Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 27-05-2018, 10:29   #1
Registered User
 
martinworswick's Avatar

Join Date: Sep 2008
Location: southern denmark
Boat: naver 29
Posts: 146
chart differences

My onboard plotter is a raymarine rc435 and i knew my position was quite a way off-it shows me in openwater when i'm tied in my slip,i thought i'd compare it to bing maps in ovitalmap on an ipad and a ge2kap chart in opencpn on a rpi-the coloured dots i've made are my estimates of the position of the gps receiver
Attached Thumbnails
Click image for larger version

Name:	raymarine.jpg
Views:	45
Size:	394.7 KB
ID:	170606   Click image for larger version

Name:	ovital.jpg
Views:	47
Size:	400.9 KB
ID:	170607  

Click image for larger version

Name:	opencpn.jpg
Views:	49
Size:	406.1 KB
ID:	170608  
__________________

martinworswick is offline   Reply With Quote
Old 27-05-2018, 10:38   #2
Senior Cruiser
 
Steadman Uhlich's Avatar

Cruisers Forum Supporter

Join Date: Jul 2014
Location: Crewing All of 2018 Available Globally
Boat: OPB = Available as Crew in 2018
Posts: 5,709
Re: chart differences

Verrrry interesting!

Thanks for posting the comparison.

I recently sailed up Penobscot Bay Maine, and compared what I saw on a Raymarine Chartplotter (recent model, large hybrid touch screen) with what I saw on an iPad next to it, that has SEAiq on it.

It seemed to me that the SEAiq chart and IPad GPS position of our boat was more accurate to what I observed with my eyes on the passing landmarks on the many small islands and ATONS, though I did not do have any screengrabs and did not take photos to show, but I now wish I had. What I recall was it appeared to be a striking difference.

I am sorry I cannot provide more details, as I do not own the gear and I am off the boat after the voyage ended a few days ago.
__________________

__________________
Ahoy All Sailors! Need experienced crew for a passage or delivery in Atlantic, Pacific, Caribbean, Med, PNW, ICW, coastal or across an ocean anytime in 2018? I am available on 24hr notice. See my CF Profile "About Me" page for details. Happy to lend a hand!
Steadman Uhlich is online now   Reply With Quote
Old 27-05-2018, 12:10   #3
Registered User
 
CaptTom's Avatar

Join Date: Apr 2004
Location: Southern Maine
Boat: Prairie 36 Coastal Cruiser
Posts: 1,226
Re: chart differences

Older chartplotters sometimes defaulted to a different datum. It's also possible to inadvertently change the datum. This will cause everything to be in the wrong position.

There should be a page which shows HDOP (horizontal dilution of precision) or just DOP. Nowadays expect that number to be not muich more than a couple of meters (half-dozen feet.) If that number is small, and you're using the right datum, just about any chartplotter ever made should put you very close to exactly the correct location, unless you're in an area that's not well charted, like some inland canals in the US and Canada, or some remote islands.
CaptTom is offline   Reply With Quote
Old 27-05-2018, 12:22   #4
Registered User
 
martinworswick's Avatar

Join Date: Sep 2008
Location: southern denmark
Boat: naver 29
Posts: 146
Re: chart differences

Quote:
Originally Posted by CaptTom View Post
Older chartplotters sometimes defaulted to a different datum. It's also possible to inadvertently change the datum. This will cause everything to be in the wrong position.

There should be a page which shows HDOP (horizontal dilution of precision) or just DOP. Nowadays expect that number to be not muich more than a couple of meters (half-dozen feet.) If that number is small, and you're using the right datum, just about any chartplotter ever made should put you very close to exactly the correct location, unless you're in an area that's not well charted, like some inland canals in the US and Canada, or some remote islands.
i'll check that next weekend,its been that way ever since i bought the boat-assuming the previous owner had it all set correctly could be a mistake i suppose....
martinworswick is offline   Reply With Quote
Reply

Tags
enc

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
NADA, BUC and Boat List Price Differences? seacurves Dollars & Cents 38 01-11-2017 09:14
Differences in Marine and RV Inverters / Chargers clubhouse Electrical: Batteries, Generators & Solar 7 23-03-2010 14:23
Any Significant Differences Among these Boats? divelly Monohull Sailboats 15 14-10-2009 17:20
Anchor Chain size differences svmariane Anchoring & Mooring 8 16-07-2007 23:40



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 12:55.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.