Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 17-03-2017, 05:23   #1
Registered User
 
epiic's Avatar

Join Date: Mar 2016
Location: Ottawa, Canada
Boat: Jeanneau 409
Posts: 246
C-Map Digital Charts for Bahamas are not accurate! :(

I was dead centre of these markers and as you can see, its off by quite a bit.

Did I waste $280???
Attached Thumbnails
Click image for larger version

Name:	c-map.jpg
Views:	527
Size:	390.8 KB
ID:	143321  
__________________

__________________
2015 Jeanneau Sun Odyssey 409 - 3 Cabin / 2 Head, Shoal Keel, Furling Main, Performance Genoa 135% with Tracks, Folding Prop, Bow Thruster, Air Conditioning, B&G Zeus2 Chartplotter, B&G Autopilot, B&G 4G Radar, B&G ForwardScan Sonar.
epiic is offline   Reply With Quote
Old 17-03-2017, 05:46   #2
Registered User

Join Date: Jun 2012
Location: Elmvale, Ontario
Boat: Ontario32
Posts: 160
Re: C-Map Digital Charts for Bahamas are not accurate! :(

Two different position reports on your screen shot. Were you running true or magnetic? Just asking.
__________________

Crew of Turning is offline   Reply With Quote
Old 17-03-2017, 05:58   #3
Registered User

Join Date: Nov 2007
Location: Probably in an anchorage or a boatyard..
Boat: Ebbtide 33' steel cutter
Posts: 4,460
Re: C-Map Digital Charts for Bahamas are not accurate! :(

Quote:
Originally Posted by epiic View Post
I was dead centre of these markers and as you can see, its off by quite a bit.

Did I waste $280???
A quick look at CM93 on openCPN has the charts about 0.25Nm off compared with google earth image so might be an accurate chart plotter but no accurate charts for there.
conachair is offline   Reply With Quote
Old 17-03-2017, 06:07   #4
Registered User

Join Date: May 2014
Boat: Morgan Out Island 41
Posts: 1,001
Images: 2
Re: C-Map Digital Charts for Bahamas are not accurate! :(

Quote:
Originally Posted by epiic View Post
I was dead centre of these markers and as you can see, its off by quite a bit.

Did I waste $280???
Keep in mind that GPS is not Accurate to zero feet. your chart plotter will tell you what the GPS accuracy is ( sometimes you need to add it to the display)

Navionics has a reputation for being much worse in the Bahamas (showing your track running straight through islands.
pcmm is offline   Reply With Quote
Old 17-03-2017, 06:24   #5
Registered User
 
epiic's Avatar

Join Date: Mar 2016
Location: Ottawa, Canada
Boat: Jeanneau 409
Posts: 246
Re: C-Map Digital Charts for Bahamas are not accurate! :(

Quote:
Originally Posted by Crew of Turning View Post
Two different position reports on your screen shot.
Yes. One is the position of my actual boat. The other is where you see the cross-hairs.

Quote:
Originally Posted by Crew of Turning View Post
Were you running true or magnetic? Just asking.
How would I find out? I thought GPS was GPS and did not vary like compasses do.
__________________
2015 Jeanneau Sun Odyssey 409 - 3 Cabin / 2 Head, Shoal Keel, Furling Main, Performance Genoa 135% with Tracks, Folding Prop, Bow Thruster, Air Conditioning, B&G Zeus2 Chartplotter, B&G Autopilot, B&G 4G Radar, B&G ForwardScan Sonar.
epiic is offline   Reply With Quote
Old 17-03-2017, 06:25   #6
Registered User
 
epiic's Avatar

Join Date: Mar 2016
Location: Ottawa, Canada
Boat: Jeanneau 409
Posts: 246
Re: C-Map Digital Charts for Bahamas are not accurate! :(

Quote:
Originally Posted by conachair View Post
A quick look at CM93 on openCPN has the charts about 0.25Nm off compared with google earth image so might be an accurate chart plotter but no accurate charts for there.
So then I did waste my money on these charts....
__________________
2015 Jeanneau Sun Odyssey 409 - 3 Cabin / 2 Head, Shoal Keel, Furling Main, Performance Genoa 135% with Tracks, Folding Prop, Bow Thruster, Air Conditioning, B&G Zeus2 Chartplotter, B&G Autopilot, B&G 4G Radar, B&G ForwardScan Sonar.
epiic is offline   Reply With Quote
Old 17-03-2017, 06:32   #7
Registered User

Join Date: Nov 2007
Location: Probably in an anchorage or a boatyard..
Boat: Ebbtide 33' steel cutter
Posts: 4,460
Re: C-Map Digital Charts for Bahamas are not accurate! :(

Quote:
Originally Posted by epiic View Post
So then I did waste my money on these charts....
They might be as good as it gets ........
conachair is offline   Reply With Quote
Old 17-03-2017, 07:04   #8
Registered User
 
epiic's Avatar

Join Date: Mar 2016
Location: Ottawa, Canada
Boat: Jeanneau 409
Posts: 246
Re: C-Map Digital Charts for Bahamas are not accurate! :(

Navionics on iPad had me dead centre of the buoys so I am really not impressed with C-Map.
__________________
2015 Jeanneau Sun Odyssey 409 - 3 Cabin / 2 Head, Shoal Keel, Furling Main, Performance Genoa 135% with Tracks, Folding Prop, Bow Thruster, Air Conditioning, B&G Zeus2 Chartplotter, B&G Autopilot, B&G 4G Radar, B&G ForwardScan Sonar.
epiic is offline   Reply With Quote
Old 17-03-2017, 07:09   #9
Registered User

Join Date: Aug 2014
Location: Astoria, NY
Boat: Sabre 38
Posts: 570
Re: C-Map Digital Charts for Bahamas are not accurate! :(

Maybe I'm being slow, but is your boat being shown off the map and the cursor is where you actually are? Plugging the coordinates into an online calculates says that those two points are 900 feet off. Quite a bit!

You using the Zeus GPS or an external?
__________________
Stephen

s/v Carpe Ventum
1983 Sabre 38
My Intro
fallingeggs is offline   Reply With Quote
Old 17-03-2017, 07:37   #10
Registered User
 
epiic's Avatar

Join Date: Mar 2016
Location: Ottawa, Canada
Boat: Jeanneau 409
Posts: 246
Re: C-Map Digital Charts for Bahamas are not accurate! :(

Quote:
Originally Posted by fallingeggs View Post
Maybe I'm being slow, but is your boat being shown off the map and the cursor is where you actually are? Plugging the coordinates into an online calculates says that those two points are 900 feet off. Quite a bit!

You using the Zeus GPS or an external?
My boat is off screen and I scrolled down to the obvious area to show how far off the charts are.

I am using a Zeus2 9" chartplotter
__________________
2015 Jeanneau Sun Odyssey 409 - 3 Cabin / 2 Head, Shoal Keel, Furling Main, Performance Genoa 135% with Tracks, Folding Prop, Bow Thruster, Air Conditioning, B&G Zeus2 Chartplotter, B&G Autopilot, B&G 4G Radar, B&G ForwardScan Sonar.
epiic is offline   Reply With Quote
Old 17-03-2017, 08:37   #11
Registered User
 
bvander's Avatar

Join Date: Jul 2004
Location: Maryland
Posts: 255
Re: C-Map Digital Charts for Bahamas are not accurate! :(

Been sailing Bahamas 8 years never had a problem. 2 years ago c map and Garmin both adopted Explorer chart data for Bahamas, so I believe all the datum is from Explorer, which most everyone cobuilders the gold standard for Bahamas.
bvander is offline   Reply With Quote
Old 17-03-2017, 08:53   #12
Registered User

Join Date: Aug 2015
Location: SW Florida
Boat: Grand Banks 49
Posts: 521
Re: C-Map Digital Charts for Bahamas are not accurate! :(

Quote:
Originally Posted by epiic View Post
I was dead centre of these markers and as you can see, its off by quite a bit.

Did I waste $280???
===

C-map charting on my Furuno GPS/plotter has always been very accurate in the Bahamas. Is this a one-time issue or are you seeing consistent errors of a similar magnitude? If so, check your plotter options to make sure you're using the correct datum and ensure you don't have any offsets entered.
wayne.b is offline   Reply With Quote
Old 17-03-2017, 09:02   #13
Registered User

Join Date: Feb 2017
Posts: 33
Re: C-Map Digital Charts for Bahamas are not accurate! :(

Quote:
Originally Posted by epiic View Post

How would I find out? I thought GPS was GPS and did not vary like compasses do.

You can sett GPS True, Magnetic or Grid North.
royalstar is offline   Reply With Quote
Old 17-03-2017, 09:20   #14
Senior Cruiser
 
Captain Bill's Avatar

Cruisers Forum Supporter

Join Date: Apr 2008
Location: On the boat
Boat: Endeavourcat Sailcat 44
Posts: 2,583
Re: C-Map Digital Charts for Bahamas are not accurate! :(

Sometimes it has more to do with differences in the software that draws the chart. I have the cmap charts in my chartplotter and on a laptop running Coastal Explorer. One has me in the center of the channel and the other one has me clearly outside the channel. I never trust the chartplotter to go into a channel for the first time. I find that if it renders it properly once it is consistent and I'm willing to chance it at night, but never ever the first time. I also find that if it has rendered it improperly it is also consistent and I never will go in that channel using the GPS.
Captain Bill is offline   Reply With Quote
Old 17-03-2017, 09:38   #15
Registered User

Join Date: Sep 2013
Location: Montreal
Boat: Dufour 39 Frers
Posts: 269
Re: C-Map Digital Charts for Bahamas are not accurate! :(

Modern all-singing all-dancing MFD device make the data look so damned cool that it’s just human nature to forget that display technology has absolutely NOTHING to do with accuracy.

"How to read Nautical charts" from Nigel Calder is a book everybody should read and reread...

Your GPS is probably on WGS84 datum , but are you sure ? Did you check that ?

Your map may be on a different datum. I am sure you have verified that too?

Have you check the scale of the map ? May be you are over zooming ? Accuracy of drawing on a map at 1:40000 is 1 mm. This correspond to 40 meters on the ground, or 120 feet. This is half of your screen at the 200 feet zoom setting...

So, a map with a 1:40000 scale has a drawing precision of 120ft. Your GPS says its precision is 4m 12 feet. How do you deal with that ?

1% of the area where sounding are less than 200 meters are considerate accurate in the Bahamas. 99% is considerred needing re-survey.

Welcome to the real world.
__________________

Emouchet is offline   Reply With Quote
Reply

Tags
Bahamas, charts, c-map

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
Clamp ammeters: accurate or not? 44'cruisingcat Electrical: Batteries, Generators & Solar 13 15-07-2016 14:57
Mastervolt BTM-iii not accurate YoloSF Electrical: Batteries, Generators & Solar 18 06-01-2016 09:51
iNavX charts for accurate Mx plotting ? SvenG Navigation 0 09-08-2013 19:24
Floscan not accurate Delfin Powered Boats 0 06-07-2013 18:17
Want To Buy: C Map NT+ (not C Map Max) ianca Classifieds Archive 0 21-02-2013 04:10



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 20:47.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.