RADAR DISPLAYS

[Marsupial]

Some questions to ponder over. . . .

You are crossing the Dover Strait towards Dover from say Abbeville, the spring tide is ebbing, Your Heading is 278degM your Course Over Ground is 302degM.

If you switch your RADAR to display Head UP what do you expect to see? (in terms of the orientation of the display relative to the boat)

If you switch to Course Up what would you expect to be different? (if anything)

Finally in the scenario above what is best display for collision avoidance?

Your views (sorry!) on this would be appreciated.


Cheers

David

 

[Talbot]

The selction will really depend on how your radar is connected, what instruments you have, and what NMEA sentences the radar uses.

If it is simplistic, just taking COG from GPS, then top of the display will be 302 degrees presumably from course up and 278 head up, but expect that yours may read other sentences so you really need to read the manual! /forums/images/graemlins/wink.gif

 

[john_morris_uk]

I don't understand the difference between Course up and Head up in Radar terms. It seems very strange that you have the option of switching to COG up in your Radar display and I can't imagine many situations in which it would be useful. (I suppose you could use it for navigation in some circumstances, but it would not be my preferred option..

Normally the two different displays available on a Radar are 'North Up' and 'Head Up'. Most people find ships Head Up easier to use for collison avoidance. Unless you have a gyro or electronic fluxgate compass supplying data to your Radar, you won't have North up as an option.

Reference the tide, all vessels are being affected by the same tidal stream, so it is irrelevant. For collision avoidance you are concerned with the relative speed and bearing of the other vessel to you.

 

[Robin]

You will 'see' exactly the same whichever you choose EXCEPT that each target will be in a different position on the screen depending on if you set Head Up or Course Up or if your set allows North Up.

For collision avoidance IMO I would always use Head Up, ie the radar heading mark is aligned looking straight ahead where the boat is pointing and where I would be looking in clear vis with mark one eyeball. Radar however is all about relative motion and the target you hit is one that comes down any constant bearing line, not just and even rarely the one that is dead ahead in line with the boat (at any distance at least).

Is this a trick question or a genuine one? If the latter I might tactfully suggest some reading of a Radar instruction book and some regular practice in clear visibilty until you have some confidence. It isn't as difficult as it seems or as it is to describe! Sorry if it seems patronising, it isn't intended to be.

 

[Marsupial]

Robin

No its not a trick and no offence taken.

Other posters have described what I believe should be happening when the radar is connected to a course computer fed with course and heading information electronic compasses and the like. The JRC and Furuno systems do behave the way described (and you dont get a choice unless you switch off the NMEA data) On these sets Head up would be 278 in the senerio above, course up 302. So in course up mode the radar shows where the boat is actually going not where its pointing. This is not so with the raymarine system its always head up.

I have been using RADAR for about 20 years, but have recently changed to RAYMARINE. I shall just keep away from the C-UP mode.

Thanks for the comments.


David

 

[fireball]

So - what do you use if you have RADAR overlayed on a chart?

For most (men anyway) it is usual to have the chart NorthUp ...
For RADAR it seems to be most common to have Headup Display ...

So - when overlayed on the same screen - which one do you use?

 

[Marsupial]

Fireball

I dont use the radar and chart potter to overlay - although the system will do it - because the screens (7inch on my system) are IMHO far too small to be useful, I interface with a Yeoman plotter for naviagtion and target plotting. The radar is for collision avoidance and the EBL is IMHO the best feature next to MARPA. Most of the time the system displays the highway and a few important numbers.

Yes, strange but true, I still draw lines on charts and I dont mind which way up it is.

SWMBO on the other hand like some women (no offence ladies) has a magnetic nose so north is a constantly movable concept so for her at least North is synonymous with Course Up!

The yeoman sport is easy to rotate it works any way up, so its not an issue as long as the correct charts are properly referenced. Most of the time every one is happy!

 

[Robin]

David

Sorry I had s sneaky suspicion it was a Yachtmaster class question!

On our last boat I initially fitted a Vigil, only came with head up and not even daylight viewing. Later this was changed to a superb Furuno CRT display bigger screen model and 24ml range but again only had the head up option (though could display magnetic rather than relative bearings IF fitted with the Furuno electronic compass, ours wasn't and the Raymarine compass wouldn't work this option even via NMEA).

Our current boat has a very basic Raymarine LCD set but we can display EBLs as relative or magnetic (and HAVE to display them as magnetic if we use the waypoint lollipop feature). Course up isn't an option on this radar even though it has the data to produce it from Seatalk and/or NMEA. We have standalone plotters and overlaying isn't an option, plus like you I believe the screens are too small for this to be worthwhile anyway.

I'm probably a phillistine but I wouldn't trust MARPA at all unless it was via a very fast and very stable compass input, not the fluxgate from the autopilot!

Robin

 

[pvb]

Your system is working as intended...

I think you'll find that your Raymarine system is working as it's intended to. When "Course Up" is selected, the course used is the locked heading from the autopilot, not the course from the COG output from the GPS. That's probably why you think it's not working properly.

The newer C-series uses slightly different criteria for operating in Course Up mode.

 

[peterb]

Re: Your system is working as intended...

[ QUOTE ]
When "Course Up" is selected, the course used is the locked heading from the autopilot, not the course from the COG output from the GPS.

[/ QUOTE ]

You're certainly right that the course used is that locked on the autopilot, but what about when the autopilot is not in use? It's a year or so since I used a Raymarine radar, but I seem to remember that the course used is then the heading at the moment that the 'course-up' mode is chosen.

I remember that the coure-up mode was very useful. It gave the benefit of the head-up mode in that the display agreed better with the picture seen from the cockpit, while retaining the north-up mode's advantage of a stabilised display.

Be careful with collision avoidance in head-up mode. Any change of heading causes the whole display to rotate, making it difficult to estimate collision risk.

 

[pvb]

Yes...

Yes, with the older Raymarine units, if the autopilot isn't in use, the "Course Up" mode uses the actual heading when Course Up was selected.

 

[Marsupial]

Re: Yes...

Thanks for that everyone.

Iam sure the thing is working correctly but I dont agree with the raymarine definition of course up in this implemetation. The way the system behaves is not intuitive as demonstarted by the posts above.

Certainly the lack of a course up display based on COG is a slight issue when using the radar as navigation aid, my crew are used to seeing the target waypoint on the "lubbers line" and "aiming at it" - not a problem with carefully selected waypoints - but not possible with this system!

Be wary of C-UP on Rayamrine Systems, reading the book for each implemetation is vital.

Cheers



David