The following comments were first posted on a Panbo entry about the Vestas Volvo race boat wreck and grounding alarms but whereas we got pretty far off track I've moved all but the first one to here. Hopefully this will also mean that folks searching for 4G performance information will find this forum post, and I'm really hoping that sailors who've used 4G a lot offshore will report in.
I have doubts that any radar and particularly 4G mounted low on the boat, like on a post or arch at the stern, about 12ft from the water, would have clearly painted a reef and surf line. My experience with such a radar setup in open ocean waters even in fairly nice conditions was disappointing. I put this down to:
- the motion of the boat
- the antenna at 12ft height vanishing completely in the troughs of some of the larger seas
- my Scanstrut self leveling mount overswinging significantly. It should have much stronger damping IMO. I would no longer dare to put a unit like this up on the mast where the motion is much stronger again.
I think it is these three effects that work together to make real targets vanish and pop up again and make them jump around and this is then compounded by lots of false echoes from sea returns. The target filtering of the radar display and my own "filtering" when looking at the screen then blend out (discount) the real targets, even a container ship at 6nm.
When motoring in calm seas that same radar clearly showed the volcanic island of La Palma at 28nm range but then there was no real risk of us hitting that island. When there was a real risk, on passage from the Azores to England, I had to rely on AIS, especially at night when eyeball visibility was low in fog or drizzle. This is in spite of me spending many hours playing with the settings.
The radar alarm was unusable because of constant nuisance triggering or else, with the sensitivity down enough to avoid nuisance triggering, the radar would be basically blind.
In situations like what Vestas Wind had when approaching the reef, I think one would need the antenna way up at the mast and maybe a powerful magnetron.
Posted by: Henning at December 13, 2014 5:42 PM | Reply
Am I correct to say. The 3G/4G radar is great radar for inland cruising and low speed sailing but when you are sailing offshore or motor boating on high speed you do need a serious old school high current radar.this because of the range issue ?
Posted by: tcy at December 15, 2014 2:47 AM | Reply
I don't think that's correct, tcy, and certainly not definite. As I've written before I think there's something wrong with Henning's 4G radar, as the performance doesn't seem related to what I'm seeing with about the same antenna height.
Posted by: Ben in reply to tcy at December 15, 2014 8:01 AM | Reply
What should be wrong with my radar? La Palma showed perfectly at more than 28nm and in the large marina where we are now in Hamburg, I have spectacular performance and can tell which one of the 200+ slips is empty and which is filled. You shouldn't but probably could safely dock the boat from below at the nav station.
I chose this radar for its close range performance and for that you need to mount it low or else the 25 degree horizontal opening angle of the beam (12.5 up and 12.5 down) will look clear over everything you would want to see. I sometimes see BR radars mounted above the first spreader and wonder why the owners chose this combination of radar and position. But while the low position helps close range, I feel that it is a serious impediment in large swell because of all the false echoes that hide the real targets.
I can't say that you would need a "serious" magnetron radar for long range because I haven't tried it. The only comparative test of current production leisure boat radars I know of is Ben's and he says it compared OK to magnetron radars. But I did hear from other Atlantic sailors that I probably wouldn't be able to use the radar alarm with a low mounting position which turned out true.
Maybe Ben would care to take Gizmo out into the Gulf Stream in a northerly winter gale. 16 foot seas, tide against current and all, and let us know the results ;-)
However, if someone asked me for a recommendation for an ocean crossing watchkeeping and weather radar, I don't think I would recommend the 4G.
And yes, if you do these passages, you do want a radar.
Posted by: Henning at December 15, 2014 4:33 PM | Reply
I don't know what's wrong with your 4G, Henning, but here's what you wrote on another thread ( http://goo.gl/0doFx ): "...when crossing from the Azores to England, I could reliably see large container ships at only 2 to 4nm while I could see the same ships on AIS at up to 90nm." That's terrible radar performance almost regardless of sea conditions, and not what I've seen from 4G. It's true that I haven't had Gizmo out in truly big seas, and don't plan to, but I can report that in 3-4 footers with whitecaps, the 4G seems to handle sea clutter about as well as the 3 other test radars, all of which are 4-5 feet higher.
Posted by: Ben in reply to Henning at December 15, 2014 4:54 PM | Reply
Henning has doubts that any radar would have clearly painted a reef and surf line. I have doubts too, but for a different reason. Everybody regards returns from waves as noise, so they are deliberately suppressed as much as possible. We know that radar can see waves and boat wakes, although it does depend on the wave shape.
With shipping using AIS, what exactly are you watching for on radar on a passage? Radar is not currently smart enough -- blips come and go, where is the feature that determines which are real and tracks them, a more advanced MARPA which doesn't just drop a target if it misses a few scans. A radar where you can change the range and the blips on the screen (which are real targets) do not disappear into a dust speck sized pixel or two.
Posted by: norse in reply to Henning at December 16, 2014 3:02 AM | Reply
Norse: I think the reasons for your and my doubts are the same. Maybe I wasn't clear about "reliably see a container ship". I don't mean that the ship gives no return but that all the wavecrests around me give returns, too, and all these false return obscure the container ship until it's as close as about 4nm. Before that, the ship's return keeps vanishing when I (not the ship) am in a wave trough and so looks and behaves just like all the other false returns. I tried everything with gain and the other settings but there was no setting that would suppress the sea echoes while not suppressing the container ship.
Remember we are in the open ocean here. When we left the English channel near the beginning of our trip I was in awe for hours about the size of the rollers that had come from some distant place like Newfoundland and were traveling at a stately speed for thousands of miles. For the most part, they were completely benign. It's like a rolling hillside. You feel an urge to ski down them (which I did sometimes in our planing dinghy). Sometimes we motored in dead calm and when I closed my eyes I could feel being lifted and set down like in an elevator for one or two stories. The west side of La Palma, in place called Tazacorte, is where they make contact with land. They have a monumental breakwater there, 15 metres high, with 10s of thousands of tons of concrete. The first one they built turned out too small and the second one had cost EUR 53 million in EU grant money. This is to protect a couple of pleasure- and tour boats worth maybe 2 million in total...
I guess even a 48kw magnetron radar will show zip useable returns if hidden completely in a wave trough.
I conclude that for these applications the radar must be up in the mast (and it probably wouldn't hurt if it were really powerful). This should significantly reduce the amount of false echoes from seas and at the same time give consistent returns for real targets so they stand out better.
This is the complete opposite of my experience years earlier in the Kiel Canal when my old 2kw magnetron radar that came with the boat and was mounted above the first spreader failed to show the banks of the canal because it was looking over it and instead showed me farmhouses and outhouses a good distance from the canal. My conclusion then was that I really needed a radar with good close range performance and it needed to be mounted low.
It seems that I need two radars... Only I fear that people will laugh their butts off when they see my boat. RODL - rolling on the dock laughing.
Ben, do you have some relevant experience with this?
Posted by: Henning at December 16, 2014 4:11 AM | Reply
I think Henning confirms my thought. 4G radar is great inland but out of the green into blue you do need some power. it's great to see the harber overlay and the mooring poles but on the ocean or north sea you also would like to see further ahead.
Posted by: tcy at December 16, 2014 5:36 PM | Reply
There are many bluewater boats using 4G. What Henning is describing now are pretty extreme conditions that will probably affect the performance of any radar not mounted way high. I've sailed from the Canaries to the Caribbean and many times from there to New England, but I've only seen swells like "rolling hillsides" once. I didn't have a radar at the time but wouldn't be surprised if one at 12 feet had trouble.
What I don't understand is why his 4G wasn't performing better when his boat was at the top of those hills. I've run 4G side by side with the best competing radomes for several years and don't think there's a big difference at 4 miles.
Posted by: Ben at December 16, 2014 6:18 PM | Reply
tcy: Your thoughts are yours of course but what I said was that I conclude from my not exactly extensive open ocean experience that you would want your "watchkeeping" radar mounted high to:
1. reduce the amount of false returns from seas ("sea clutter")
2. make real targets paint more consistently, at every or nearly every sweep
There are two different types of seas, wind sea and swell. NOAA wave models (at least the one ZyGrib uses) even have independent data for both (separate values for period, direction and height).
The wind sea is what bounces your boat around, gives you seasickness, causes a big pot of spaghetti to come off the hob even with the potholders in place (a huge mess in the bilge) and causes the toilet lid to slam shut before you have a chance to turn around and sit down (I need a bungee cord here). It also puts a strain on the self leveling radar mount so that it probably hurts more than it helps.
Swell is completely benign and gives you no more discomfort than an elevator. There is hardly any rolling of the boat associated with it. You can leave a glass of water on the cockpit table in 4m/12ft swell. It's safe to dinghy about in it. You can hear the outboard strain when you're going uphill and rev up when you slide down a slope.
Swell and wind sea are often overlaid. Then you can no longer feel or see the swell but it's still there, lifting you up and down and blinding your low mounted radar in the troughs.
I have never seen and will do everything I can to avoid ever seeing a 4 or 5m wind sea. On our 6000nm sabbatical we were able to completely avoid this which makes me believe or hope that it can be avoided pretty reliably.
But you can't really avoid the swell (and why would you?). You would need a completely depression-free North Atlantic for that for at least 4 consecutive days which is never going to happen.
There is almost always some nasty depression out there somewhere where you don't want to be and aren't going to be. This kicks up a big wind sea and the rollers then emanate from the center of the depression or the area of strongest winds as the ripples do when you throw a stone in glassy water. Larger waves travel faster (I read that the tsunami wave hitting Asia traveled at jet airliner speed). An they go great distances without losing their strength. So a day or two later they reach the warm and sunny and mostly wind-free area where you are.
When we moved down the Portugese coast in Fall 2013 we had plenty of opportunity to see swell by itself as there was a series of depressions taking a southerly route and giving us strong headwinds. So we had to wait out the storms repeatedly and then motor south in the windless windows between them. In all, we motored or motorsailed 80% of the distance from Hamburg to Rabat, Morocco. And in the Atlantic we always had significant swell, coming from wherever.
There are rarely stormy winds in Portugal but only 3 harbors on it's Atlantic coast are safe to enter in any conditions. All others have a bar over which the swell breaks. In early 2013 a German 44ft sailboat was totalled in the entrance of Figuero da Foz causing 2 deaths and this was in near dead calm. For all I know, the swell that did this may have come from a depression near the Falkland Islands.
So, getting back to the topic and answering Ben's question, my radar did paint the real target very well when on the top of the wave but then it was lost again a moment later when in the trough. So it's inconsistent and in that it's just like all the other false echoes from seas.
If the real targets would paint at every sweep, they could be seen even if embedded in all the false echoes from seas.
If there were no false echoes from seas, even an inconsistent real target would be seen.
As it is, the real targets look just like all the false targets until as close as 4nm with my radar mounted low in the conditions that we had, which were, I repeat, not severe but as nice as can reasonably be expected in this area (mostly 18 to slightly more than 25 knots true from the aft quarter, making for apparent pretty much on the beam with wind sea no more than 3m, 9-10ft, but with unknown ocean swell underneath).
And yes, there are many blue water boats with BR/3G/4G. And I'm not thinking of replacing it, partly because we aren't planning any Atlantic sailing for a couple of years.
Posted by: Henning at December 17, 2014 4:17 AM | Reply