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Old 09-05-2015, 04:07   #1
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CPA and TCPA of RADAR targets not equipped with AIS

Hi,
I have an AIS trasponder class B onboard connected to my laptop so I can have CPA and TCPA of any vessel equipped with AIS. I also have an old Furuno Radar 1721 which works perfectly but assessing whether a risk of collision exists with targets that do not have AIS and only show up on the radar is a not-so-easy and time-consuming exercise.
Can anyone please advice on whether I could upgrade the radar (keeping the same aerial) so as to have quickly the CPA and TCPA of any target ?

Thanks a lot.
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Old 09-05-2015, 14:06   #2
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Re: CPA and TCPA of RADAR targets not equipped with AIS

What you are looking for is ARPA or MARPA. This feature let's you lock onto a target and the radar automatically tracks it, calculating CPA and TCPA along the way.

I don't know about the 1721 specifically, but many of the Furuno radars can accept an optional ARPA boat that adds the feature. I'd suggest checking Furuno's web site, downloading and reading teh installation manual for the 1721, and calling or emailing them directly to ask is an ARPA board is available for that model, or what other options might be available.
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Old 10-05-2015, 12:57   #3
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Re: CPA and TCPA of RADAR targets not equipped with AIS

Alby,
The short answer is, no, there is no way to economically "add" ARPA using your existing radar scanner ("aerial")...but, you can use the "Plotting" feature of your existing Furuno 1721, and/or do some easy/quick calculations, to do the same thing....(see pages 2-19 ad 3-11, 3-12, of the Furuno 1721 manual, for details...)
https://www.furunousa.com/ProductDoc...s%20Manual.pdf


Also, since the typical lifespan of a radar magnetron (the transmitter tube in the radar scanner, that makes the thing work) is about 3000 hours....
And, since the Furuno 1721 is a 1994 series radar (and the Mk2 coming about 6 - 7 years later?), this means that if your radar has had an average of 3 hours use per week, for the past 15 - 20 years, your 1721 is at or near its useful life...
(You can read the total number of hours on your radar from the "installation screen")
So, if your 1721 is close to that 3000 hours, the answer of whether or not you could still use your old radar scanner or not, becomes moot!

Quote:
Originally Posted by Alby1714 View Post
I have an AIS trasponder class B onboard connected to my laptop so I can have CPA and TCPA of any vessel equipped with AIS. I also have an old Furuno Radar 1721 which works perfectly but assessing whether a risk of collision exists with targets that do not have AIS and only show up on the radar is a not-so-easy and time-consuming exercise.
Can anyone please advice on whether I could upgrade the radar (keeping the same aerial) so as to have quickly the CPA and TCPA of any target ?
1) In order to have a CPA and TCPA (of radar targets) calculated for you and displayed on a screen for your use, you'd need a radar unit that can track multiple targets and calculate these points of approach, etc., which in radar parlance is call "ARPA" or "MARPA" (Automatic Radar Plotting Aid or Mini Automatic Radar Plotting Aid)...
2) Yes, there are some analog (non-digital, non-"HD") radars, like your old Furuno 1721 radar, that do have APRA or MARPA capabilities or options (such as the Furuno 1835)....but they aren't cheap...
3) Most modern small-boat radars are now "digital", meaning that the signal coming from the radar scanner ("aerial") is digital not analog, and as such your older Furuno 1721 scanner ("aerial") is not compatible with them...


So, while you "might" be able to find a radar display / processor that has ARPA capability, that would be compatible with your older 1721 (you'd need to talk directly with Furuno tech support about this specifically), it would be cheaper to buy a newer, modern "digital" compatible radar unit and scanner (and this would also be a daylight viewable LCD display), that has MARPA / ARPA (as well as other modern features, such as AIS display, etc..)



I hope this helps...

Fair winds...

John
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Old 10-05-2015, 13:39   #4
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Re: CPA and TCPA of RADAR targets not equipped with AIS

John,
thank you very much. Your explanation was very clear and comprehensive.
Alberto
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Old 10-05-2015, 22:21   #5
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Re: CPA and TCPA of RADAR targets not equipped with AIS

I have never found MARPA on recreational radars to be all that useful. But the old-fashioned EBL is a killer app for collision avoidance. With the caveat that you can only do one target at a time (or four, in the case of radars like my Simrad 4G). The reason why the EBL is so good for this is that unlike MARPA, which gives a frequently updated calculated value, the EBL show you a long term cumulative average bearing. Since recreational radars have poor bearing accuracy in general, due to large beamwidth and short antenna base , and get typically poor heading data, the instantaneous computed value can't be all that good. But. The EBL averages all this out and gives you a vivid graphical picture of a developing collision. Other downside is the EBL doesn't explain late course changes very well.

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Old 11-05-2015, 07:36   #6
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Re: CPA and TCPA of RADAR targets not equipped with AIS

Quote:
Originally Posted by Dockhead View Post
I have never found MARPA on recreational radars to be all that useful. But the old-fashioned EBL is a killer app for collision avoidance. With the caveat that you can only do one target at a time (or four, in the case of radars like my Simrad 4G). The reason why the EBL is so good for this is that unlike MARPA, which gives a frequently updated calculated value, the EBL show you a long term cumulative average bearing. Since recreational radars have poor bearing accuracy in general, due to large beamwidth and short antenna base , and get typically poor heading data, the instantaneous computed value can't be all that good. But. The EBL averages all this out and gives you a vivid graphical picture of a developing collision. Other downside is the EBL doesn't explain late course changes very well.

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Dockhead, you ever get that GPS compass you considered a few months ago? Has the improved heading data helped with the MARPA?


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Old 11-05-2015, 13:07   #7
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Re: CPA and TCPA of RADAR targets not equipped with AIS

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Originally Posted by Dockhead View Post
I have never found MARPA on recreational radars to be all that useful. But the old-fashioned EBL is a killer app for collision avoidance. With the caveat that you can only do one target at a time (or four, in the case of radars like my Simrad 4G). The reason why the EBL is so good for this is that unlike MARPA, which gives a frequently updated calculated value, the EBL show you a long term cumulative average bearing. Since recreational radars have poor bearing accuracy in general, due to large beamwidth and short antenna base , and get typically poor heading data, the instantaneous computed value can't be all that good. But. The EBL averages all this out and gives you a vivid graphical picture of a developing collision. Other downside is the EBL doesn't explain late course changes very well.

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This is certainly true with Simrad's MARPA, but not true at all with Furuno's. I can't speak for Raymarine and Garmin. I once thought all MARPA was created equal among the major vendors, but it couldn't be further from the truth. Since I only have experience with Furuno and Simrad, and can't say whether Furuno's performance is head and shoulders above everyone else, or if Simrad/Navico is the poor, third step child for failed high school math.

What I can say with confidence is that Furuno's MARAP (actually, ARPA) works very well based on first hand use of three different models of radar.

And I can say with equal confidence that Simrad's MARAP is for all intents and purposed useless based on first hand use of two different models of radar.

In all the above cases I've run the MARPA/ARPA with an RC42 rate compass and with an expensive Sat Compass. The results are the same in all important ways.

Bottom line, in my opinion..... MAPRA isn't useless - just the opposite. I think it's one of the best parts about radar. What's useless is Simrad's MARPA.
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Old 11-05-2015, 14:35   #8
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Re: CPA and TCPA of RADAR targets not equipped with AIS

Tanglewood,
Well, I can speak good things about Raymarine's MARPA (at least my experience with the E-120/E-80, w/ 24"/4KW radome)....
As long as you have a fast heading sensor input into the E-series units, the MARPA function works great...
(FYI, the "fast heading data", from the sensor going to the autopilot corepak, is NOT put onto the SeaTalk bus, from the autopilot....no, that would make sense and we know that can't happen....
Regular heading data is of course on the SeaTalk bus, but not the "fast heading data"...
But, the fast heading data IS output from the S3G corepak via NMEA 0183....so you need to have a NMEA 0183 connection from the corepak to the E-series, in order for tha MARPA to work well...
Without this NMEA 0183 connection, MARPA works....but has some occasional issues....
With the NMEA connection, I find MARPA to work very well!)
Quote:
Originally Posted by tanglewood View Post
I can't speak for Raymarine and Garmin. I once thought all MARPA was created equal among the major vendors, but it couldn't be further from the truth. Since I only have experience with Furuno and Simrad, and can't say whether Furuno's performance is head and shoulders above everyone else, or if Simrad/Navico is the poor, third step child for failed high school math.

What I can say with confidence is that Furuno's MARAP (actually, ARPA) works very well based on first hand use of three different models of radar.
I hope this helps some...

Fair winds..

John
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Old 11-05-2015, 18:37   #9
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Re: CPA and TCPA of RADAR targets not equipped with AIS

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As long as you have a fast heading sensor input into the E-series units, the MARPA function works great...
Without this NMEA 0183 connection, MARPA works....but has some occasional issues....
With the NMEA connection, I find MARPA to work very well!)
I second that. Without fast heading sensor input the Raymarine MARPA is pants, and unsurprisingly so. In a sailing yacht at sea the heading is all over the place and it's quite reasonable that it will loose lock on the targets. This can happen especially in rough conditions anyway. Without a fast heading sensor you'll soon give up on MARPA due to all the lost target alarms, and ridiculous speed heading readouts.

Even with MARPA you still have to select the targets so it's still not an AIS type experience.

No radar is really going to give you the same convenience of operation as AIS. As the OP suggested use the EBL, VRM, to quickly see what's happening on the old school radars.. Use a lolipop stick as low tec EBL marker

As a radio engineer who grew up with magnetrons and klystrons don't worry your radar isn't just going to stop working one day when the hours counter hits the stops. More likely you'll notice a decrease in performance, you find that your having to wind up the gain more than in the past etc.. You can also check the magnetron voltage on these units, the details are in the manual.

These little Furuno radars when properly tuned up give a pic superior to many of the more modern ones with their dummed down interfaces and software trying to compensate for crappy RF design. They do require more investment in learning how they work and practising with the controls and finding what settings work.

Chris
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Old 12-05-2015, 15:04   #10
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Re: CPA and TCPA of RADAR targets not equipped with AIS

Thanks Chris for pointing out that the decay of the magnetron is slow and not abrupt (it would have been my next question !) and that the old fashion radars still have some value.
Alberto
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Old 12-05-2015, 16:36   #11
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Re: CPA and TCPA of RADAR targets not equipped with AIS

Yes, of course Chris is correct....
I wasn't trying to say that your radar is on its last legs!!

Just that spending the time and money in changing out to a new display (if Furuno made one the worked with your old scanner), might be an economical mistake if your radar has been used a lot / has many, many hours on it...in the vein of how much to spend for how much results, it was just one criteria that you can use to make your decision...
Quote:
Originally Posted by Alby1714 View Post
Thanks Chris for pointing out that the decay of the magnetron is slow and not abrupt (it would have been my next question !) and that the old fashion radars still have some value.
Alberto
BTW, even with manual tuning, and finessing the controls on an older unit, etc., it is amazing how well a "new" modern radar works compared to an older unit....(I've upgraded a couple times in the past few decades, and while my old existing radars were working fine, the new radars and displays always seem to be a significant step forward!)

Just my experience...

I hope this helps...

John
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Old 14-05-2015, 19:52   #12
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Re: CPA and TCPA of RADAR targets not equipped with AIS

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Originally Posted by Littlechay View Post
Even with MARPA you still have to select the targets so it's still not an AIS type experience.
Current Furuno ARPA implementation will automatically acquire and track up to 30 targets.

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Old 14-05-2015, 21:35   #13
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Re: CPA and TCPA of RADAR targets not equipped with AIS

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Current Furuno ARPA implementation will automatically acquire and track up to 30 targets.

Mark
Interesting but is it ARPA or MARPA? makes quite a difference especially to the weight of ones wallet.
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Old 14-05-2015, 21:43   #14
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Re: CPA and TCPA of RADAR targets not equipped with AIS

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Interesting but is it ARPA or MARPA? makes quite a difference especially to the weight of ones wallet.
The Furuno gear is all ARPA. But the only difference that I can find between ARPA and MARPA is that ARPA can automatically acquire targets in a given zone, where with MARPA you need to select each target that you want to acquire. And MARPA typically supports fewer targets. 10 seems to be pretty common. The low/mid range Furuno stuff is 30 targets, and their high-end radars are 100 targets.
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Old 14-05-2015, 21:50   #15
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Re: CPA and TCPA of RADAR targets not equipped with AIS

Oh, and I don't think the Furuno radars are any more expensive than the equivalent for other vendors. They all seem pretty competitively priced. But you get automatic target acquisition if that matters to you, and support for more targets.

For what it's worth, I prefer to acquire targets manually, and don't think I've ever had more than 10 on the screen. So I wouldn't get too hung up on ARPA vs MARPA or 10 vs 30 targets.

But what DOES matter is how well the ARPA/MARPA works, and Simrad's sucks big time.
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