Henning Dürr's "ridiculously broken" Simrad 4G MARPA screens

 

Editor note: I've put Henning's comment from the main Navico MARPA entry on this page so that the screens are easier to see in context with his comments. All words and images below are courtesy of Henning Dürr.

Peter's comment {aka "twistedtree"} makes a lot of sense to me and his experience clearly shows that the problem is not tied to the 4G or Broadband radar but to "Navico" or, at least, NSS and NSO and their supported radars. Before we all get into an endless technical discussion, dear Navico radar owners and prospective buyers, please just have a look at this set of screenshots, taken near the Danish islands of Mon and Sjaelland on this summer's cruise: Target 2 just finished acquiring, as can be seen from the trail just beginning to form. It's a sailing yacht of maybe 40 feet. The vector is slightly off but this may be due to it being just finished acquiring. This was at night with good visibility. I don't like that the yacht only shows up at about 2 miles but that is another topic. Let's stick to Navico MARPA:

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The vector on #2 (the yacht) is still off, even more than before, but not extremely so. I have just finished acquiring target #3, a fast-moving car ferry. The ferry is going down the coast on a course almost due south so the initial vector is way off on this major target:

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The #3 ferry's vector is even more off, not that it would make much of a difference, but notice the length of the vector that has just doubled. There is almost no sea and we are motor-sailing in very little following wind:

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The trail of the #3 ferry is beginning to show, confirming its southerly course. Notice both target's vectors remain off in a smiliar direction, so "consistent". This is a critical point! We are not talking about measurement errors making the vector swing all over the place. The vectors are moderately off or totally off and *consistent*:

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The trail on #3 is well developed and its vector still points north-west. #2's vector is not nearly as far off, almost OK:

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A change: #2 is more off and #3 far less off but still off to the wrong side. I don't recall the vectors ever flipping sides. They are either off to port or to starboard and they stay that way:

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The sailboat is at 1nm distance now. It will be lost soon:

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The sailboat was lost at about 1.5nm. The ferry's vector is still off on its starboard side:

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My own conclusion: this MARPA function is useless and I will continue to call it ridiculously broken.

My learning from Peter's well documented experience: this problem also shows with NSO and with a Simrad 10kw open array.

My learning from our 6000nm sabbatical cruise: of the three uses of radar, inshore navigation and approach, passing situations and weather, passing situations is the most critical for me. I did not have this view before the trip but changed my mind during one hair-raising experience where a cruise ship was bearing down on us at 15 knots (CPA 0.3nm), we were the stand on-vessel and I was absolutely unable to tell if they would pass ahead or astern. I didn't know which way to turn for a last-minute manoeuver or whether to speed up or slow down. I called them and they agreed to change course but then they didn't for 20 minutes.

So I am now a yachtsman saying MARPA (in fact: ARPA) is critical to safe navigation (with the possible addition "in open waters") and no argument will make me change my mind on this. With passing situations, it is all about motion vectors, ideally relative motion vectors (not true) because only these clearly show if a ship will be passing ahead or astern. Interestingly Navico does offer relative motion vectors but, as can be seen from the screenshots, I don't think I would be able to tell the difference.

On the positive side, look at this screenshot:

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You can practically use the radar to find a vacant slip. A while back I heard a Furuno dealer cynically naming 4G a "parking aid".

Back to Marpa on small radars, is Navico 4G especially bad