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27-08-2017, 03:37
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#151
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Moderator
Join Date: Mar 2009
Location: Denmark (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 33,764
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Re: Collision Avoidance -- Dealing with Multiple Targets
Quote:
Originally Posted by bmz
I don't know what you are doing. I asked Roland what he does about AIS clutter. That doesn't mean that no one else can respond with what they do about AIS clutter; but your post is not responsive to my question in any form or fashion.
Nonetheless this forum does try to educate, so I will respond in that vein.
What ever you do about a small powerboat closing in on you at 20 kn, it will be far more effective if you are not trying to focus on what 40 other class B AIS targets on your chart plotter are doing.
A small powerboat out joyriding may have been all over your chart plotter before he started to head for you. Those other 40 class B targets will also usually change their courses creating intercepts with you many times before seeing you and steering clear. They are basically noise and distract you from real dangers like that powerboat closing in on you at 20 kn. Of course this does not apply to class A targets which are a distinct threat, and to whom you have to yield or give way. But usually they are in channels or traffic lanes and maintain a steady course.
Whatever I do about that small powerboat has nothing to do with whether or not he or I have an AIS. I have had literally thousands of small fast powerboats crossing within a few hundred feet of me. Out of those thousands, maybe a handful times I've had to blow my horn. The only time that they are really a threat to you is if your attention is somewhere else--like the 40 other class B AIS targets on your chart plotter.
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How to deal with "clutter" is entirely relevant to the original theme of this thread.
How to avoid being confused by a multitude of targets depends on what kind of display you have.
Most AIS displays can be adjusted to either bold or change color of vessel symbols depending on different criteria. OpenCPN will change colors; my Zeus displays will bold "dangerous" vessels.
In open water, my definition of a "dangerous vessel" is usually 30 minutes TCPA and 1 mile CPA; in the middle of an empty piece of ocean far from land, maybe 2 or 3 miles. In harbors or approaches, I turn off the alarms and reset the "dangerous vessel" definition to 5 cables and 15 or 20 minutes.
It is then easy to ignore the bolded symbols of pleasure vessels until they get really close, and concentrate on larger vessels where you need to take earlier action.
With OpenCPN, it is really powerful to use the "Show Target CPA" command for the vessels of particular concern, and then you have a graphic display of each crossing you are particularly concerned about, and only those crossings you choose are displayed.
It is inherently difficult to interpret AIS information on a very small screen. In my experience 8" and SVGA is about the minimum for dealing with a moderately complex traffic situation. I don't find the AIS displays on some newer VHF radios to be usable at all.
As Ping noted, basic radar plotting skills are enormously valuable in order to be able to interpret relative motion of vessels and to be able to relate what your screen tells you to what your eyes tell you.
YMMV.
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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27-08-2017, 03:38
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#152
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Registered User
Join Date: Aug 2013
Location: Back in Montt.
Boat: Westerly Sealord
Posts: 8,180
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Re: Collision Avoidance -- Dealing with Multiple Targets
Quote:
Originally Posted by Dockhead
Well, I'm not talking about merely showing red or green or steaming lights in a line -- of course we all know that.
I can do a radar plot by hand, and aspect doesn't enter into it, although you can derive aspect. Relative motion is should be more or less the same whether we reference motion through the water or over ground, the only difference being in case set and drift is not exactly the same between the two vessels.
You're being too modest I think.
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In the not too distant past most ships did not have true motion radar.... and 99.9% of recreational yachts still don't.
( interesting factoid ... my first ship had 'true motion' radar back in the early sixties...Decca or KH radar... a unit on top of what was a standard radar of the era with dials that you entered heading and water speed into.... that at a time when many ships still had no radar at all ... so i have been working with this sort of kit for some time)
Anyway the manual calculation of which you speak... either on a paper plotting sheet next to the radar or with a chinagraph pencil on a reflection plotter... involves marking the 'echo of interest' at 2 x 6 minute intervals...applying your heading and waterspeed vector at 2 x 6 ... and connecting the tails of the two vectors to yield the echo of interest's heading relative to your heading together with her water speed..... this is then what you would, in reduced vis, base your next move on.
The relative motion of the EofI tells you if risk of collision exists.... the track you have produced with your plot gives you the other ship's aspect ..
So it appears you are working with other ship's aspect, water speed and heading without realizing it.
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27-08-2017, 03:50
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#153
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Moderator
Join Date: Mar 2009
Location: Denmark (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 33,764
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Re: Collision Avoidance -- Dealing with Multiple Targets
Quote:
Originally Posted by El Pinguino
In the not too distant past most ships did not have true motion radar.... and 99.9% of recreational yachts still don't.
( interesting factoid ... my first ship had 'true motion' radar back in the early sixties...Decca or KH radar... a unit on top of what was a standard radar of the era with dials that you entered heading and water speed into.... that at a time when many ships still had no radar at all ... so i have been working with this sort of kit for some time)
Anyway the manual calculation of which you speak... either on a paper plotting sheet next to the radar or with a chinagraph pencil on a reflection plotter... involves marking the 'echo of interest' at 2 x 6 minute intervals...applying your heading and waterspeed vector at 2 x 6 ... and connecting the tails of the two vectors to yield the echo of interest's heading relative to your heading together with her water speed..... this is then what you would, in reduced vis, base your next move on.
The relative motion of the EofI tells you if risk of collision exists.... the track you have produced with your plot gives you the other ship's aspect ..
So it appears you are working with other ship's aspect, water speed and heading without realizing it.
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I see what you mean!
Thanks!
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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27-08-2017, 03:55
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#154
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Registered User
Join Date: Aug 2013
Location: Back in Montt.
Boat: Westerly Sealord
Posts: 8,180
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Re: Collision Avoidance -- Dealing with Multiple Targets
Quote:
Originally Posted by Dockhead
You would never do that -- because Class "B" does not broadcast nav status at all -- Bobgarret is referring to TYPE of vessel, which is a different datum and which is part of the static data.
Don't confuse nav status with TYPE of vessel. Type of vessel doesn't change just because you are using sails or not. Here are possible nav status values:
0 = under way using engine
1 = at anchor
2 = not under command
3 = restricted maneuverability
4 = constrained by her draught
5 = moored
6 = aground
7 = engaged in fishing
8 = under way sailing
9 = reserved for future amendment of navigational status for ships carrying DG, HS, or MP, or IMO hazard or pollutant category C, high-speed craft (HSC)
10 = reserved for future amendment of navigational status for ships carrying dangerous goods (DG), harmful substances (HS) or marine pollutants (MP), or IMO hazard or pollutant category A, wing in ground (WIG)
11 = power-driven vessel towing astern (regional use)
12 = power-driven vessel pushing ahead or towing alongside (regional use)
13 = reserved for future use
14 = AIS-SART (active), MOB-AIS, EPIRB-AIS
15 = undefined = default (also used by AIS-SART, MOB-AIS and EPIRB-AIS under test)
https://help.marinetraffic.com/hc/en...Status-Values-
Nav status is broadcast ONLY by Class "A" sets.
Actually the necessity of putting in destination and changing nav status every time is what kept me from putting in a Class A transponder in my own boat. Too much work if you're short handed, and especially if you're single handed.
Now we can buy the new SOTDMA Class "B" sets and I will change to one of those this winter. Addresses all the crucial problems with Class "B".
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Well, I have my AMEC AIS Configuration display for a Class B AIS up on a screen in front of me as I write..
You are correct, class B does not let me enter my status ... ie anchored, NUC, etc.
However it does let me choose from 29 'Ship Types' ranging from '20=WIG' to '80=Tanker'.
In the middle ground lie "36=Vessel-Sailing" and "37=Vessel-pleasure craft".
Some of us ... maybe not all .. would think that differentiates between a boat that is sailing and a boat propelled by machinery....
So.. when a sailing boat stops sailing does it not become a boat propelled by machinery?
And should we not change our 36 to a 37.
Of no consequence in poor visibilty where it matters not what your ship is but if you are using your AIS for collision avoidance in good viz... instead of looking out the windows.... I think it matters rather a lot.
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27-08-2017, 04:23
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#155
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cruiser
Join Date: Nov 2007
Location: Probably in an anchorage or a boatyard..
Boat: Ebbtide 33' steel cutter
Posts: 5,030
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Re: Collision Avoidance -- Dealing with Multiple Targets
Quote:
Originally Posted by El Pinguino
In the middle ground lie "36=Vessel-Sailing" and "37=Vessel-pleasure craft".
Some of us ... maybe not all .. would think that differentiates between a boat that is sailing and a boat propelled by machinery....
So.. when a sailing boat stops sailing does it not become a boat propelled by machinery?
And should we not change our 36 to a 37.
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Cruising association says no..
Automatic Identification System (Class B) for Non-Solas Vessels | CA
Quote:
Provision is made for the main propulsion types, as follows:
36 – any vessel where the primary means of propulsion is sail.
37 – pleasure craft where the primary means of propulsion is other than sail.
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27-08-2017, 04:40
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#156
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Registered User
Join Date: Aug 2013
Location: Back in Montt.
Boat: Westerly Sealord
Posts: 8,180
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Re: Collision Avoidance -- Dealing with Multiple Targets
Quote:
Originally Posted by conachair
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Ah Ha! Immediately under that it goes on to say..
'Certain AIS B systems allow users to change and update the vessel type and activity code while underway and where these facilities exist it is strongly encouraged that the code be altered to accurately represent the vessel’s specific activity at any one time.
Example:
37 - Dive RIB transiting to a dive site;
34 - Dive RIB on site engaged in diving operations;
37 - Dive RIB transiting from dive site on completion of dive.'
So should yachts not change from 36 to 37 when they start motoring?
Mea Culpa .. Since I discovered that I had crossed the Pacific as a WIG my AIS has remained as a 36.
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27-08-2017, 06:04
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#157
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Moderator
Join Date: Mar 2009
Location: Denmark (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 33,764
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Re: Collision Avoidance -- Dealing with Multiple Targets
Quote:
Originally Posted by El Pinguino
Well, I have my AMEC AIS Configuration display for a Class B AIS up on a screen in front of me as I write..
You are correct, class B does not let me enter my status ... ie anchored, NUC, etc.
However it does let me choose from 29 'Ship Types' ranging from '20=WIG' to '80=Tanker'.
In the middle ground lie "36=Vessel-Sailing" and "37=Vessel-pleasure craft".
Some of us ... maybe not all .. would think that differentiates between a boat that is sailing and a boat propelled by machinery....
So.. when a sailing boat stops sailing does it not become a boat propelled by machinery?
And should we not change our 36 to a 37.
Of no consequence in poor visibilty where it matters not what your ship is but if you are using your AIS for collision avoidance in good viz... instead of looking out the windows.... I think it matters rather a lot.
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Well, it's a "ship type" -- not its status at the moment. So you should enter "sailing" if it has sails, and leave it there. And if you see a vessel with ship type "sailing", that doesn't mean that it's "under way; sailing". It just means that's what TYPE of vessel it is. It might not even be "under way; using power". It might be anchored, aground, moored, etc. That data field is not intended to show the present nav status; just what TYPE of vessel it is. So no, don't change it.
It's just like a vessel designated as a "F/V". That only means that it's a fishing-type vessel. Not that it's fishing at the moment.
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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27-08-2017, 13:37
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#158
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Registered User
Join Date: Aug 2013
Location: Back in Montt.
Boat: Westerly Sealord
Posts: 8,180
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Re: Collision Avoidance -- Dealing with Multiple Targets
You didn't bother to read this did you..
Automatic Identification System (Class B) for Non-Solas Vessels | CA
That is the CA view which I am sure they got from a higher authority..
If a sailing or pleasure vessel can be under either sail or power then the use of AIS for collision avoidance is not a good idea unless you have first visually identified your OoI.
How else will you know who has right of way?
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27-08-2017, 15:34
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#159
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Senior Cruiser
Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43 and OPBs
Posts: 12,888
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Re: Collision Avoidance -- Dealing with Multiple Targets
Quote:
Originally Posted by El Pinguino
You didn't bother to read this did you..
Automatic Identification System (Class B) for Non-Solas Vessels | CA
That is the CA view which I am sure they got from a higher authority..
If a sailing or pleasure vessel can be under either sail or power then the use of AIS for collision avoidance is not a good idea unless you have first visually identified your OoI.
How else will you know who has right of way?
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Simple answer. No one has right of way.
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27-08-2017, 15:46
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#160
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Registered User
Join Date: Aug 2013
Location: Back in Montt.
Boat: Westerly Sealord
Posts: 8,180
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Re: Collision Avoidance -- Dealing with Multiple Targets
Quote:
Originally Posted by StuM
Simple answer. No one has right of way.
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Please try and keep up....
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27-08-2017, 20:31
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#161
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CF Adviser
Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 10,280
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Re: Collision Avoidance -- Dealing with Multiple Targets
Quote:
Originally Posted by El Pinguino
You didn't bother to read this did you..
Automatic Identification System (Class B) for Non-Solas Vessels | CA
That is the CA view which I am sure they got from a higher authority..
If a sailing or pleasure vessel can be under either sail or power then the use of AIS for collision avoidance is not a good idea unless you have first visually identified your OoI.
How else will you know who has right of way?
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I see it differentlyv
AIS will give you the info to determine of CPA and if a risk of collision exists
When in sight of each other, daytime visuals or nightime running lights will determine if sailing/type of fishing/towing etc and determine stand on/give way hierarchy.
If not in sight due to restricted visibility..... Both vessels should be taking a proactive avoiding strategy.
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27-08-2017, 20:39
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#162
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Registered User
Join Date: Aug 2013
Location: Back in Montt.
Boat: Westerly Sealord
Posts: 8,180
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Re: Collision Avoidance -- Dealing with Multiple Targets
Quote:
Originally Posted by Pelagic
I see it differentlyv
AIS will give you the info to determine of CPA and if a risk of collision exists
When in sight of each other, daytime visuals or nightime running lights will determine if sailing/type of fishing/towing etc and determine stand on/give way hierarchy.
If not in sight due to restricted visibility..... Both vessels should be taking a proactive avoiding strategy.
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I think that is what I just said..
' the use of AIS for collision avoidance is not a good idea unless you have first visually identified your OoI.'
Sadly some hereabouts seem to think that it is OK to use AIS instead of - rather than as well as - looking out the windows.....
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27-08-2017, 20:52
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#163
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CF Adviser
Join Date: Oct 2007
Boat: Van Helleman Schooner 65ft StarGazer
Posts: 10,280
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Re: Collision Avoidance -- Dealing with Multiple Targets
Sorry my mistake, we agree on AIS avoidance function
I was thinking of the posts about improving 'type' and aspects
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28-08-2017, 03:28
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#164
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Moderator
Join Date: Mar 2009
Location: Denmark (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 33,764
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Re: Collision Avoidance -- Dealing with Multiple Targets
Quote:
Originally Posted by Kenomac
Which AIS transponder do you currently have and use?
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Si-Tex NMEA2000 black box transponder. The same circuit board is used in most black box transponders on the market; AFAIK only Vesper has their own.
But the nav status categories are from the AIS specification, not from any manufacturer.
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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28-08-2017, 03:32
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#165
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Moderator
Join Date: Mar 2009
Location: Denmark (Winter), Helsinki (Summer); Cruising the Baltic Sea this year!
Boat: Cutter-Rigged Moody 54
Posts: 33,764
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Re: Collision Avoidance -- Dealing with Multiple Targets
Quote:
Originally Posted by El Pinguino
. . . Sadly some hereabouts seem to think that it is OK to use AIS instead of - rather than as well as - looking out the windows.....
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Did anyone say that? If someone did, I didn't notice it.
Obviously, you must keep a visual watch at all times (and by hearing -- "by sight and by hearing"). It's a legal obligation as well as elementary seamanship.
AIS is a fabulous tool, but it supplements and in no way replaces either radar or eyeballs. AIS dramatically improves the accuracy of your information about the position of other vessels, and instantly does dramatically more accurate calculations of CPA and TCPA, but it is inferior to radar and eyes for figuring out whether there is something out there in the first place.
I would also mention that if I had to choose between AIS and radar, I would keep the radar.
Actually if I were forced to choose between a chart plotter and radar, I would also choose to keep the radar.
I guess that shows what an old fart I am.
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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