Pondering Broadband Radar

[Ian_Rob]

When the relative merits of broadband (FWMC) radar and pulse radar are debated, the comparatively poorer range of FWMC radar is raised as an issue.

Users of 3G radar suggest a range capability of around 15nm and a little more for 4G (17-+nm).

Putting that it in perspective, if I an in Hurst Narrows I should be able make out boats in Studland Bay. Do I realistically need more?

For a sailing yacht making 7-8 knots, doesn't 15 -17nm suffice? I don't think I would respond at that distance if I was just relying on my eyes (and probably not at half that distance).

Whilst I am sure it is reassuring to see 'land' on the screen that you can't otherwise see when navigating off-shore, since the chart-plotter will indicate the position of the land, how much does the fact that it is outside radar range really matter?

 

[Neeves]

I agree with your analysis.

Broadband is ideal for a yacht as, at the speeds most of us make, even a 10nm range is adequate. But commercial vessels show up much further, with broadband, and they are the targets that cause us most concern. Couple the short range accuracy (your bow), the long range (10-15nm) capability, low power consumption (especially in stand-by) and instant 'on' and it actually seems a no brainer. I actually wish they had kept the original system, and sold it as a budget model, as it had even lower power usage.

Historically one could use radar as a 'chart plotter' as the coast line showed up so well. But with integrated systems now if you lose the chart plotter you might lose radar as well (depends what the failure is - but most of us have only one screen).

Sadly if you go for 3G or 4G you are committed to a Simrad or B&G system - which might not suit your requirement for your autopilot or chart plotter. Though I lust to change my NSS for the Zeus - simply because of the sailing software.

Jonathan

 

[grumpy_o_g]

I don't think the range is a limiting factor in reality but it's been said a few times that the 3G is not as good as good as some of the other pulsed radars at picking out storm cells - I have no idea how true that is. The short range definition is outstanding on the 3G and the range you can go down to is ridiculously low. Any better and you could use the thing as a parking sensor (which are also FMCW thinking about it). Having said that the latest Raymarine and Garmin are pretty impressive. Have a look at Panbo.com to see their reviews.

 

[jerrytug]

FM radar doesn't show racons or RTEs. Apart from that, the advantages for yachts seem to be overwhelming.

 

[Slipperman]

I looked into fitting a radar in the summer. I got quotes for 3 different radars (one broadband, two conventional) from one of the main dealers in the Solent area. I was attracted to the broadband model but the dealer said that whilst they were fabulous for navigation, showing small targets, even withies, very well, they were much poorer than the conventional sets in rain and heavy fog. Since I would be fitting radar primarily for its ability to see through fog/poor visibility, it made me think. Currently I am still thinking! (And price wasn't an issue - including fitting the prices for all 3 models came out very close). If anyone can provide further info/experience, I shall be grateful.

 

[Ian_Rob]

The short (in reality not that short) range capability of FMCW combined with the low power consumption (18w /2w standby) and the apparent ability to pick out small markers, is very attractive. I am interested in Slipperman's dealers suggestion that the performance is degraded by rain and heavy fog - perhaps Neeves can comment? (Is it ever foggy in Sydney?) Defeats the object if true.

From the manufacturer's website, pulsed radar seems to have a 4+nm advantage in picking up storm cells.

I don't suppose there are any dealers who have boats with both systems on board who can give on the water, comparative demonstrations?

 

[Neeves]

Sorry we do not have fog that often and you would need to be sharp to catch it - before it boils away.

We had a Pathfinder system previously and it was fabulous at picking up storm cells, we could pick them up at 20nm - but storm cells are sufficiently unpredictable in their movements that using radar as 'storm cell avoidance' was luck. Once the cells got close enough we could navigate between 2 cells (and this was not possible visually) as you could see the gap on radar (or see 2 centres and aim to pass between them). Pathfinder was useless in heavy rain it was just a black mass on the screen (black and white screen)

Broadband is the same, but different. It does not pick cells up quite so quickly, 16nm, but picks them up sufficiently close - but they are no more predictable. Broadband seems better than Pathfinder (but the latter is pretty old technology) in rain - it seems difficult to believe it (BB) would not be better in fog.

We get storm cells fairly frequently here, they march across the countryside in line abreast, and if you are 10nm offshore and they develop and come your way there is not much you can do but watch and wait. Its not until they are maybe 2nm away you can make a decision and Broadband is fine. You can see the centres, or you can see the areas the cells cover and aim to pass between them.

Jonathan

 

[grumpy_o_g]

I looked into fitting a radar in the summer. I got quotes for 3 different radars (one broadband, two conventional) from one of the main dealers in the Solent area. I was attracted to the broadband model but the dealer said that whilst they were fabulous for navigation, showing small targets, even withies, very well, they were much poorer than the conventional sets in rain and heavy fog. Since I would be fitting radar primarily for its ability to see through fog/poor visibility, it made me think. Currently I am still thinking! (And price wasn't an issue - including fitting the prices for all 3 models came out very close). If anyone can provide further info/experience, I shall be grateful.

Speaking for FMCW generally rather than the Navico ones - FMCW is actually better regarded in rain, fog, etc. than pulsed radar normally because it's easier to filter out the false returns with FMCW using digital processing. I suspect that's why the Navico isn't as good at picking out fronts and storm cells - it's filtering them out as false returns. Having said that FMCW can be better though, if the FMCW is too low a power then the signal will simply be attenuated by the rain or fog. This will reduce the range but also affect the sensitivity and resolution at the higher ranges but it should still better good at low ranges. The Navico 3G is a pretty low power device - I think the 4G is slightly higher power and better in this regard but I've never seen, one never mind used it in those conditions.

 

[Neeves]

This thread did make me ponder,

As implied we really get little or no fog, and it would be seldom we would sail then, we can wait maybe an hour and its all gone.

And then rain - there is rain and rain. I recall from the UK it could rain for hours and be miserable but the amount of rain that actually fell would not be much. Here it can rain for 10 minutes, and be equally miserable, and you cannot see 100m the rain is so heavy. In light rain, the type I recall would be more common in the UK Broadband is fine - in heavy torrential rain (storm cells) its no better than anything else.

We can see storm cells developing before they appear on our Broadband - but then they might be 20,000ft high and 20 nm away. Though you cannot differentiate individual storm cells by eye. Once they get closer you pick the individual cells up on BB but they merge, grow, disappear and its not until they are 2NM away you really know what guess to make.

4G is more powerful than 3G, reflected in power consumption, but the range is not that much better (inconsistently we could pick up cargo ships on 3G at 40nm but not low land at 10nm - so you could sail past a coral atoll and never see it on radar, it will pick up high coastal mountains) - but it might be better in rain (did not have time, nor opportunity, to try it). We use a 3G unit, we do not wish we had a 4G (but if we had a 4G would be equally happy).

For a yacht the original BR24 (2G) unit was good, as it had low power usage. I wish they had tweaked it a bit and had it and the 4G unit as with every new model the power has slowly risen.

Jonathan

 

[Ian_Rob]

Whilst the advantages of FMCW radar for sailing boats is clear, committing to it is another matter. My instinct is that a] 4G is about to become 5G [though I suspect that will be at the expense of a further hike in the power consumption] and b] that Raymarine, whose kit I already have, must surely enter the frame? Whilst a stand alone FMCW unit would have some attraction, you really need the display at the helm - which is impractical.

 

[Neeves]

I think everyone has been suggesting someone else will enter the FMCW fray for a couple of years, or more - it would be healthy. I'd have your fears about power for a 5G, though the instant 'on' and low power standby would remain.

Why is having the display at the helm impractical, expensive - yes but surely you could knock up something to make it possible? The big problem I see is that if you buy FMCW you have a screen that will do so much more (and you pay for it to be in the software when you buy it even if you do not need/want it) - but that is the same with any screen today.

The idea of common protocols has a little way to go

Jonathan