Chartplotter losing fix

maxcampbell

maxcampbell

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Me - village in south cambs. Boat - Brightlingsea
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I've got a Raymarine RC400 chartplotter (ie the 5" screen one). It's mounted on the aft end of the cabin, near the top, outside.

How can I minimise the possibility of it losing its fix?

Is it possible to rig an external antenna?

What conditions (including weather) lead to more fix losses?

It always seems to re-find itself quicker if I switch off then on again - am I kidding myself or is there a good reason for this?

Typically in a 5 or 6 hour sail it will lose a fix 3 or 4 times, but a couple of days ago it would only maintain a fix for 30 or 40 minutes. It was raining, and I was in an area where I haven't noticed a particular problem before.
 
maxcampbell said:
I've got a Raymarine RC400 chartplotter (ie the 5" screen one). It's mounted on the aft end of the cabin, near the top, outside.

How can I minimise the possibility of it losing its fix?

Is it possible to rig an external antenna?

What conditions (including weather) lead to more fix losses?

It always seems to re-find itself quicker if I switch off then on again - am I kidding myself or is there a good reason for this?

Typically in a 5 or 6 hour sail it will lose a fix 3 or 4 times, but a couple of days ago it would only maintain a fix for 30 or 40 minutes. It was raining, and I was in an area where I haven't noticed a particular problem before.
Click to expand...

are your settings on 2d or 3d fixs
 
Is anyone sitting above the antenna when you lose the fix? this is quite common with deck mounted mushroom antennas but it may also be an issue with built in ones if someone sits above it.
Cheers
Dave
 
I don't think it's possible to choose between 2D and 3D positioning, or to fit an external antenna with the RC400.
There is a GPS set-up page, which shows satellite status, including signal strength for up to 12 satellites.
I would suggest moving the plotter to various positions and seeing if the usual position gives as good reception as anywhere else.
My RC400 performs OK inside the cabin, but better with a clear view of the sky. Since I don't use it all that often, I can't really say if rain affects it, although I've not noticed any effect on my Furuno GPS, which seems to have been in the rain all too often!
 
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It really should not be necessary to do anything in order to get a stable fix - I would be suspicious of the plotter. You don't make clear what kind of boat it is installed in, but the GPS signal will pass through substantial thicknesses of GRP with little attenuation - we have a Lowrance HDS5 installed inside the boat at the chart table and the lock is rock solid. The GPS carrier frequency is chosen to be relatively resistent to rain, so it would take a torrential downpour to drop the signal to levels that would lose the lock.

Where are you sailing? While the theoretical coverage is worldwide, the constellation is often biased towards the equatorial belt and reception at high latitudes can be reduced sometimes.
 
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The chartplotter is outside on the port cabin end. If I can post an image I will, but the boat (wood) is in my avatar, and videos of her in my signature link. There's a clear view of the sky, and I can't see anything that could interfere with a signal.

I sail on the East Coast of England.
 
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Even if it were inside a wooden boat, you should not have siginficant problems getting a lock. When I was testing my Lowrance prior to fitting, I was getting a reasonable lock with the plotter in the kitchen. Can you get a satellite status display up? That might help to see if there are any significant blind spots due to screening by some component of the boat.

I still think you most likely have a fault on the plotter - modern GPS receivers are so sensitive that they will get a fix with very low signal levels.
 
Were you anywhere near a wind farm? My Raymarine plotter sometimes loses course and then fix information within a mile or so of one, but my Garmin hasn't so far been affected.
 
pic here sorry can't post pic itselfhttp://flic.kr/p/bWf6HY

PeterBoater said:
Were you anywhere near a wind farm? My Raymarine plotter sometimes loses course and then fix information within a mile or so of one, but my Garmin hasn't so far been affected.
Click to expand...

I was very close to the Gunfleet sands windfarm when it wouldn't hold a fix for more than 30 minutes, but every day it loses a fix a few times.

I have accepted occasional fix losses as par from the course until now, but everyone asserting that they don't get these has led me to re-read the manual. The unit is barely the recommended 3' from the VHF - does the panel think this is likely to be significant? God knows where I move either to, but I will try sailing with the radio switched off next time.
 
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maby said:
Where are you sailing? While the theoretical coverage is worldwide, the constellation is often biased towards the equatorial belt and reception at high latitudes can be reduced sometimes.
Click to expand...

Not true - the height of the satellites is such that polar visibility is just as good, and the geometry sometimes better because of "over the Pole" lines of sight. The only problem in polar regions can be because satellites are often low in the sky, and steep terrain can mask them.

sailorman said:
are your settings on 2d or 3d fixs
Click to expand...

It doesn't make a lot of difference - you need three satellites for a 2D fix, and 4 or more for a 3D one. These days, if you aren't seeing at least 6 satellites, there is something wrong, especially at sea with a clear view all round. Incidentally, a 2D fix can be a lot less accurate than a 3D one.

I'd ask if there are any substantial lumps of metal near the unit that are shadowing a significant part of the sky from the receiver. Mast steps, wiring looms, rigging or whatever.
 
AntarcticPilot said:
Not true -...
The only problem in polar regions can be because satellites are often low in the sky, and steep terrain can mask them.

....
Click to expand...

I think that is what I said, isn't it? Most GPS receivers are programmed to discount low elevation satelllites because they are more vulnerable to atmospheric path distortion.
 
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lw395 said:
. . . A Garmin GPS may be your best bet.
Click to expand...

:D

Joking apart, a question that has not been asked is, have you changed, installed, modified any electronic equipment since it last worked satisfactorily?

Have you installed or modified any metal surfaces near the equipment or antenna, including thermal lagging?

Do you run a computer near the chartplotter?

If not, then possibly the equipment has faulty circuitry and only two circuits that receive the ~1600MHz satellite signals is working, possibly a dry joint on the internal pcb rx board?

Get yourself a Garmin. :D
 
maby said:
I think that is what I said, isn't it? Most GPS receivers are programmed to discount low elevation satelllites because they are more vulnerable to atmospheric path distortion.
Click to expand...

They are usually higher than that limit, even in the Polar regions. For marine use, and even on the vast majority of the continent (where surface slopes are remarkably low), this is not a constraint, and as I mentioned, because of "over the Pole" lines of sight, you can often get better geometries than in temperate regions. Since the constellation of satellites was completed, there have been no constraints on the use of GPS in the Polar regions, and my colleagues routinely used it for surveying to centimetre accuracy (using post-processing). Millimetre accuracy as attainable, but only using special equipment.
 
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