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Old 26-08-2015, 11:44   #16
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Re: Radar Height and Range

The B&G 4G Radar if the marketing can be believed is sort of like the change from an incandescent light bulbs, to LED's.
I'm talking about the no warm up, no main bang, continuous wave, and lower RF emissions than a cell phone? The whole operating principle if I understand it is different than any Commercially available marine Radar that I have heard of, but lower than a cell phone emissions is hard to believe
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Old 26-08-2015, 11:52   #17
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Re: Radar Height and Range

No one has mentioned the fact that vessels tend to roll. The higher above deck level the antenna is mounted, the greater the arc of swing. I don't think small boat radars lock onto an aquired target because they are seeing and not seeing in a seaway (pun not intended ).I believe that's what's meant by as far or high as practical. The less arc the more a target will appear through successive sweeps.
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Old 26-08-2015, 11:52   #18
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Re: Radar Height and Range

Quote:
Originally Posted by Paul L View Post
The need for distance is overrated for Radars on a cruising boat. Resolution is far more important. A 24"dome will have much better angular resolution that a 19" - no matter what the power and distance spec'd by the seller is. We are most interested in good resolution and closer in operation for traffic avoidance and navigation. We use long distance ranges to look for storm cells. In this case it doesn't matter what your radar height is as the storm height is way up there. We also use long distance ranges to verify that our charts match up with reality, again dome height is not important in this case. The lower dome height might have some issues with big seas, getting blocked at the bottom. In this case the dome mounted at 45 feet off the water is going to be swinging wildly about as the mast gets bounced around, so the radar single is not going to be that good anyway.
You can play with dome height and target heights here to get max distances:
Radar Horizon Calculator
Example that might apply to a freighter in the distance
Radar height 15ft, target height 60 ft = range 14miles
Radar height 35ft, target height 60 ft = range 17miles

All of this corresponds well to my practical experience.

I have a 4G radar mounted 10 meters above the waterline (about 33 feet).

Radar performance is much degraded in rough weather, apparently from the motion of the dome up the mast and from high seas. Also is much degraded if the boat is heeled over much over 15 degrees or so.

I don't really care about radar targets much over 10 miles out, unless they are storms, in which case the antenna height doesn't matter. Or land features -- ditto. Large ships have superstructures very high above the sea so you can see these from further out in any case.

So I doubt if the extra height means much in my particular case. Maybe the air is "cleaner" up there and there is less sea clutter -- about the only real advantage that I can think of.

One really huge advantage of 4G radar is that it has remarkably few false targets -- the resolution is high enough and signal processing effective enough to eliminate clutter and false targets with great efficiency. To such an extent that the guard zones are extremely reliable and useful. This is really great and justifies the choice of this system all by itself in my opinion.

On the other hand, the MARPA implementation on the 4G radar is very poor -- cannot keep a good lock on small targets, and does not perform all that well even with large targets (which are anyway emitting AIS). I hear tell that Furuno radars do a much better job with this, but can't confirm with my own experience.
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Old 26-08-2015, 11:52   #19
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Re: Radar Height and Range

If you are driving a 300mph hydroplane going from 15mile to 50mile range is useful as you go from a 3minute range to a 8minute range.

If you are driving a 5mph cruising boat, 15miles is still 3hrs away. Even if it's a ship closing at 20mph, you still have upwards of 45minutes to see it.

I would be more interested in close range resolution and just keep it high enough so it's not directly zapping your brain.
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Old 26-08-2015, 11:59   #20
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Re: Radar Height and Range

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Originally Posted by jreiter190 View Post
No one has mentioned the fact that vessels tend to roll. The higher above deck level the antenna is mounted, the greater the arc of swing. I don't think small boat radars lock onto an aquired target because they are seeing and not seeing in a seaway (pun not intended ).I believe that's what's meant by as far or high as practical. The less arc the more a target will appear through successive sweeps.
A valid point. I just looked into a broad band google sight. Maybe everything I thought I knew is wrong with radar, is old school.
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Old 26-08-2015, 12:00   #21
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Re: Radar Height and Range

Quote:
Originally Posted by a64pilot View Post
The B&G 4G Radar if the marketing can be believed is sort of like the change from an incandescent light bulbs, to LED's.
I'm talking about the no warm up, no main bang, continuous wave, and lower RF emissions than a cell phone? The whole operating principle if I understand it is different than any Commercially available marine Radar that I have heard of, but lower than a cell phone emissions is hard to believe
The marketing is highly exaggerated. The principles are indeed different, but the performance is not radically different, from good pulse radar.

The difference is that CW radar emits a continuous signal instead of a pulse. It doesn't need to be silent to listen for the echo, because the frequency is always changing. It can determine the moment of emission of the reflected signal by the frequency. Clever, eh? There's nothing new about it -- been used in fighter jets since the '50's (IIRC).

The continuous signal is much less powerful so in theory doesn't punch through rain as well and doesn't have as much range. But is capable of higher resolution with a smaller dome. In my experience, both the range and resolution is similar to good pulse radar. I do like the fact that the dome is smaller and lighter, and power consumption somewhat (not radically) less. It seems to work better at extremely close ranges (I can see my own anchor), but this has no real useful application. In my opinion, there is nothing really radically different from Raymarine or Furuno pulse radar, and the MARPA implementation may be worse. Other than MARPA I'm perfectly happy with mine, but if I were buying (or building) a new boat, I might consider Ray or Furuno instead, if I preferred the other parts of those systems.
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Old 26-08-2015, 12:16   #22
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Re: Radar Height and Range

If you buy whatever a60 ton fishing boat is sporting,that's a good enough unit to get the job done on any yacht. That's how Furuno got into the yacht market; they offered something reliable at an attractive price. With small boats it's a luxury, with commercial vessels, it's a necessity.
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Old 26-08-2015, 12:37   #23
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Re: Radar Height and Range

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Old 26-08-2015, 12:40   #24
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Re: Radar Height and Range

I understand continuous wave in that as the frequency is changing at a known rate, the frequency of the return can be used to determine range based on the time since that frequency was transmitted.
But this ignores Doppler effect? If a target is moving towards you, the return signal will have a higher frequency based on Doppler shift, so how do they get around this? I think they ignore it assuming marine targets will be of relatively low velocity.

I know a little about Radar as I did a little flight testing of the Longbow Radar on the D model Apache and got to have conversations with the Engineers who were developing the thing.
Continuous wave Radar has been around for a very long time, my knowledge of it is old Anti-Aircraft missile Radars, it could be defeated by slowing below it's Doppler notch as it could only "see" moving targets, But frequency modulated continuous wave used for target detection in low cost Radars is as far as I know pretty new.

Now from an operational standpoint, I'm not all that impressed, I don't see it working any better than my Garmin (HD) Radar did, it's different, but I don't have enough time with it yet to make a good comparison, the Garmin I got to where I could tweak it well, never to the point of it detecting birds outside of visual range as some claim though.
The B&G, I haven't played with it as much as I did the Garmin yet.


I think mine is mounted at about 4 m high, I don't get the degradation in rough weather you do, but my guard zones are pretty much useless based on false returns from sea state setting off the alarm. I think the difference is mounting height, I don't get nearly as much swing of course, but having a much lower look down angle to the waves, I think I'm influenced much more by sea state
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Old 26-08-2015, 12:50   #25
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Re: Radar Height and Range

Quote:
Originally Posted by jreiter190 View Post
If you buy whatever a60 ton fishing boat is sporting,that's a good enough unit to get the job done on any yacht. That's how Furuno got into the yacht market; they offered something reliable at an attractive price. With small boats it's a luxury, with commercial vessels, it's a necessity.
Most commercial fishermen have two along with every other piece of electronics. Maybe something to be learned if your fishing the North Atlantic or Pacific? I can't speak to you blokes from down under. I feel sure it is the same. I've only had a pulse Furuno 16mi gave good service but my interest probably didn't involve 7 mi. or less. I don't care what is over the horizon. The container ship can probably see my Clorox bottle if I have a good reflector with their 72mi unit mounter 100+ Foot up. JMO I think radar is over rated.
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Old 26-08-2015, 13:21   #26
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Re: Radar Height and Range

You're dead right about radar being a necessity aboard commercial vessel. I still remember when the skipper finally sprung for one aboard the tow boat we were operating in the PNW. Cost around $20K and that was used off a naval vessel!
It was a godsend traveling in fog and through separation zones of which there were many back in the day. On the commercial fish boats I worked, radar was pretty standard as Cadence points out back in the 70's and later.
The advent of 4G and broadband application for pleasure craft radar has really improved the ability of the casual sailor to travel safely and without the worries they used to have about weather, fog and traffic. Radars today are cheap, easy to use and give a much stronger return than the older type. Phil
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Old 26-08-2015, 15:05   #27
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Re: Radar Height and Range

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You're dead right about radar being a necessity aboard commercial vessel. I still remember when the skipper finally sprung for one aboard the tow boat we were operating in the PNW. Cost around $20K and that was used off a naval vessel!
It was a godsend traveling in fog and through separation zones of which there were many back in the day. On the commercial fish boats I worked, radar was pretty standard as Cadence points out back in the 70's and later.
The advent of 4G and broadband application for pleasure craft radar has really improved the ability of the casual sailor to travel safely and without the worries they used to have about weather, fog and traffic. Radars today are cheap, easy to use and give a much stronger return than the older type. Phil
Phil,
You have that right, dirt cheap so why not have one. In day light and clear weather why eat up the battery. In fog or unformiliar waters looking for a buoy at night a good tool.

I don't think I understand all of the new electronic. I just hope those that do, get home safely if they take a ****.
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Old 26-08-2015, 15:42   #28
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Re: Radar Height and Range

The range issue is really not that important, although higher power and resolution are. The long range stuff was useful for navigating back with celestial and spotty LORAN coverage but today we know where we are. The main use for radar is collision avoidance, whether in fog, rain, or darkness. By putting a dome at, say, 30' height the short range performance is seriously compromised. Coming into a crowded anchorage on a dark night you really need to see nearby moorings and small boats that are under the beam for a high-mounted antenna. For that application the best mount is on a pole, at about 15', and not up high on the mast. In any event, out on the ocean the lower power radars aren't that good at picking up ships beyond 6-8 miles in typical seas (6-8').

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Old 26-08-2015, 20:50   #29
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Re: Radar Height and Range

I have a 24 NM range 2003 Raymarine Pathfinder radar mounted on my mast. I would guess it is about 35 feet up. I can see within a boat length objects next to the boat. Offshore, I keep it on 12 mile range which is plenty for seeing targets at a distance that gives plenty of time to avoid. I do put it out there to look at storms and I have used Marpha to track cells and get an ETA to me.

My only problem with mast mount is when I went up and down the Tenn-Tom and had to lower the mast, I mounted my radar on the front of my boat on my mast cradle so I could travel the rivers during fog and at night. It was a bit of a hassle to take off and remount the radar. I am not sure what I will do when I have to replace my radar with a newer set of electronics. I have been debating this same issue. If I never had to take my mast up and down, I would definitely put it on the mast. I have never had problems with the radar not seeing targets due to heel or rolling motion. I think either approach is ok and it depends more on where you sail and what you are trying to avoid with the radar.


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Old 26-08-2015, 23:38   #30
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Re: Radar Height and Range

Quote:
Originally Posted by jreiter190 View Post
No one has mentioned the fact that vessels tend to roll. The higher above deck level the antenna is mounted, the greater the arc of swing. I don't think small boat radars lock onto an aquired target because they are seeing and not seeing in a seaway (pun not intended ).I believe that's what's meant by as far or high as practical. The less arc the more a target will appear through successive sweeps.
For any reasonably sized sailboat, the height of installation will not affect radar performance. For a fixed installation the dome will roll thru the same angle at the top of the mast as on deck. The accelerations involved may affect the bearings and motor over time which would affect performance.

The key issue here is what is the vertical spread of the beam and is the boat rolling further than that. IIRC most beams are +/- 15* or 25* vertical.

There are self-leveling platforms that can compensate for roll or heel.
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