Radar Range Claims

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mikehar

Senior Member
Joined
Nov 3, 2019
Messages
153
Location
USA
Vessel Name
Gallivant
Vessel Make
Northern Marine 64
I am currently exploring new radars and haven't given much thought to the claims made by Garmin and Furuno regarding their products. I have a straightforward question. If I understand the formula for calculating visual range on a spherical surface (even though the Earth isn’t perfectly round, it's acceptable for our purposes), an observer at a height of 40 feet can see a 40-foot tall object approximately 13 nautical miles away. Beyond that distance, it’s beyond the horizon. How is it possible for radars to claim a range of 72 nautical miles?
 
Electromagnetic radiation is not like a laser, it is a beam with a generally finite width by degree in both the vertical and horizontal planes... horiz. beam width can be as little as less than a degree, vertical beam width much wider on the order of 20 degrees... I have seen aircraft on the order of 35,000 ft up from 240 nm away from the top of a mast. That was a qtr million watt S band unit using a 12 ft parabolic dish and 28 knobs & switches to dial in whatever you wanted... btw, the earth tends to pull signals around itself to some extent, you just have to be curious enough to understand what's happening when it happens.
 
Your radar will pick up an airplane 72 miles away at 5’000 feet. Not much use, I get it.

Even an 18” antenna is going to give you all the performance you need if it’s mounted only 10’ off
The water. Where things get different is trying to burn through rain between 6 and 12 miles out or if you need to distinguish between two canoes or a 16’ hobie cat.
 
I want to ask what is the perceived need for such range on a recreational boat that is also outfitted with GPS and plotter?

Long ago in the time before GPS and plotters I used radar range and bearing for coastal navigation. Longer range than that required for collision avoidance was helpful. But I never had anything like 72 mile range. That was on work boats with the radar antenna 15 to 30 ft off the water.

Now with GPS, plotter and AIS my radar range is seldom set to anything greater than 3 miles. Usually much less.
 
I wish I had spent the extra money for stronger radar when I upgraded a few years ago. Topic of range is misleading. Totally correct that you don't often need to see 72-nms out - rarely need to see 24-nms out. Heck even 12 is a atretch. But a 6-foot open array antenna (72- mile range) will see a helluva lot more at 6-miles than a 36-nm dome will. Small day marks are much easier to pickup for example, as are mooring balls in heavy fog. Images are much crisper so less interpretation is needed.

Range rating is a distraction. But it is an indicator of antenna strength so the metric is useful in a bank-shot sort of way.

Peter
 
I am currently exploring new radars and haven't given much thought to the claims made by Garmin and Furuno regarding their products. I have a straightforward question. If I understand the formula for calculating visual range on a spherical surface (even though the Earth isn’t perfectly round, it's acceptable for our purposes), an observer at a height of 40 feet can see a 40-foot tall object approximately 13 nautical miles away. Beyond that distance, it’s beyond the horizon. How is it possible for radars to claim a range of 72 nautical miles?
with the new gen of broadband radar sets range is much a forgotten spec. those sets are poor at long range but surprisingly excellent at close range where it is most useful. far more useful for small floating objects pulse radar must be perfectly adjusted to have any chance for the typical pleasure boat operators to see... still the BB units can be ranged out to see shipping at sufficient range, no problem. if you currently have a pulse radar keep it and add a BB unit for night or required operation... those are 2nm range or less situations.
 
I don't see any need for a long range radar on a pleasure vessel. At the speeds (5 - 6.5 kts) that I am going a 30 min warning is good enough for me. All the commercial vessels have AIS, so I will get that warning as well. I will see them coming from far away.
The smaller vessels, at least in the area where we are sailing, are either sailing vessels doing about 6 kts as well or superyachts doing around 10 kts, but also those do have AIS.
So at night I set the radar at 6 nm, which will give me more than enough time to take evasive action if needed.

I.o.w. for me the long range capacities are totally irrelevant, I want to be able to see everything that comes within my 6 nm range. As long as the radar does that I am happy. On top of that I have my Sionyx Nightwave, which gives me basically a daytime view and the whole combination makes me feel safe enough.
 
I don't see any need for a long range radar on a pleasure vessel. At the speeds (5 - 6.5 kts) that I am going a 30 min warning is good enough for me. All the commercial vessels have AIS, so I will get that warning as well. I will see them coming from far away.
The smaller vessels, at least in the area where we are sailing, are either sailing vessels doing about 6 kts as well or superyachts doing around 10 kts, but also those do have AIS.
So at night I set the radar at 6 nm, which will give me more than enough time to take evasive action if needed.

I.o.w. for me the long range capacities are totally irrelevant, I want to be able to see everything that comes within my 6 nm range. As long as the radar does that I am happy. On top of that I have my Sionyx Nightwave, which gives me basically a daytime view and the whole combination makes me feel safe enough.
In principle, I agree. However, not all large ships have AIS. It's routine to come across large fishing boats off the coast of Mexico (and other countries, I assume) with no AIS. IMO class ships all have AIS. That said, I don't really need to see anything more than 15nm away. Moving along at 8-9kts gives us plenty of time to get excited about seeing another boat in the middle of nowhere.
 
In principle, I agree. However, not all large ships have AIS. It's routine to come across large fishing boats off the coast of Mexico (and other countries, I assume) with no AIS. IMO class ships all have AIS. That said, I don't really need to see anything more than 15nm away. Moving along at 8-9kts gives us plenty of time to get excited about seeing another boat in the middle of nowhere.
Yes, AIS has a power switch. I've had a CG vessel, a 51 or 87 boat with AIS turned off pull out of Miami as I went by off shore, they matched my speed and speed changes and hung out on my stbd quarter a few miles back almost in the shallows... they matched the 9 knots of the navy patrol craft yacht conversion for an hour and a half and then they turned on AIS and ran up to 12.5kts as our Furuno 4kW ARPA reported. A boomer transiting the Strait of Juan De Fuca never had its AIS on...
 
I wish I had spent the extra money for stronger radar when I upgraded a few years ago. Topic of range is misleading. Totally correct that you don't often need to see 72-nms out - rarely need to see 24-nms out. Heck even 12 is a atretch. But a 6-foot open array antenna (72- mile range) will see a helluva lot more at 6-miles than a 36-nm dome will. Small day marks are much easier to pickup for example, as are mooring balls in heavy fog. Images are much crisper so less interpretation is needed.

Range rating is a distraction. But it is an indicator of antenna strength so the metric is useful in a bank-shot sort of way.

Peter
Discrimination has everything to do with array width, and very little to do with power or range. The array size (width) determines the focus of the beam. I'd be a lot more interested in something with better discrimination at 3 miles, than any capability at all at 12.
 
I had a 6KW 6' open array Garmin on my 45' Cherubini. With decades of experience on lesser radars, you don't know what you're missing until you get a better unit.

First, many multi function displays have dual screen capability, giving you the ability to see the crab pots on flat water on 1/8th mile range while simultaneously seeing the freighters at 10 mile range in the Chesapeake.

The 6' open array allows you to determine there's a 25' center console fishing next to the seabouy, as opposed to the 18" closed array that shows one target.

Lot to be said for seeing the frontal boundary storm at 72 miles instead of 24 miles.

This assumes you travel at night or unforecast fog has reduced visibility to a 1/4 mile. When you're piloting by instrument, isn't the time to learn your radar or wished you'd have spent more on a better one.

Ted
 
Your radar will pick up an airplane 72 miles away at 5’000 feet. Not much use, I get it.

Even an 18” antenna is going to give you all the performance you need if it’s mounted only 10’ off
The water. Where things get different is trying to burn through rain between 6 and 12 miles out or if you need to distinguish between two canoes or a 16’ hobie cat.
power gives you the ability to resolve smaller objects floating in the water close aboard and small but still large enough to poke a hole in your boat or kill the person in the kayak. only focusing on ships that you're afraid of is not a proper radar watch.
 
Discrimination has everything to do with array width, and very little to do with power or range. The array size (width) determines the focus of the beam. I'd be a lot more interested in something with better discrimination at 3 miles, than any capability at all at 12.

"Discrimination" is the right world. The new digital units promised enhanced and affordable discrimination at short distances but in my opinion, fall short. They are better than their magnetron predecessors of similar size, but not all that great. Ted/OC Diver also makes a great observation - until you've spent some quality time with a higher power system, you don't know what you're missing. Literally.

The use case for radar on most recreational boats is pretty limited. Vast majority of boaters can and do avoid circumstances where radar is really helpful. They have radar for those rare situations where it's needed. Unfortunately that's exactly when you want/need the best discrimination possible.

I don't see any need for a long range radar on a pleasure vessel. ....., I want to be able to see everything that comes within my 6 nm range.....
I agree with you - no need for long range radar, especially at trawler speeds. But that's the trap - the underlying assumption is that at shorter, useful distances, both units perform similarly. They don't. Not even close. If you want crisp definition at 3-6 miles, a long range radar will outperform a short range one by a long shot. You're not buying distance, you're buying clarity.

Peter
 
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Any radar is better than no radar, but the more powerful ones are even better.
 
Question related to close range targets (logs, crab pots, etc). I have two older Furuno radars-open array and dome. I will not get rid of the open array. Are the new broadband radars worth it in regards to picking up close range targets? Will my open array pick up these close range targets as good as a BB?
 
Question related to close range targets (logs, crab pots, etc). I have two older Furuno radars-open array and dome. I will not get rid of the open array. Are the new broadband radars worth it in regards to picking up close range targets? Will my open array pick up these close range targets as good as a BB?
What's your definition of older? Mine is where you stick your face in a rubber cone coming off the radar and you're looking at a vacuum tube. The radar on my boat is now 10 years old and does a fantastic job. The open array is 13' above the water. It could still see crab pots at 100 to 150' off the bow and see 6' tall buoys at maybe 75' to the side.

Ted
 
You got me beat. You’re also good for an EMP strike! Im not on the boat right now, but it’s a 4 foot open array, probably 20 years old. Im wondering about replacing the Furuno dome-probably the same age-color display. Dome works fine for larger objects, but nowhere near the clarity or detail of the open array. Incidentally my brother has a great story of a new crew member steering a gill netter, headed to Alaska at night, solely with his face buried in the rubber cone! Hey, captain said to use the radar!
 
To the OP: I have asked the same question years ago when I got into boating. The answer I got from people like TT is. The radar needs to though fog and rain. In short, the more power (distance) the better.

I will say, you want the narrowest horizontal beam you can get. This will give you target separation. As in, two buoys may look like one.
 
Used to be, one reason for long range radar was about weather. These days, except for a fair distance off-shore, weather radar returns are relatively easy to come by. Sirius weather, websites over the 'net, local TV news, etc.

Otherwise, range by itself doesn't do much to ring my chimes. I'm more interested in clarity, discrimination, and returns from nearby small objects (crab pot floats) than I would be in distance.

-Chris
 
If I am caught in bad weather. The news is not going to tell me if a fast boat is is coming at me 5 miles away. But thats me........

Here in N.E. we have lobster traps. My Gamin 24" dome 15yrs ago would not pick them up unless I turned the gain up. But then the screen was showing waves as targets. My newer Simrad Halo+ does pick them up with turning the gain up without any false targets. I have to be mindful of this. At times I think there is a boat broadside of me 2 miles out and its a trap I cant see. So I only turn the gain up when needed.
 
If I am caught in bad weather. The news is not going to tell me if a fast boat is is coming at me 5 miles away. But thats me........

Sure... but generally a "72 mile" radar isn't required for a boat 5 miles away. And in our typical navigation, a fast boat 5 miles away is a non-issue anyway... at least for a while... because of that whole "5 miles" thing. We're usually much more concerned about boats within a mile or so.

Or crab pot floats dead ahead at 30 feet. And all around us, and all around any conceivable path we might think of trying to get through the field...

-Chris
 
You got me beat. You’re also good for an EMP strike! Im not on the boat right now, but it’s a 4 foot open array, probably 20 years old. Im wondering about replacing the Furuno dome-probably the same age-color display. Dome works fine for larger objects, but nowhere near the clarity or detail of the open array. Incidentally my brother has a great story of a new crew member steering a gill netter, headed to Alaska at night, solely with his face buried in the rubber cone! Hey, captain said to use the radar!
I had a Furuno Navnet I display with 4' open array circa 2002 on my charter boat. I would say it was good, although my buddy's 6' array 10 KW was a night and day difference. As important is the size of the display. When radar was the highest priority while underway on my trawler, I would switch the chart plotter to the 8" display and put the radar with the split screen, on the 15" display. Happiness is networked MFDs!

On the charter boat, I added a second Navnet with about a 30" dome radar and the two displays networked through a router (back in the old days). I was running enough night trips that I needed a backup radar. While I could use the dome if the open array failed, it was disappointing in comparison and hard to force myself to practice with it on nice days.

Ted
 
I agree with you - no need for long range radar, especially at trawler speeds. But that's the trap - the underlying assumption is that at shorter, useful distances, both units perform similarly. They don't. Not even close. If you want crisp definition at 3-6 miles, a long range radar will outperform a short range one by a long shot. You're not buying distance, you're buying clarity.

Peter
I don't say that at shorter range my radar will perform better. All I am saying is that, where I am sailing, the radar is able to pick up all the important targets that I need to be aware off. At night there is not a lot of traffic on the routes we are doing. If there is traffic, e.g. near Athens, then 99 % is commercial and they do have AIS. I can overlay my AIS targets with my radar targets so I know who is who.
Anything without AIS will show up on my quantum radar and it will show me speed, bearing, range and direction of movement. Based on that I can point my Sionyx in the direction of the target and I have all the info I need.

Would I have a different set up in a very busy environment ? Probably.
Would I have a different set up if I needed to do a radar approach into a port ? Perhaps, but even with what I have now I do night time approaches into narrow, unknown, ports, anchorages and marinas.

I.o.w. you can always get better equipment, but for what most of us need it is not necessary to go ballistic on equipment. If you want to do it, can afford it and it makes you feel safer, then by all means go ahead. I am very comfortable with the current set up and won't be changing it anymore in my lifetime (unless it breaks down).
 
For recreational purposes, I think a 72 mile radar capability, is like my car being able to run 130mph. What will I do with it that’s useful?
 
For recreational purposes, I think a 72 mile radar capability, is like my car being able to run 130mph. What will I do with it that’s useful?

My car goes 185 mph. True, I will never go more than 1/2 that but what enables the vehicle to go that fast also enables it to tow 8,000# and to accelerate rapidly enough to merge safely. You might not need 72 miles but you might need to burn through the rain or to distinguish between two boats close to each other or one large boat.
 
The issue is the range spec yardstick for comparing radar is incredibly misleading. When taken in isolation, there is very little reason for a radar range more than 12-miles or so, at least for trawler/sail speed boats.

There's an old saying that you cannot tell a tadpole what it's like to be a frog. Similarly, for folks who have never used a higher power radar, it's hard to describe how much more useful they are at 12-miles (example). Whether you need the enhanced definition, clarity, and precision is a different subject. But make no mistake, at 12-miles (or even 3-6 miles), a 72-mile/6kw radar array provides significantly more visibility than a lessor counterpart (say, 36-mile) even though both are operating well within their specified ranges.

Range as a selection spec needs context. It's an indicator of power - the distance should be discarded.

Peter
 
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