steve930
Well-Known Member
I may well invest for my next boat then, it'd be a nice companion for nighttime cruising. Let alone foggy conditions etc
Do you know how your radar works?
- Thread starter paul salliss
- Start date
I may well invest for my next boat then, it'd be a nice companion for nighttime cruising. Let alone foggy conditions etc
D
Deleted User YDKXO
Guest
I always have the radar on when driving from the lower helm. For me it's a second pair of eyes which IMHO is necessary as the visibility is often somewhat obscured from down there. Also given the fact that one day you might have to rely on the radar in earnest, I think it's a good idea to use it regularly so that firstly you know that it is operating correctly and secondly, you get familiar with using it. You really don't want to be thumbing through the instruction manual trying to learn how it works when you unexpectedly find yourself in a peasouper in the middle of the Solent
MapisM
Well-Known Member
While fog is the scenario that is always mentioned in debates about radar usefulness, the worst case is actually heavy rain.
In fact, not only that can reduce the visibility as much as thick fog, but it takes much more than some fair weather practice to properly tune and understand a radar screen in the middle of a thunderstorm!
jfm
Well-Known Member
Paul, it would be well worth getting some tuition, and/or playing with it. Radar is totally fantastic. Makes night passages possible, and is nice bit of extra data even in good vis. I agree the comments that these days it functions mostly as collision avoidance, not nav, but that's fine. Hurricane's comment is, with respect, a bit 20 years ago: nowadays radars do much better angular measurement than in the olden days Mr Avis would be referring to, but angular accuracy isn't the critical feature anyways. The critical feature is showing a blob of some sort in front of you, so you don't hit it. And distinguishing between rain and hard objects
prv
Well-Known Member
That's interesting to hear, as I always understood it to be a physical limitation governed by the width of the scanner. So my dinky little 18" bar inside a plastic tub on the front of the mast will always throw out a wide and flabby beam giving imprecise blobby returns, whereas the 4 or 6 foot array on top of a boat like yours will give a neat pencil-like beam and well-defined targets. Have they got better at focussing a tight beam out of a short scanner?
Pete
Piers
Well-Known Member
It's all about the horizontal beam width, which on many leisure radars year ago was typically 4° or even more. This has reduced over the years ensuring the beam width becomes more and more accurate. OK, I have Furuno with a 6' scanner, but that has a beamwidth of 0.2°
So, distance accuracy, yes. Angular accuracy (nowadays), better and better. Once you accept this, it's down to how well it's lined up with your boat, how well you've tuned it (gain, sea clutter, rain brightness) and how well you've been trained. For example, do you set it Head Up, North Up, etc, and which offers what benefits. Fun. But, as I've said, once you've been on a good course (one day is fine) and then played with the set, you'll open a whole new world of electrickery.
It's the best mark one eyebal in fog and perfect for collision avoidance - provided you know what action to take.
Someone mentioned Pots and Gulls. Gulls are usually more easy to detect especially flocks of them which can frighten you in fog as they seem to target the boat and there you are taking avoiding action but they always turn with you! How many time have I done this....
Pots are harder to see, but if you tune the radar well you'll see them. Some are much more radar-visible, others aren't. Depends in the marker and flag material and if wet.
Robert Avis was the guru, but I'm sure some RYA radar courses and good.
End of my pet subject lecture....
Hurricane
Well-Known Member
I accept that radar electronics has become more accurate over the years.
But we have to remember that radar is driven and sensed by a mechanical device which will give rise to angular errors.
Additionally, for collision avoidance, MARPA relies on the accuracy of the ships heading sensor.
In my experience, the combination of these two parameters leads to a significant inaccuracy.
If you have AIS, you only have to look at the difference between the MARPA position and the AIS equivalent position.
I know it is easy to calibrate the two so that they match but then change your heading (say 180 degrees) and you will often see the calibration changes according to compass heading.
The distances to any target is exactly the same for a MARPA target to an AIS one so it has to be inaccuracies in the angular calibration.
The manuals always say choose good quality heading sensor and a a good locations for it to minimise these inaccuracies.
But the advice on here is to play with the kit on the passages where you don't actually need it - then you will trust it when you do actually need it (in fog - say)
But we have to remember that radar is driven and sensed by a mechanical device which will give rise to angular errors.
Additionally, for collision avoidance, MARPA relies on the accuracy of the ships heading sensor.
In my experience, the combination of these two parameters leads to a significant inaccuracy.
If you have AIS, you only have to look at the difference between the MARPA position and the AIS equivalent position.
I know it is easy to calibrate the two so that they match but then change your heading (say 180 degrees) and you will often see the calibration changes according to compass heading.
The distances to any target is exactly the same for a MARPA target to an AIS one so it has to be inaccuracies in the angular calibration.
The manuals always say choose good quality heading sensor and a a good locations for it to minimise these inaccuracies.
But the advice on here is to play with the kit on the passages where you don't actually need it - then you will trust it when you do actually need it (in fog - say)
MapisM
Well-Known Member
Sounds like your heading sensor could use a calibration, M.
I mean, not just by resetting the AIS/MARPA alignment, but rather making the 360° calibration, the one that with most sensor is done by turning slowly in large circles in flat waters.
In fact, from a mathematical/geometrical standpoint, II see no other reason why a target giving the same numbers on both MARPA and AIS should report something different after changing your heading, AOTBE. Aside from the numbers which inherently depend on your route obviously, like the CPA and TCPA.
D
Deleted User YDKXO
Guest
Actually jfm, it is Commander Robert Avis who sadly and prematurely died a few years ago. Robert was a both a Yachtmaster Examiner and Instructor and an expert on the use of radar at sea. He taught me for my Yachtmaster practical exam and I learnt more in the 3 days I spent with him on my boat than in the other 25 yrs I've been doing this boating lark. Top bloke too and excellent company
ashtead
Well-Known Member
Went on a good one day radar course yesterday and learnt lots not just about radar and margin used but also on use of hardware and now looking for a good book on topic ? Am aware of RYA text but any others worth considering?
Piers
Well-Known Member
One of the very best is written by Commander Robert Avis: http://www.amazon.com/Using-Radar-Practical-Guide-Small/dp/1574091050
And if you want to go one stage further: http://www.amazon.com/Superyacht-Master-Navigation-Robert-Avis/dp/0713664452
Piers
ashtead
Well-Known Member
Piers
Many thanks I will have a look as its a lot to take in on a one day course however it did help to show how raymarine buttons function and the raymarine tube vids also provide some illustrations of what can be achieved with dual display and overlay
Many thanks I will have a look as its a lot to take in on a one day course however it did help to show how raymarine buttons function and the raymarine tube vids also provide some illustrations of what can be achieved with dual display and overlay
Piers
Well-Known Member
Rovert certainly opened my eyes to the use of radar, and it came at a time when the thorny subject of whether your radar should be 'sea-stabilised' or 'ground stabilised' for use with MARPA. Deep stuff, but so helpful. You'll love the book. Robert had a way of making it all seem so easy - just how I need it!
paul salliss
Well-Known Member
. PM just sent
Solitaire
Well-Known Member
A couple of years ago I went on the bridge of a container ship on a trip to Le Havre. The radar was of course on and I asked the captain why no range rings etc. His comment was I dont want all the clutter that gets in the way! If I need to check anything I have the ERM and the EBL. He ran it North up.
I never run the overlay on the chart (apart from showing it to students) In fact I go so far as to say I hate it. To be honest I only use radar once outside the Solent when I am not teaching. I have used it for entry in the dark into Newtown for teaching purposes to demonstrate it as a pilotage tool. There is a real danger that the technology and what it can do overrides the real purpose of the kit. All IMHO of course!
Piers
Well-Known Member
Even though I have a commercial radar on Play d'eau (Furuno 2117 black box with 6′ open scanner) networked to a Furuno NavNet3D plotter, I, too, do not overlay one on the other.
I use EBL for accurate collision avaoidance rather than its extensive MARPA capability. Why? the EBL is the direct requivalant of the Mk1 eyeball.
I keep range rings on screen and run North Up (NU) so it always tallies with the chart plotter. Robert Avis demsontrated why NU was so important and I admit it took some getting to, but now I wouldn't change one little bit. I also use Trails (3 minutes worth) which I find invaluable.
Otter
Well-Known Member
Why not HU? Isn't that the equivalent of what you're seeing through the window?
Steve Clayton
Well-Known Member
I know how radar works including polar circulation to minimise rain effect, blind flying speeds and staggered PRF to eliminate same, H0 H1 etc waveguide calculations and effect of standing waves, purpose of a COHO oscillator, what the T/R switch does, amplification graph of a pentode, properties of the donkey's tool (seriously!!), stand on the duck boards, etc etc - mind you it was 30 years ago 
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Solitaire
Well-Known Member
From that question I guess you have your chart plotter H/U as well!
prv
Well-Known Member
I use radar-only mode for collision-avoidance, especially mid-Channel, because the picture is more detailed (my basic Raymarine set only uses one level of purple for radar returns in overlay mode) and the chart is irrelevant. But if you use radar for pilotage, it seems odd to me to forgo the overlay. The situational awareness is so much better, you can see everything that's either charted or radar-visible on one complete picture. And if the buoys and the coastline are lining up between radar and chart, you know that the GPS position is accurate and you can "drive the little boat across the map" in good conscience. It's like the old techniques involving drawing lines with a grease pencil and turning when things touch or line up, except that the "line" is an accurate representation of the coast and it doesn't need to be worked out in advance.
I too use the EBL, in my case because the MARPA is utterly crap
. The obvious limitation though is that you can only track as many targets as you have EBLs, in my case two. Does your Furuno allow more (or any number), or do you find that you only really need to keep an eye on one or two vessels at a time? My solution is to turn on the AIS overlay, and check that each radar return has an associated AIS target, then I only need to manually (with EBL) track any that don't. Pete
