Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 27-03-2023, 12:20   #1
Registered User

Join Date: Mar 2023
Posts: 2
Open CPN inconsistent with Paper Charts

I've just started using Open CPN on a Mac with OS Catalina version 10.15.7. There was no problem with creating waypoints and routes between San Pedro Harbor and Catalina Island, but I ended up with inconsistencies between what was listed on my route printout for courses between waypoints and what was described when placing the cursor over the legs on the digital chart.
Also, when checking leg courses between the digital chart and Paper chart,
(Maptech #129, Los Angeles & Santa Monica Bay), I found major inconsistencies on course directions. I thought perhaps I wasn't calculating magnetic variations accurately, but found that "True" courses were different as well. Even a plotted position ended up being slightly different on the digital chart compared to the paper position - .4'.
Any suggestions?
Much Appreciated,
Twisted Kilt 2
Twisted Kilt2 is offline   Reply With Quote
Old 27-03-2023, 12:29   #2
bcn
Registered User

Join Date: May 2011
Location: underway whenever possible
Boat: Rangeboat 39
Posts: 4,795
Re: Open CPN inconsistent with Paper Charts

Which digital chart? RNC or ENC?
Screen shots to understand your findings?
Why do you think that the paper solution is the correct one? What are the differences in degrees? Or tenth of degrees? How do you measure the true course?
bcn is offline   Reply With Quote
Old 27-03-2023, 12:56   #3
Registered User

Join Date: Mar 2016
Location: San Francisco
Boat: Morgan 382
Posts: 3,120
Re: Open CPN inconsistent with Paper Charts

If you are using NOAA charts. Paper charts haven't been updated in a while. This would include "Maptech" branded charts that are printed from official charts. RNC electronic charts are made from the paper charts, and could be expected to be dated as well. The ENC is the current and updated chart. So, if you find discrepancies, the ENC is likely the most correct.

I don't specifically understand what your inconsistencies are, however. Screenshots or examples would help.
__________________
-Warren
wholybee is offline   Reply With Quote
Old 27-03-2023, 14:11   #4
Registered User

Join Date: Mar 2023
Posts: 2
Re: Open CPN inconsistent with Paper Charts

Thanks Warren. RNC is the chart currently on my desktop, so I guess I need to figure out how to get the ENC versions up. The compass rose on the RNC chart is consistent with the directions given on the the course legs. Two paper charts I have, one the Maptech and another, an old NOAA of the San Pedro Channel still show differences of about 4 degrees True, which doesn't make sense to me. I'd like to be able to have backup paper in the event that the electronics fail, but I guess I need to get the most current NOAA versions before I start plotting courses from the CPN charts.
Much appreciated,
Mark
Twisted Kilt2 is offline   Reply With Quote
Old 27-03-2023, 14:24   #5
Registered User

Join Date: Mar 2016
Location: San Francisco
Boat: Morgan 382
Posts: 3,120
Re: Open CPN inconsistent with Paper Charts

You can download ENC charts in the chart downloader plugin.

I would expect paper and RNC charts of the California coast to all be pretty accurate. But what you might be seeing is that electronic navigation is just more accurate than what you are used to.

What are the issue dates on the paper charts?
__________________
-Warren
wholybee is offline   Reply With Quote
Old 27-03-2023, 14:43   #6
Registered User

Join Date: Jun 2022
Location: Cantabria
Boat: Jeanneau - Merry Fisher 925
Posts: 497
Re: Open CPN inconsistent with Paper Charts

Have you check if NOAA charts have been printed on WGS84 datum or any of the multiple American Datums?

You should know that if they have been produced with a different datum than WGS84 all plotted position should be shifted in a quantity stated & printed in the chart itself.
__________________
Corsair

Roses don't bloom on the sailor's grave
Corsair63 is offline   Reply With Quote
Old 27-03-2023, 14:54   #7
Registered User

Join Date: Jun 2022
Location: Cantabria
Boat: Jeanneau - Merry Fisher 925
Posts: 497
Re: Open CPN inconsistent with Paper Charts

Also bear in mind that most of the profesional GNSS receivers have the selection of the Datum that you want to use, supposed by default they have activated WGS84, but if you have been using another one to be agreed with the paper charts and not making the correction, now when you want to plot directly , you'll have to switch again to WGS84.
Attached Thumbnails
Click image for larger version

Name:	sshot-2.jpg
Views:	65
Size:	430.7 KB
ID:	273382  
__________________
Corsair

Roses don't bloom on the sailor's grave
Corsair63 is offline   Reply With Quote
Old 30-03-2023, 09:31   #8
Registered User
 
rooiedirk's Avatar

Join Date: Aug 2010
Location: Netherlands
Boat: Oneoff
Posts: 514
Re: Open CPN inconsistent with Paper Charts

Seems indeed that there are small differeces. I guess rounding errors.
__________________
Navigation is know where you are and what to do to get where you want.
But also: Know where you don't want to be and what to do to don't get there.
rooiedirk is offline   Reply With Quote
Reply

Tags
charts, open cpn

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Trying to find a fridge issue with inconsistent function SailorMcCruise Plumbing Systems and Fixtures 25 27-05-2019 11:11
Maggi metric chain non-standardized inconsistent sizing sailabroad Anchoring & Mooring 0 11-08-2016 14:17
Inconsistent ammeter & alternator macbeth Electrical: Batteries, Generators & Solar 6 23-07-2012 07:17
Damn Paper Charts . . . I Hate Paper Charts ! off-the-grid Navigation 84 20-03-2011 15:20
Inconsistent Idle theonecalledtom Engines and Propulsion Systems 6 22-11-2010 00:23

Advertise Here


All times are GMT -7. The time now is 19:16.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.