Radar - Head up or Track up

[MartinGPerry]

I have always used my Radar with the display set to ships head up - that way if I see something at 10 oclock on the display I know to look 60 degrees of the bow it gets that info from the electronic compass available via NMEA from my autohelm

However following a rewire and addition of some new instruments, for some reason my radar will no longer display head up and will now only display track up even though heading info is still available on the NMEA bus.

This got me thinking about whether it would be better to use the track up display or fix the head up display

Most times I only use radar in fog or cross chanel cruising - when I see a ship on the horizon I place a bearing line on that ship, if it moves off the line then we are ok, if it comes down the line we are on a collission course - I have been doing for years this with head up display and it has worked well. However now I believe that this is wrong and this approach is only valid with a track up display.

When crossing the channel, my track could easily be 10 degrees off the heading due to tide and leeway

What do others think?








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[AndrewB]

Tide can normally be ignored when comparing your track with other moving vessels. So there won't be much difference between head and track up for collision avoidance, unless you are making considerable leeway. Its hard to believe that your radar won't show head-up, which doesn't need positional information, but will show track-up, which needs a GPS. Can't honestly say I've ever seen a track-up display.

 

[waterboy]

Hi Martin
It appears that as your radar is linked to the GPS you could also have North Up. This does take a little bit of getting used to but has some very good advantages. North up tends to give much steadier bearing angles when using your radar for navigation. It is almost impossible to hold a steady Course Up bearing unless the sea is dead calm. I believe most professionals use North Up these days.

<hr width=100% size=1>I never make the same mistake twice. I always make new ones.

 

[qsiv]

It also matches the presentation of most charts, so comparison with charted features is easier - however, to make it work you really need a reasonably high update rate from your compass - to all intents and purposes this would equate to a gyro with an update rate > 10Hz.

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[steve_cronin]

ANd.. if you're used to a plotter then north up seems much more familiar. If you're using a short range/small scale at night the way that the terrain whizzes around on the display not exactly in step with what you're actually doing, as you alter course in confined spaces, with head-up can be disconcerting too. You can easily mistake where a reef or shallow is for example.

Steve Cronin



<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[peterb]

I agree, I haven't seen a radar using "track up", either. But "course up" is quite common, and I suspect that that is what is meant here.

"Course up" usually means one or other of two things. In one, the display locks on to the heading at the moment of selecting "course up" mode, and keeps that bearing at the top of the screen irrespective of the heading. In the other, the top of the screen represents the course set on the autopilot; change the autopilot setting and the screen rotates. I have seen a third possibility, where the display is "head up", but on a long time constant so as to smooth out transient changes of heading.

Use of radar as an anti-collision tool is far easier if the display is locked to one bearing, either north-up or course-up. I suspect that part of the reason for the running down of 'Wahkunah' last year was that the crew were misled by a head-up display when their boat was stopped but turning in fog.

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[Oldhand]

If you really mean "track-up", this mode should not be used for collision aviodance. What matters is the relative motion in the water between your vessel and another vessel and your track over the ground has nothing to do with relative motion between the 2 vessels as seen on radar unless there is zero current.

On some radars, if "course-up" is selected and NMEA compass data isn't available but COG data is available, they will use the latter, which effectively gives the "track-up" you qoute. Such a feature is, in my opinion, an engineer's idea rather than a navigator's and shouldn't have been implemented as it can lead to erroneous collision interpretation of the radar display.

As already answered, "north-up" has become the favoured mode of radar operation as the compass input stabalises the display agaist "blurring" due to heading swings without compromising the correct relative motion display between your vessel and others. However, also as already answered, a 10Hz rate gyro enhanced compass input is really required to provide sufficient display stabilisation.

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[bedouin]

I don't think you get get North up from GPS alone. In order to get North Up you need to know the direction in which the boat is pointing, rather than the course over the ground, and GPS on its own can't give that.

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[Anthony]

Hi,

Maybe I am missing something here, but I dont understand the comment that track up should not be use for collision avoidence. Surely what matters is your path over the ground relative to the targets path over the ground, regardless of which direction either of you are pointing?

Can anyone please explain the reasoning behind why not to use track up display?

Thanks

Anthony

<hr width=100% size=1>The difference between men and boys, is just the price of their toys...

 

[Anthony]

Hi,

Maybe I am missing something here, but I dont understand the comment that track up should not be use for collision avoidence. Surely what matters is your path over the ground relative to the targets path over the ground, regardless of which direction either of you are pointing?

Can anyone please explain the reasoning behind why not to use track up display?

Thanks

Anthony

<hr width=100% size=1>The difference between men and boys, is just the price of their toys...

 

[jamesjermain]

...because you collide on the water not on the seabed (although you may well both end up there). Course-over-the ground (track) shouldn't be used for collision avoidance except in tideless waters when it is the same as course adjusted for leeway.

Howewver, in practical terms, the bottom line is that you need to take avoiding action if an echo is on a closing and steady bearing and this will show up whatever mode you use - you just have to work it out slightly differently.

My series on radar in YM will come to the question of collision avoidance and screen orientation later in the summer when I will go into this in more detail.

In short, though, if your set is capable and you have a heading reference, course up or north up are the best options for collision avoidance and if you are lucky enough to have MARPA (and it is well worth the money), north up is the answer.

<hr width=100% size=1>JJ

 

[Anthony]

Thanks, I look forward to reading the article and getting my head around it!

Anthony

<hr width=100% size=1>The difference between men and boys, is just the price of their toys...

 

[zefender]

I look forward to the article James. But will it be better if I read it with the pages North up or Head up?

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