graphic is too small for you to see the separation, zooming in clarifies it.

This display is automatically brought up for the most critical target with a close passing, but you can create it for any target with a couple of mouse actions.

I believe that this is the simplest and most effective means of dealing with these questions that have been discussed in this thread.
Yes, that is what I have been trying to explain. Everything you need to know is in a quick glance at composite dynamic graphic data. Just looking at that picture without consciously picking apart all the data involved tells your brain all it needs to know in a synthesized "picture" way. This type, or similar, graphics are on the systems we use the most - Coastal Explorer and to a lesser extent our Furuno.

I am really starting to think that all of this debate around AIS, radar, etc (many other threads besides this one) is really just a difference between a good data display system and poorer ones, coupled with familiarity with using these data.

Mark
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Old 07-06-2014, 21:00   #39
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Re: Thoughts about AIS

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What exactly is this "big difference"? I have just trawled the interweb again, and still can't find any difference, other than manual versus automatic target acquisition. AFAIK, it's almost exactly the same thing, but I would be glad to be enlightened, if I'm wrong and if there really is some "big difference".
ARPA is NOT:

Quote:
Originally Posted by Dockhead View Post
.....MARPA requires very active use -- acquisition of specific targets, etc....... MARPA, even with a high end heading sensor like I have, even with a really good radar, is very inexact -- probably because radar inherently cannot be very accurate in determining bearings (it is very accurate for range)........ MARPA cannot track more than a few targets at once, and the operator has to regularly re-acquire targets as they drop on and off the radar screen. MARPA doesn't identify the targets, so you have to keep up with them yourself. ....... spending a lot of time working MARPA targets. ...... not worth working in MARPA this far out.
All the complaints you've had with MARPA don't exist with a good implementation of ARPA.

As Mark explained, a good ARPA is as automatic as AIS, albeit, slightly slower to calculate changes.
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Old 08-06-2014, 00:14   #40
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Re: Thoughts about AIS

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Originally Posted by colemj View Post
It does not do this on our system. Our compass provides 20 data points per second and our GPS provides 5 data points per second. Our ARPA is rock steady. However, it is slower to respond to a change than AIS because it relies on internal calculations of differences between scan sweeps rather than a vhf broadcast of the entire ship's info.

Mark
Yes your system is great.
Unfortunately many yachtsmen only know and use an "unstabilized " heads up display that can make you dizzy looking at it

AIS is much simpler by comparison to understand BUT gives no info on Non users.... which we see a lot of in South China Sea
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Old 08-06-2014, 00:44   #41
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Re: Thoughts about AIS

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In your situation above, a quarter mile (if I understand "cable" correctly - who uses "cable" as a distance measurement?)
A cable is a very convenient unit if you are working in knots and nautical miles. 1/10 of a nautical mile.
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Old 08-06-2014, 01:28   #42
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Re: Thoughts about AIS

Quote:
Originally Posted by David Dennis View Post
I'm pretty sure there are a lot of cruisers on here who don't have AIS yet, so it might be really useful in this discussion for those who have it to attach pictures of their AIS presentation. It's not easy to follow these discussions without seeing what the posters are seeing, and it might also be helpful for those who have different equipment brands.

That might also help us choose how we want to enter this brave, cool new world of gadgets. (I am in the process of buying my first cruiser-sized boat and all of this is very interesting to me.)

David
Here the manual with examples and screenshots from OpenCPN:
AIS | Official OpenCPN Homepage

A great bunch of the features discussed here are implemented - target information at mouse over, target list, alarms, COG predictor, where-will-we-pass(CPA/TCPA), target-track, .....

Just have a look.

bcn
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Old 08-06-2014, 02:53   #43
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Quote:
Originally Posted by bcn View Post

Here the manual with examples and screenshots from OpenCPN:
AIS | Official OpenCPN Homepage

A great bunch of the features discussed here are implemented - target information at mouse over, target list, alarms, COG predictor, where-will-we-pass(CPA/TCPA), target-track, .....

Just have a look.

bcn
Very, very powerful implementation of AIS . Wow, what a terrific program.

If I understood correctly, you will see how you pass another vessel via the blue dot on the projected COG line which shows your predicted position at CPA. It doesn't say whether there is a corresponding blue dot on the target vessel's projected COG line - you would need that. But I presume there is, right? Extremely clever, and more usable for less skilled navigators, than my system. And altogether better than my system, since it requires less interpretation - you just see . Awesome!

Other things I really liked:

APRS targets also shown - cool!

Nav status shown using corresponding day shapes - clever!

Size and dimensions of target can be shown based on LOA, beam, and GPS position static data of target - very clever!

Total flexibility and configurability (Apple product users will have mental breakdowns ).

Love, love, love it. More kudos to the developers of this totally awesome program,
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Old 08-06-2014, 03:01   #44
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Re: Thoughts about AIS

have a look at my post above, you see the two blue dots and the CPA dotted red line. This will alter immediately is speed or course is changed of either vessels. It shows these details for all AIS targets. Yes its excellent!
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Old 08-06-2014, 03:01   #45
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Re: Thoughts about AIS

Yes, there are reference points on the target's COG predictor as well.

On the to-do-list are clever alarm filter settings for very crowded places, for example the Solent with several hundreds of boats at a summer weekend.
And perhaps profiles for different situation.

Ideas (and implementers) are always welcome

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