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Saturday, February 7, 2015

Radar comparison

I was asked for more detail on which radar I plan to use in Electronics 2.0, and about the differences between some of the radar models available.  This chart shows a feature comparison between radars focused on the key navigation features.  Note that all radars that I've ever encountered have Electronic Bearing Lines (ELB), and Variable Range Markers (VRM), so I haven't included them in the chart.

The issue with Simrad, by the way, is that the ARPA/MARPA heading vector is erratic.  Sometimes it's stable, but other times the heading swings all over the place (+/- 30 deg), and the speed (vector length) varies widely (+/- 50% or more).  It makes it pretty much unusable for figuring out where a boat is going and how fast it's traveling.  Navico says they are committed to fixing the problem, and I'm sure they will since it's such a glaring bug.  But it's been in the systems for a long time.  I know at least two people with Simrad radars that are 2+ years old the exhibit the same behavior.

You will see that the chart below covers Simrad and Furuno.  Notably missing are Garmin and Raymarine.  Why?  Well, because.  Just because a long time back I rejected them for various reasons - reasons that may no longer be valid - and have just never looked back at them.  If anyone wants to contribute the chart entries for those products, please feel free to send me the data and I'll add them in.


Feature Simrad TX10s, and 4G Furuno FAR2xx7 Furuno TZTouch Furuno NN3D Furuno 1835
ARPA/MARPA MARPA ARPA ARPA ARPA ARPA
ARPA targets 10 100 30 30 10
ARPA Vectors R, T (1)(2) R, T (1)(2) T T R, T
ARPA Track History T T none T T
Echo trails R R, T R, T R, T R, T
AIS Vectors R, T (1)(2) R, T (1)(2) T T R, T
AIS Track History none T none T T







Notes





1 AIS and ARPA vector settings are linked.  Changing one changes the other too.
2 Data box changes to report rCrs, rSpd, etc









R=Relative





T = True





What you can see from the chart above is that only Simrad and the Furuno stand-alone radars have support for relative motion vectors.  The more consumer oriented radars from Furuno don't have this important navigation feature, and they even dropped Track History in moving from NN3D to the TZTouch series - clearly a step backwards, in my opinion.  But when asked about it, Furuno said I was the first person to ask about it since the TZ was released.

I think what a lot of this says is that the vast majority of recreational boaters don't know how to really use a radar for navigation and collision avoidance, and until the last 6 months, I'd count myself among them.

I did a little poll on TrawlerForum to see how people use ARPA.  I would consider the audience to be among the more knowledgable in the overall population of radar owners.  32% didn't know what ARPA was or never use it.  And only 24% use it regularly.  The rest use it occasionally.  And even if you are among the minority who use ARPA on a regular basis, if all you have ever experienced is your Simrad ARPA, you would naturally assume that's just how it works.  That was certainly the case among my friends who have Simrad radars.  I only knew something was broken by comparison to my Furuno NN3D on my Grand Banks.  That's what got me digging into this.  But at that point I knew nothing about relative motion vectors, and when/why you would use them.

So I started reading books and trying to figure out whether the radar was messed up, or if I just didn't know what I was doing.  It turns out both were true.  Perhaps ignorance is bliss.  Between reading books, and taking a radar certification course, I now know a whole lot more than I did before.  I'm allegedly now qualified to operate the radar on any ship, of any size, anywhere in the world.  I'm not quite sure I believe that, but it's my story and I'm sticking with it.

Ironically, the Simrad radar is the most feature-complete of the consumer-oriented radars, having the key features that Furuno's NN3D and TZTouch do not have.  Hint, hint, Furuno.  Except for Simrad's extremely broken ARPA, I would likely be happily using my old system today.

I was asked which of the Furuno FAR2xx7 models I plan to use, and whether I'll use it with one of my existing monitors.  I'm planning on either the 2117 which is a 12kw open array, or the 2127 which is a 25kw open array.  In both cases, I'll be using the Black Box version which just means I'll be using my own monitor.  The video output from the radar is 1280x1024, or 1600x1200.  I know 1280x1024 works well on my monitors, though it leaves black bands in the unused space given their 1920x1080 native resolution.  I'll also try running at 1600x1200, but expect the scaling will degrade the image enough to make running at 1280x1024 preferable.  After all, I'd only be losing 27 lines top and bottom by not utilizing the full 1080 height of my screen.  But experimentation will ultimately decide.

3 comments:

Anonymous said...

Hi Peter,

I just read your radar comparison. We have the Furuno NN3D and I can assure you that it displays both relative and true motion for ARPA and AIS targets, as well as provides track history for both.

Mark

Peter Hayden said...

Hi Mark,

Thanks for the comment. I have the NN3D on my Grand Banks as well. I agree with you about AIS track history. That's an error in my chart and I'll correct it. Thanks for pointing it out.

But on relative and true motion, I think we are talking about different things. Read on, and if you still disagree, let me know and I'll keep digging into it.

All radar's that I have encountered have two viewing modes; relative motion and true motion. This is easy to confuse with relative and true motion vectors, and relative and true echo trails.

Since all radar's seem to support relative and true motion views, I didn't include them in my comparison, but let me describe it and we'll see if that's what you are referring to on the NN3D Radar.

The View is what you see on the screen. With a relative motion view, the screen view is always centered on your boat, and the landscape moves through the view as you pass it by. With a true motion view, the screen view is locked on a lat/lon, so land masses don't move, but your boat does move across the screen. This is independent of echo trails, for example, though echo trails will appear very differently in the two views. In a relative motion view, land masses will have echo trails because they are moving on the screen. Another boat running exactly parallel to you will have no echo trail. In true motion view mode, land masses and buoys will not have any trail. Boat's moving will have trails.

Relative and true motion vectors and views are different things, though unfortunately share the same words so can be confusing. The vectors are the lines emanating from ARPA and AIS targets, and only from those targets. Echo returns that have not been acquired as targets will not have vectors. These vectors represent the speed and direction of movement, either true or relative. Let's take an example of another boat running exactly parallel to you. It would have a true motion vector equal to your own course and speed. But its relative motion vector would be zero. A buoy would have a relative motion vector equal, but opposite your own course and speed.

So on the NN3D radars, on the popup menu there is a "True Motion" option that you can select. I believe that changes the view mode (Furuno calls it the Display Mode), but has no effect of the vectors. Let me know if you disagree.

admin said...

Hello Peter,

You have done a good job. Very detailed and informative comparison. If someone asks me this question, I would prefer to use technically more professional Furuno FAR2XX7 unit over other if it suits my pocket. Or may be I would go for a used Furuno marine radar of the same series.

Thanks.

J.