Furuno Plotter Overlay

DERF

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Following on from the problems I experienced with an ill installed Radar, I have another issue.

There is poor correlation between plotter/Radar overlay targets. The target echo(radar) is acurate, however the plotter- vs- vessel-target position is not.

The manual doesn't indicate how to offset plotter using overlay to align chart so it aligns with displayed radar target.

Anyone know the solution...jfm, mjf, ??
 

mjf

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well mine, on both helms tallies ok.

There is a an offset function in the set up - but because I have not needed it obviously have not climbed this particular learning curve.

maybe first we ought to check on your GPS. The radar range will be accurate so you need to assertain if you are indeed where the GPS thinks you are.
 

jfm

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Derf, is the misalignment angular or linear? If it's angular than your compass isn't fast enough and you need a gyro stabilsed heading sensor plugged intot he netwrk, not a normal fluxgate jobbie. If it's a linear offset/misalignment then I haven't got a clue though it is definitely a fault

I haven't used this stuff much. Magnum and tcm have it, they might know
 

tome

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Simple error which can cause exactly this problem is selecting the incorrect GPS datum- this should match the chart plotter. Is your position on the plotter accurate whilst alongside?
 

DERF

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Ok thanx for the replies.

Chart offset doesn't do it I've tried that.

The misalignment is linear not angular.

GPS using the correct datum.

At present plotter shows me bang on D14/15 which is where I am.

On the issue of offset, if I offset the plotter to correlate to the particular part of the solent I'm in at the mo, will that not then potentially cause a further offset problem eslewhere?

Surely I'll spend all my time resetting to default to make sure I'm where I think I am no?
 

tome

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Ok, then you can eliminate a datum problem.

How did you conclude that the radar display is accurate? And how far apart are your radar scanner and gps antenna?
 

DERF

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Radar targets appear where they should be, and using EBL and VRM and cross checking with set of rangefinder glasses its near as accurate as I could hope.

What happens is that I pass the target to beam, (and verifed by radar scan), but the plotter shows target ~3- 4 points off bow.

Scanner and GPS both on radar arch, bout 2 feet apart.
 

Ships_Cat

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Wild guess, is it boat speed related (assuming boat is fast)?

If target is relatively close and boat is fast might it be radar gives position as of the instant whereas GPS follows by some longer period of processing time - so in the case mentioned with radar showing target off the beam, plotter shows the same target displaced towards the bow.

Obviously easily checked - error disappears if slow or stopped. As I say, a wild guess.

John
 

DERF

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Very useful Tome thanx that link was extrmely useful. will try and see what I can achieve.

S.C. I don't think it is speed related as although I have set radar with auto speed offset it doesnt affect the overlay plot.
 

Ships_Cat

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Thanks for the comment back Derf.

I was not sure if there was auto compensation for speed or not for the overlay, although I assumed that there probably was. So I have learnt something. All the fast vessels I have been involved with are commercial and use separate ECS and radar with no overlay so correlation of the two is not an issue I have come across first hand.

John
 

DERF

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Tome,
Spent the weekend playing with the set up, tried every concievable option.

The only solution is to manually offset the chart plotter to compensate for the perceived error, so it does eventually match up with the radar image.

However if I am on plotter alone it then has me some 30 feet off the position that I am actually in.(cross checked with H/H Geonav)

So conclusuion is that the chart is in error and is no where near as accurate as I had thought.

It is probably the cartridge that I am using that is causing the problem.

I have reported this to C MAP today and awaiting a reply.


I still am unsure if I set up the plotter with offset to be correct in port solent, if I will be miles out in say Falmouth, or does it "auto compensate"...

Have asked this question of Furuno and C Map and will await a response.
 
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