AIS INSTEAD of radar?

[mako]

Something that I have experienced for a couple of years... having AIS makes you less of an unknown, and therefore less of a potential security risk. It completely eliminated the constant “visits” by security forces and coast guard here in the Persian Gulf.

[Hoodsail]

It has been helpful in reading thru the responses to determine whether i will add radar to my AIS...currently for me weather is the only applicable reason...i heave to outside of unfamiliar harbors at nite. My send/receive AIS displayed on my chartplotter enables me to "see" traffic, albeit only for those with transponders. Has helped me to hail commercial boats, although many dont answer. And helped with separation in fog in long island sound.
Boat has other needs where $ will be better spent. thnks

[Pelagic]

Originally Posted by Uricanejack

I am still convinced Elpingo is right.

I’ve tried to explain why before but I’m not articulate enough to explain it. But here goes anyway.

The radar pictures are not distorted. They are two different displays. The first is relative motion. The second true motion.

The first is simple easy to understand the second takes a little bit of thought
In this particular situation.
Some people find a crossing situation with relative motion hard to visualize.

The problem with using ground track rather than water track doesn’t effect relative motion. The relative motion will be unaffected.

Most of our little radars (mine furuno 1612) are relative motion heads up displays. Without a high quality log and a gyro compas. Stabilizing a radar without these is can be done with GPS, but it will be ground stabilized.

The true motion is then calculated. But using ground speed not water speed distorts the true motion. The true heading is not the true heading and speed through the water. it’s the course and speed made good.

In the case illustrated on the two pictures. The true display appears to have a heading 40 degrees from the true heading the vessel is steering.

This picture could possibly be miss interperated as a crossing situation when it is actually a head on situation.

This might not be a problem in good visability. Your eyes will tell you what’s happening. If you look. We see the world relative to us.

The EBL or heading line will confirm the relative motion.

Most people will find this difficult to resolve in thier mind if they can’t see the other vessel.
An experienced radar plotter should resolve it quite quickly.

Problem? Expierienced Radar plotters are getting old and retiring. I would be very surprised to see or hear of systematic radar plotting being carried out on a ship today other than as a class room excessive.

The auto matic aids have taken over and nobody makes radars with reflection plotters.

The lecturer is correct like to like can be compared. Or are comparable.
So ground to ground true motion will give a over the ground correct result with the correct CPA.

The ARPA can’t compare ground to ground. The ground stabilized ARPA. Is observing the movement through the water not over the ground.

The relative motion is unaffected. It is accurate. The problem is by applying the co and speed over the ground the calculated true motion is incorrect. So the ARPA will give the correct CPA, with the wrong heading and course displayed.
The displayed true motion will be incorrect.

I expect for a number of reasons most ships will have thier ARPA set up in this mode.
My opinion it’s not a big problem if the operator understands thier is an unknown error in the true motion information they are using for colision avoidance.
In most circumstances it will be a small error.
In this example it’s an unusual large cross current being used to illustrate a point. This big an error will be rare in practice. It can happen.

By using ground to ground. AIS. The problem is reversed your true motion is accurate. Over the ground. Because they are comparing like to like. Current leeway are not a factor in determining CPA.

The problem is to determin the relative motion. To take the steady bearing and put your EBL on the other vessel. Which is in a virtual world not an observed world.
The relative motion has to be calculated. But something is missing from the algorithm.
Again the calculated aspect will be incorrect. Which in some circumstances will not matter.
In some particularly head on or nearly head on or border line overtaking crossing.
This could be misleading.

So you will get correct CPA with incorrect course and speed.

Is it a big problem? Like any error, Not if you know it’s there. You can make an allowance.

The author of the articles mentions big oil audits. I have never seen a big oil audit. So I wouldn’t know what they look for. They have a list with boxes to check. Apparently the ARPA setting is one of them.
The author doesn’t agree with.

Like I said my opinion. Elpingo is right. Water track should be used for colision avoidance.
If not so long as you know the difference. It’s ok.

I could confuse someone trying to resolve the difference in a relative display and a true display. Eg a relative radar and a true plotter.

Great summary and as an asside I remember the early simulator two week course modules with reflecting plotters and any size ship or location.

By the second module, more targets, more current, narrower channels and more traps if you deviated from approved procedures.

They still would not let us use ARPA so it was stressful.

I remember asking the Instructor WHEN to use True Motion Stabilized vs Relative North Up! (Dockhead we were taught to stay on N-up because of parallel indexing navigation)

Instructor explained TM was used more in close quarter situations with curving routes like a Chanel estuary. You could faster appreciate Target course changes, confirm visual Aspects but it took an experienced operator to keep the relative courses updated, by switching back and forth between presentations.

Of course ARPA now gives you that CPA regardless of TM or RM..but in the days of plotting by hand, it was a challenge.

I found TM to be very useful in places like the Seto Naikai (inland sea) where you have high density traffic joining/departing the mainstream via the many channels. TM alerted you to the change much quicker.

[fish53]

Originally Posted by Hoodsail

It has been helpful in reading thru the responses to determine whether i will add radar to my AIS...currently for me weather is the only applicable reason...i heave to outside of unfamiliar harbors at nite. My send/receive AIS displayed on my chartplotter enables me to "see" traffic, albeit only for those with transponders. Has helped me to hail commercial boats, although many dont answer. And helped with separation in fog in long island sound.
Boat has other needs where $ will be better spent. thnks

With a plotting radar it can tell you the position of a target and you call asking for the vessel in that location, it's done by commercial vessels frequently. AIS only adds some to situational awareness when radar expands it significantly.

[daletournier]

I haven't read the whole thread therefore maybe repeating something that's already been said.

Radar no longer needs to be expensive due to opencpn. I rarely used my old raytheon for a variety of reasons but in recent times I've had crew fall a sleep on watch, this got me reviewing my radar Ais setup. I'm a big fan of Ais.

I've just fitted a B&G 3g radar, it cost me $1,100usd. As of yesterday it's operating on my PC using opencpn. I just think it's incredibly cool that I now have Ais and radar over laided on a chart on my PC for such little money.

The combination of Ais and radar alarms really creates a very thorough crew on watch.

There's lots of vessels in poorer countries that do not have Ais. For $1,100 I now have a very modern radar that draws very little and works alongside my Ais.... what's not to like.

[mako]

Originally Posted by daletournier

I've just fitted a B&G 3g radar, it cost me $1,100usd. As of yesterday it's operating on my PC using opencpn. I just think it's incredibly cool that I now have Ais and radar over laided on a chart on my PC for such little money.

The combination of Ais and radar alarms really creates a very thorough crew on watch.

I really like this idea. I was always a bit nervous out at sea for days while sleeping in my cabin at night with others taking watch, especially less experienced friends or family. It would give some nice comfort to have an iPad repeater showing the radar image, sitting next to my berth.

[Dockhead]

Originally Posted by makobuilders

I really like this idea. I was always a bit nervous out at sea for days while sleeping in my cabin at night with others taking watch, especially less experienced friends or family. It would give some nice comfort to have an iPad repeater showing the radar image, sitting next to my berth.

I agree that effective radar and AIS alarms enormously enhance watchkeeping offshore. The FMCW radars, at least the 4G ones (no experience with the 3G but suppose it's similar), have superb DSP which makes the alarms very effective -- very few false ones, and very few missed targets.


And it's great to have the display at your bunk when you're off watch and not entirely sure of the quality of the watch on deck.


However, I would caution everyone to regard that as equivalent to "a watch on deck", by itself. The alarms are not infallible, even in good weather.


I had a scary moment last summer coming back from the Arctic, just passing Petershead in Scotland at 4 AM or something after three days and nights on passage from the Faroe Islands. I was on watch myself, and I was alert and in the cockpit, and all the alarms were set. I jumped when the VHF crackled with a hail to my boat name. Turns out, both I and all my alarms had failed to detect a fishing boat coming into to Petershead, which was now less than a mile off and on a collision course.


The day was saved by the fisherman's having seen me on AIS. But he couldn't recognize my nav lights (I was using tricolor). He had receive-only AIS so I was not getting data from him, and he somehow slipped through my radar guard zone, and I failed to see him visually, although the weather was not too bad (some sea running but not too rough). He called me, I turned on deck lights, we saw each other, and disengaged. I thanked him profusely for being so alert.



That was a big bloody fail of watchkeeping on my part I'm glad it was me and not one of my crew -- I'd have made crew walk the plank for that.



I'm telling all this to suggest not being to complacent about radar and AIS alarms substituting for a diligent human watchkeeper.

[Dockhead]

Originally Posted by Hoodsail

It has been helpful in reading thru the responses to determine whether i will add radar to my AIS...currently for me weather is the only applicable reason...i heave to outside of unfamiliar harbors at nite. My send/receive AIS displayed on my chartplotter enables me to "see" traffic, albeit only for those with transponders. Has helped me to hail commercial boats, although many dont answer. And helped with separation in fog in long island sound.
Boat has other needs where $ will be better spent. thnks

Only you can decide, but if you're sailing in traffic, and especially, in fog , AIS is giving you a false sense of security. AIS does not "see" anything -- this is the wrong way to look at what you get from AIS -- AIS only reports what it passively receives from vessels with working AIS transponders, and which have them switched on. Radar, on the contrary sees. It is active, not passive, and does not require any transmissions from other vessels, and it sees not only vessels, but other objects. That is "seeing".

[RUSTYNAIL]

Dockhead... There is nothing better than real life experiences to support this run of great feedback. Thanks, What radar do you have, and is it one that requires manual tuning, you mentioned experience with 4G. I'm so impressed with the Simrad 4G which comes in different company names. I'm too old to deal with tuning and this unit works well for me. I feel comfortable when I set alarms. I sure don't travel like you, and my last trip to the arctic was in a steel icebreaker in74. In the US. the commercial fishermen by law are required to have a radar reflector if their vessel can't be seen on radar less than 6 nm's. That doesn't mean they all have them all of the time. I'm a safety nut and you can learn more about me on the internet if you search "greg johnson EPIRB".

[JSSailem]

I think it is a matter of where and how you cruise/sail.

If your a daysailer and prefer to sail in closed waters on bright sunny days, then either AIS/Radar or both on the boat are just Bling.

You sail in marginal weather among larger and faster boats, through narrow passages or open waters that require you to navigate narrow passages then you likely have a need for both tools.

These are tools. You also need to understand their strengths and weaknesses which only comes with training. Training with all of your tools for safe passages.

Experience has given me proof that these are both valuable tools. Sailing 3 weeks ago in a snowstorm approaching a narrow passage between islands in BC, we got a call from the BC ferry on the other side of the island. Captain called us by boat name and wanted to know our intentions as in the next 15 minutes we were about to both round the islands and enter the passage between from opposite directions. The AIS let him know who we we're and to make the VHF communication personal. We were planning a Southern turn in the passage, the BC ferry was planning a Northern turn. The whole communication took less than 2 minutes. We agreed that best passage would have us avoiding each other if we passed starboard to starboard. We both avoided the rocks and made successful passage. He came up on radar as we were turned into the passage. In this case AIS and VHF radar made the event a safe meeting. Radar confirmed the situational awareness once it came into play. You can not see a Radar signal when the target is behind an island. But when he became visible to radar, we could affirm that our passage would be Starboard to Starboard and no conflicting course. He was a big grey mass in the minimal visibility when we were about 50 yards apart and disappeared as quickly as he appeared.

In another experience AIS /Radar and Radio all were useless. An active Fog watch enabled avoidance of death or sinking from a fishing boat speeding through water with only 75 yard visibility.

You need all the tools possible to safely navigate in less than perfect conditions.

[Yellow bird]

Originally Posted by callistov42

My old Autohelm radar finally died. One of the electronics guys I was talking to suggested that if I installed AIS I really didn't need to replace the radar. The fact is that I almost never used my radar unless I was closing on a coast or looking for a reef. Another friend who’s boat is in New Zealand is really enthusiastic about the Vesper Marine “smart AIS”. I plan on putting a Raymarine MFD in the cockpit at the helm station (I already have one below at the nav station) that will repeat the chart and display the AIS information. Any comments about the need for both radar and AIS?

I absolutely agree with almost everyone, radar and AIS are not interchangeable but complementary,
I recommend both, but if I had to choose, I would choose radar

But let me tell you something more that nobody says (or at least it seems to me),
never forget, neither can replace a man on watch.

Many accidents/collisions are caused by lowering of attention (or worse complete absence of man on watch) due to the false sense of safety given by the instruments.