ARPA let's you "acquire" a target. It all sounds very military, but it's a really critical feature for navigation and collision avoidance. When you acquire a target, the radar tracks that blip on the screen, and calculates it's course and speed based on it's observed movement. It's all basic trigonometry, and a great example of how that stuff is actually useful. As one of my kid's teachers used to say, "math is everywhere".
So in the middle of the night, or in the depth of fog, you see a blip on the radar. Rather than watching the blip and trying to assess where that boat is going and what it's doing, you can acquire the target on your radar. Within a minute or so, the radar will show a vector (see, math is everywhere) indicating the target's direction and speed. Now, rather than guessing, you can see exactly where that boat is going, and how fast they are moving. This is hugely valuable, and probably hard to appreciate if you haven't tried to navigate in the fog. We've made a couple of trips from Gloucester to NYC, a trip of about 300 miles through some of the busiest waterways on the east coast, and never seen land or another boat the whole way. That wouldn't be possible without ARPA, or at least the stress level would prevent me from doing it.
The killer problem with Simrad is that their ARPA function is fundamentally broken in the current product line. We first became aware of this when we nearly got run down by a boat off the Columbia River. After that, I really started looking at this closely. The problem is that:
1) The ARPA vector does not accurately represent the boat's movement
2) The vector's direction swings around and is unstable
3) The vector's length (boat speed) is also unstable and varies widely.
The attached video shows this clearly. We are looking at a tug and barge. The tug has AIS which is a radio-based report from a boat telling you it's actual speed and course. There is no ambiguity, and no room for error. It is telling you exactly what the ship is doing. The AIS target is represented by a triangle with a line showing the course and speed of the tug. I have then created a ARPA target of the barge behind the tug, represented by a circle and arrow showing it's course and speed. The tug and tow are of course moving at the same speed and in the same direction, but the video would suggest differently. Referencing the points above, we see:
1) The ARPA course and AIS course differ significantly. They should be the same, or very close.
2) You can see that the ARPA vector swings around rather than maintaining a steady course.
3) You can see that the ARPA vector changes length by quite a bit. It should be a consistent length. representing a steady speed.
The result is ARPA that is simply not usable. I've worked through a wide range of tests and experiments with Navico support and engineering, and the installation has been scrutinized every way to Sunday and passed with flying colors. Engineering finally reproduced what I have been seeing and agreed there was a problem they needed to fix. This impacts both my radars (4G and 10kw open array), and based on reports from other Simrad owners, appears to be a long standing problem that has gone unnoticed until now.
As part of testing, one thing Navico asked me to do was to acquire the same target multiple times. They wanted to see whether there was any difference between the different targets. The next video shows this. I acquired the target three times, and you can see that two of the vectors are mostly in lock step with each other, but the other is pointing off in a different direction. And all three wander around.
Over on the right side of the screen you see a bunch of data boxes, include 3-4 larger ones showing various AIS targets. My understanding is that these are supposed to be the closest target. But you can see that there is no data in the data boxes. You see a ships name in one case, and just the MMSI (ship's number) in the others, but there is no course or speed info, and no computed CPA (closest point of approach), or TCPA (time to closest point of approach). If I look up these ships on Coastal Explorer (it also receives and displays the AIS data), all the info is there just as it should be. So the receiver is working and the data is available, but the radar is not displaying it properly. The targets plot correctly on the screen, but the data boxes are not filled in, and the CPA and TCPA is only occasionally calculated.
|Missing AIS info|
The radar incorrectly reports the operational hours on the Magnetron. A Magnetron is the part of the radar that generates the ping used to find targets. It's the Flux-Capacitor for a radar, and it has a limited life span. They are good for a few thousand hours, but when their time comes they need to be replaced. So all radars have a built-in hour meter to keep track of this.
The Simrad 10kw radar reports a seemingly random number of operational hours. The first time I looked, it reported 26,000 hours and I thought I had been sold a used radar. But the next time it reported a very small number. Simrad confirmed it's reporting garbage info. I don't know how to maintain a radar under such circumstances. I guess I need to buy an egg timer.
Simrad advertises a feature whereby you can tell the open array what angle you want it to park at. Most radars just stop where they stop, and this little feature was really interesting to me since it allows the radar to be parked where it doesn't shade my solar panels. But despite numerous attempts to park the array in a predictable manner, I called Simrad tech support. They told me that the feature didn't work. Worse yet, they know it's not possible for it to ever work. The radar has no brake, so they have no way to control where it stops. WTF? Talk about false advertizing. Wow.
This one is related to the park angle that doesn't work and can never work, so it's kinda moot, but it's reflective of the overall disregard for product testing before releasing it for sale. You can go into the radar menus on the NSO and program in the angle where you want to array to park. But when you turn the radar off, it forgets the angle that you programmed in. So you need to reprogram it very time you shut down the radar.
Problem # 6:
This is another ARPA problem. If you lock onto a target, then shut off the autopilot, the ARPA vector swerves off about 90 deg from the actual course of the target. These two systems should have nothing to do with each other. Why turning off the AP impacts ARPA is beyond me, but it does. A friend tried the same experiment on his Simrad equipped boat and got the same results.
I think Apple needs to start building Marine navigation gear! Love the blog and your technical testing! This should be shared with the folks at Panbo!!ReplyDelete
I feel your pain and frustration Peter.ReplyDelete
I applaud your documentation of the faults exposing Simrads's blatant false advertising and their in excusable negligence in marketing a dangerous and grossely immature product
To prob # 2:
If you completely turn off your Coastal Explorer, where it shows all AIS-data, will it then show the AIS-data on the radar screen?
i.o.w.: maybe it does not share the info once they are reported to (already used for) an other device?
This egg timer should be given to you and all other customers for free by Simrad. Great marketing idea: Buy one radar and get one egg timer for free!
Pleasure to read how accurately and deeply you go into it.
What systems do commercial ships use? Do they use and rely on ARPA?
Jochen Brecht, Hamburg, Germany
P.S. Any other issues than electronics on your boat?
Any failures of any pumps or vans, any leaks of hydraulics, oil, water, or anything to report?
What is your temperature inside the ER while underway?
And do you have data already for your fuel consumption at different speeds?
Highly interesting to me how reliable all systems are and how much of caretaking they need.
Thanks for the comments.
Regarding the AIS, the vessel position reports are broadcast on the N2K network for all to hear. This is how most all N2K data is transmitted, and hence there is no notion of it being consumed by one device, and hence not available to another. It's like listening to an announcement in the airport. Everyone and anyone can listen, and pay attention as they choose.
As for other issues, that's a really good question. I was just commenting to my wife the other day about how distracting all these electronics problems have been from getting other things done on the boat. But in general things are working well.
Sorry, I didn't answer your question about commercial ships. They are all regulated by international agreements, and largely regulated by IMO regulations based on ship size, etc. ARPA is required functionality on larger commercial ships, and devices have to be IMO certified. Needless to say, the Simrad gear is NOT IMO certified.ReplyDelete
Recreational boating is largely free from any regulation. In many jurisdictions there is absolutely no training requirement whatsoever. I personally think this is wrong since untrained boaters place other people in danger. If you are going to fuck with my life, you should need a license to do it.
Peter, just wanted to put in a good word too--buck up bro'. I've been following you for a while now, I really appreciate how clearly you describe and explain things for the 'common mariner'.ReplyDelete
I was getting ready to go basically the same route for radar and some of your other gear you had gone, but now obviously won't be. We await all your blog entries with real anticipation. Thanks, Wil
Thanks Wil, I appreciate the support. But really no sympathy is needed. If I can save others the same pain then it will have been worth it.ReplyDelete
Hopefully we can start making our expectations clearer to manufacturers. It's unfortunate that our purchases are the only means of communications.
I think customer reviews and feedback are one of the greatest benefits of the internet, and we should all use it to our greatest advantage. Vendors can't hide their crap anymore. It's hanging out there for everyone to see.
I appreciate all the detailed analysis you go through and explain so clearly for all of us to read.
I am selected the B&G 4G radar (sailboat) as the best replacement for my aging Koden but reading the problems you discovered I am wondering if I should wait for 5G radars?
Thanks for your reply.
s/v Rajah Laut
I think a lot depends on whether you use or care about ARPA. It's pretty clear than most people don't. I found a Simrad ARPA tutorial video on YouTube that exhibits the same wandering vector as my radar, so this problem has been in the product line for 3 years or so and nobody seems to know or care.ReplyDelete
But setting ARPA aside, I still think the 4G's general performance is not as good as a 4kw dome radar. I've had both, and am going back to a regular dome radar. There were just too many things that the 4G didn't pick up that it should have, like a 30M tug boat about 2 miles away.
Thank you for your quick response. I have always been to use all the features of a radar. I am a pilot also and have taken radar training. I had MARPA on some older Raymarine radar on a previous boat. Although having to manually select my targets is work, it also has it's advantages. I have not had the joy of working with AIS plus (M)ARPA on an overlay screen so I guess anything would be better than what I have now.
Getting back to jets where things happen real fast boating is relatively relaxing where there is usually ample time to analyze the situation without the need for gut reaction.
Of course a long ocean passage can be marred by a lousy docking but the best radars in the world probably will not help much in that situation.
Thanks again and good luck with your quest.
Have been reading about your experiences with great interest as it is very detailed and focused on detailed knowledge about your boat whoch I think is critical for safe boating. I have a question regarding the Furuno TZT and their radar as I have the 12kW open and in the manual it states that you can use relative motion in the prediction but what is not available is AIS/ARPA target trails. Need to check about AIS/ARPA relative motion prediction when I go out next week. As a side note, I switched from Raymarine last year and clearly very satisfied up to now. I use Maxsea heavily for fishing and for me one significant benefit has been using Maxsea as additional work stations with marine monitors, keyboards and mouse. The integration woth the TZT is complete including AIS/ARPA target tracking and I believe it will work with your radar as a repeater.
Thabks again for sharing your experiences, Rolando
I'm not sure if you have read this post http://www.mvtanglewood.com/2015/02/radar-comparison.html
It compares the features of a number of radar devices, including those for the TZT. I believe it's accurate, but let me know if you find any errors. I just took a look to refresh my memory, and from my research the TZT radars can display relative or true Echo Trails, but the prediction vectors are True only, and there is no support for Track History.
Note the difference between Echo Trails and a Track History. For me it took a while for the difference to really sink in. Echo Trails are for ALL returns - everything. Land, buoys, other boats, birds, rain storms, etc will all slowly smear across the screen. If there is a lot on screen it will quickly become unreadable and you need to reset/restart the trails.
Track History, on the other hand, is only kept for ARPA and/or AIS targets, so they don't clutter up the screen and don't cause land masses to smear. It's just a clean dot dot dot track just like your own boat's track if you have than enebled in your TZT.
Hope that helps,
Thanks for quick reply. I have read the radar comparison post as well as most of your postings, great read! I think that the way I am reading the TZT manual the AIS targets will show COG vectors for targets bot only based on time. They will not show history. You are correct, echo trails smear the screen fast and I stopped using it a long time ago. You are far more experienced with radar than I am as I had not really looked at the relative motion option, yet it sounds very appealing for some situations, even when looking for birds when fishing.
I want to check how how/if ARPA/AIS target tracking works with Maxsea as I already found some options available in the Maxsea sounder module that are not availabe in the TZT. In fact, my Maxsea manual says that you can activate tracks for AIS targets in a targets layer. Have to check to see if my version has it and, if it does, try and see how it works.
Interesting, but you are comparing two different technologies. AIS data is received from a vessel based on the vessel's own supplied data e.g. COG from GPS system, it therefore uses historical COG and extends this to show future COG, assuming the vessel is continuing this courseReplyDelete
MARPA is using a radar to look at a target. It gets returns from this target and can then see the direction the vessel is going and the changing range. From this it can calculate GOG and speed.
However, the radar can only do this if it is on a stable platform fixed in space, obviously if it is on a boat, it is not on a stable platform. The heading of the boat that the radar is mounted is changing, so the radar needs to know which way it is pointing.
A fluxgate compass feeding in heading (HDG) data to the radar will allow the radar to calculate the heading of its own boat, together with the angle that the radar calculates the target to be at, will give the true angle of the target. If the compass data is not updated quickly enough, the angle will change rapidly and so will calculated COG. This will cause the information in graphical form to be changed on the screen. The faster the update time of the compass, in Hertz, the better and more stable the graphical representation of the target will be.
Try doing the same experiment with the boat tied to the dock and not moving to see what happens.
I think your assessment is correct both in the differences between the two tracking methods, and the requirements for a good heading input for proper ARPA operation. (I'll just say ARPA, but it covers MARPA as well). Every radar I have worked with requires a 10hz heading input for proper ARPA operation.
When I was diagnosing the problem with Simrad's New Zealand Radar engineering tear, we went through a number of steps to eliminate external causes, including the two your bring up (sea state and heading accuracy). At first they though the problem was my heading source, or possibly the fact that I had a primary (HS70 sat compass) and secondary (RC42 rate compass) heading source on the boat. Source selection was shown to be working correctly, and the problem was reproducible with only one of the compasses on the network. We even stripped the network down to just the NSO, Radar, and HS70 to eliminate all other N2K interactions. Oh, and both compasses supply heading at 10hz as required for ARPA.
I was also able to reproduce the problem while at anchor in dead calm water, so only one of the two vessels was moving. Last, in the video in this post we were in dead calm water with both boats on steady courses.
Between AIS and ARPA, I would rank Class A AIS as more accurate than ARPA. Class B AIS is just as accurate when it updates, but you need to keep in mind that it only updates every 30 seconds so the boat position reports are spaced further apart. The point of comparing was to see how close ARPA comes to AIS, and you can see the results with the Simrad radar. In contrast, all the Furuno radars that I have used provide an ARPA track that very closely matches the AIS track (heading within a few degrees, and speed within a few tenths of a knot). I haven't had the opportunity to compare with Raymarine or Garmin, so can't speak to how well they work.
Yes, I saw that post on SetSail. There was some overlap in the issues we encountered, but I dumped my Simrad gear before I used it long enough to run into the other issues Steve Dashew reported. I'm only sorry to see them go through the same thing I did, and now be faced with replacing it all with something else.ReplyDelete
There is an alternative to get reliable MARPA and ARPA target detection and tracking from an Simrad / Navico radar. Recently we released the Navico Radar plugin 3.0 for OpenCPN (br24radar_pi). This plugin for OpenCPN (running on Mac, Linux and Windows) currently supports the older BR24 radar, the 3G and the 4G. The plugin provides most features you expect from radar software, such as:ReplyDelete
- adjustable offset of radar position from GPS
- both true and relative trails
- radar on chart overlay
- two independent radar-only windows in various orientations
- guard-zones with automatic target detection for ARPA
- target tracking for up to 100 targets per radar
Once targets are followed they are handled as AIS targets, including the various alarm function based on CPA and time to CPA.
Currently there is also a beta version for the Simrad Halo radar, to be integrated in the next release.
Of course the radar software requires a heading source. In practice a heading that is updates 1* per second works well, but faster is better. More info on http://www.cruisersforum.com/forums/f134/navico-radar-plugin-v3-0-released-191536.html