Chart Plotter Position Error

L

LuckyLucy

New Member
Joined
12 May 2014
Messages
12
Visit site
My new SH CP180i give my coordinates on the visitor's birth at Fishguard lower harbour as:

51° 59' 52.26"N 4° 58' 1.75"W which is out by around 250m

Three other position sources that I have confirm that my position is in fact:

51° 59' 87"N 4° 58' 31"W

The plotter datum is set-up for WGS84

Why doesn't my new plotter know where I am?

Please tell me that I'm stupid and need to .............. (fill in as appropriate)..............
 
Are you sure it's not 51° 59.87N? That's about the same as 51° 59' 52.26"...i.e. one is decimal minutes, the other minutes & seconds?
Can't make sense of the westing, unless you mis-typed 17.5 seconds.
Suggest you change the display to decimal minutes and see how it compares.

P.S. PBO forum might also be a better setting for a question such as this...;)
 
Last edited:
Ok Changed format to ddd mm ss

Position is now given as:

51° 59' 52"N 4° 58' 19"W

It's impossible to tell with the basic map exactly where I am on the chart. I need to buy the C-MAP high resolution chart.
 
Remember that the accuracy of the digital chart is only as good as the paper chart it was derived from. Round the UK it should be good, but where I sail in Turkey the digital charts are based on paper charts that derive in the main from a mid 19th century survey by Captain (later Admiral) Beaufort of Beaufort Scale fame. Given the means at his disposal they are pretty good but in places the positions are wrong, so much so that my chart plotter shows me well ashore when moored in some harbours and on land when navigating one particular narrow channel.
 
You are in Fishguard
Maybe the topography is blocking the line of sight and your plotters can’t see enough satellites to get an accurate position.
 
Unless there's another Fishguard....

I bought the SH to replace my trusty NavMan. I've now mounted the NavMan next to the SH and taken a photo of their relative diplayed positions on the visitor's birth at Fishguard - everyone I speak to seems to think this is Fishguard, but who really knows?


Data Loggers.jpg
 
LuckyLucy: both are showing the same position.
The Navman is showing it in degrees and decimal minutes; the SH is showing it in degrees, minutes, seconds. You do not have a problem.

.873 is 52.38 seconds;
.314 is 18.84 seconds.

I suggest you decide which you prefer and set the new kit to that (FWIW my preference is for decimal minutes); but I suggest above all that you get your head around what each one means, since transferring the info to a paper chart, or vice versa, could give you serious problems.
 
Last edited:
There are lots of electronic charting errors some small, some large.
For example I found that your your track goes behind the lighthouse (over land) at the entrance to Porto Colom in Mallorca and if you head for Bagnara in Calabria you end up one mile south of the harbour entrance heading for a beach.
Lots more but the point is that you should double check with charts and pilot book.
PS: Raymarine chart plotter
 
Barnacle 1: sorry, only just spotted your post. The OP did reply to me by PM to say thanks, and that the 'problem' was simply down to different formats, as several had suggested. I agree that this would have been better posted on the open forum, if only for anyone seeking answers to a similar problem in years to come.

SHUG: the OP's problem was nothing to do with charting/datum errors, but simply minutes/seconds format.
 
macd said:
Barnacle 1: sorry, only just spotted your post. The OP did reply to me by PM to say thanks, and that the 'problem' was simply down to different formats, as several had suggested. I agree that this would have been better posted on the open forum, if only for anyone seeking answers to a similar problem in years to come.
Click to expand...
Right, I'm pleased about that and probably the other who had posted received a personal acknowledgement - except that shouldn't be how it's done, as you have commented.

I guess I had been disappointed a little too often how many post and never respond to help. This one followed hard on the heels of the lady with the Moody 42, she too disappeared without trace after many took the trouble to advise her.

C'est la vie. :D
 
Barnac1e said:
Right, I'm pleased about that and probably the other who had posted received a personal acknowledgement - except that shouldn't be how it's done, as you have commented.

I guess I had been disappointed a little too often how many post and never respond to help. This one followed hard on the heels of the lady with the Moody 42, she too disappeared without trace after many took the trouble to advise her.

C'est la vie. :D
Click to expand...

I quite agree (for all the invective these forums sometimes generate): I've always seen them as a resource, and a valuable one at that. Many posters, past and present, have contributed to my knowledge (others have simply made me laugh and sometimes despair, but mostly I've been at least entertained). I've no idea how ybw might best get across the message.
 
You must log in or register to reply here.

Share this page

Top