Chart Plotter Accuracy - Be Careful - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > General Interest > General Discussion (sailing related)
 Not a Member? 


Reply
 
LinkBack Thread Tools
  #1  
Old 06-14-2010
Senior Member
 
Join Date: Dec 2008
Location: North Carolina
Posts: 583
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 6
NCC320 is on a distinguished road
Chart Plotter Accuracy - Be Careful

My neighbor just came back from a cruise in NC waters that took him up the Alligator River. He told me that he met the crew of a Catalina 42 that was using a chartplotter to navigate and ran aground in the river because the electronic chart failed to show a shoal that was clearly shown on the paper charts. After losing several hours trying to kedge off, wherein the captain badly hurt his hand on the anchor chain, the boat was towed off the shoal at the cost of $1,800. My neighbor, who also has a electronic chart plotter, confirmed that the shoal was not shown on his electronic charts either (don't know if the two plotters were the same make, nor which makes). He confirmed that the paper charts showed the shoal clearly. Just a note of caution, the computer is not always correct.

Last edited by NCC320; 06-14-2010 at 12:14 PM.
Reply With Quote Quick reply to this message Share with Facebook
  #2  
Old 06-14-2010
Vasco's Avatar
Warm Weather Sailor
 
Join Date: Sep 2006
Location: Toronto
Posts: 989
Thanks: 0
Thanked 6 Times in 6 Posts
Rep Power: 9
Vasco is on a distinguished road
Why would anyone rely on a chartplotter in these waters? The ICW marks are very good in the river. And if you're venturing out of the channel you really have to watch the depth sounder carefully. No chart can be relied upon. The depths change frequently and the waters are certainly not surveyed annually.

If you really want to see inaccurate electronic charts try the Bahamas and Navionics charts. Their charts will take you over the tops of islands (if you're dumb enough to rely on them).
__________________
Rick I
Toronto in summer, Bahamas in winter.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Quick reply to this message Share with Facebook
  #3  
Old 06-14-2010
Junior Member
 
Join Date: Feb 2005
Posts: 5
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
PA28235Pilot is on a distinguished road
Total reliance on a chartplotter is as big a mistake as total reliance on a printed chart.

It is not correct to imply that chartplotters can be inaccurate and charts are not. It may be true in this case but leaving out variables such as the age of the chart vs the age of the chartplotter databases makes any comparison useless. I've seen inaccuracies in both.

I'd rather take information from as many sources as reasonable, including eyeballs, depth sounder, radar etc., and combine them to make course decisions.
Reply With Quote Quick reply to this message Share with Facebook
  #4  
Old 06-14-2010
RichH's Avatar
Senior Member
 
Join Date: Jul 2000
Location: Pennsylvania
Posts: 2,930
Thanks: 9
Thanked 78 Times in 71 Posts
Rep Power: 15
RichH will become famous soon enough
Its EASY to get in trouble with a chartplotter.
Especially when using HIGH mignifications ... called 'resolution error' - using inappropriate 'magnifications' based on old survey data that was established with sextants, theodolites, 'chains', etc.
An example of a 'resolution error' would be driving an automobile while looking through a very highpower binocular.

Plus, moving/shifiting bottoms, newly forming shoals, recent changes of the 'marks', etc. simply arent 'automatically' updated on chartplotters. I do a lot of long distance cruising and have the 'gut-feel' that the best chartplotter with the latest software is only accurate about 90% of the time (and when operating on 'medium' magnifications values.)
Reply With Quote Quick reply to this message Share with Facebook
  #5  
Old 06-14-2010
Yorksailor's Avatar
Senior Member
 
Join Date: Oct 2009
Location: Pacific side of Panama
Posts: 497
Thanks: 16
Thanked 20 Times in 19 Posts
Rep Power: 6
Yorksailor is on a distinguished road
We entered Spanish Waters in Curacao recently and the chart plotter showed us to be in the Hyatt hotel swimming pool...

The Bahamas have not been surveyed since the Brits left 30-40 yrs ago so why would anyone think the charts might be accurate.

Rich is absolutely right...higher magnifications just increase the delusional nature of believing chart plotters.

# 1 eyeball at all times in restricted waters and preferably with a high sun over your shoulder!!!
Reply With Quote Quick reply to this message Share with Facebook
  #6  
Old 06-14-2010
Senior Member
 
Join Date: Jun 2006
Posts: 4,999
Thanks: 5
Thanked 18 Times in 18 Posts
Rep Power: 11
wind_magic has a spectacular aura about wind_magic has a spectacular aura about wind_magic has a spectacular aura about
In some ways the raster charts are even better than the vector charts, at least with the raster charts when you magnify them too much they get blocky, but if you magnify those vector charts they have that nice clean edge no matter how big you make them.

I think part of the danger with chart plotters is just a kind of techno-faith people seem to have, they put a certain amount of belief in it just because it is an electronic gadget.
__________________
What are you pretending not to know ?

Please support my
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Quick reply to this message Share with Facebook
  #7  
Old 06-14-2010
Vasco's Avatar
Warm Weather Sailor
 
Join Date: Sep 2006
Location: Toronto
Posts: 989
Thanks: 0
Thanked 6 Times in 6 Posts
Rep Power: 9
Vasco is on a distinguished road
Quote:
Originally Posted by Yorksailor View Post
The Bahamas have not been surveyed since the Brits left 30-40 yrs ago so why would anyone think the charts might be accurate.
Wrong! The Bahamas have been surveyed extensively in the past few years and the Explorer Charts are very accurate. However you still need to use your eyes and proper seamanship! Prior to the Explorer Charts some of the Admiralty charts were from the eighteen hundreds.
__________________
Rick I
Toronto in summer, Bahamas in winter.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Quick reply to this message Share with Facebook
  #8  
Old 06-14-2010
sailingdog's Avatar
Telstar 28
 
Join Date: Mar 2006
Location: New England
Posts: 43,291
Thanks: 0
Thanked 11 Times in 11 Posts
Rep Power: 13
sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice
I'd have to agree with Vasco. The Explorer charts are very good and cover the Bahamas quite well.

I'd point out that in many areas, shoaling is a problem and that only recent local knowledge is really helpful. The Alligator River area is one that has a lot of shoaling and the charts are not dependable.
__________________
Sailingdog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
.

Still—DON'T READ THAT POST AGAIN.
Reply With Quote Quick reply to this message Share with Facebook
  #9  
Old 06-14-2010
Yorksailor's Avatar
Senior Member
 
Join Date: Oct 2009
Location: Pacific side of Panama
Posts: 497
Thanks: 16
Thanked 20 Times in 19 Posts
Rep Power: 6
Yorksailor is on a distinguished road
I agree on Explorer charts, I use them, but what legitimate governmental charting organization charted the Bahamas and produced comprehensive charts.

However, even though I use Explore Charts I would not trust them to do night entries...In the Bahamas it is 'Good visibility eyeball navigation' only

Last edited by Yorksailor; 06-14-2010 at 04:52 PM.
Reply With Quote Quick reply to this message Share with Facebook
  #10  
Old 06-14-2010
Vasco's Avatar
Warm Weather Sailor
 
Join Date: Sep 2006
Location: Toronto
Posts: 989
Thanks: 0
Thanked 6 Times in 6 Posts
Rep Power: 9
Vasco is on a distinguished road
Quote:
Originally Posted by Yorksailor View Post
I agree on Explorer charts, I use them, but what legitimate governmental charting organization charted the Bahamas and produced comprehensive charts?
More and more private enterprise is taking the place of government hydrographic services, especially in smaller countries that have few or no resources. That charts are produced by private companies does not make them any less "legitimate". The test is whether they are accurate or not. Some of the best charts in the Bahamas and the Caribbean are from private, non-governmental organizations. All the sailors in the Bahamas that I have met would far prefer the private Explorer Charts to those put out by the British Admiralty, a "legitimate governmental charting organization" as you put it.
__________________
Rick I
Toronto in summer, Bahamas in winter.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Quick reply to this message Share with Facebook
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
All About Charts Jim Sexton Learning to Sail Articles 0 11-28-2004 08:00 PM
All About Charts Jim Sexton Seamanship Articles 0 11-28-2004 08:00 PM
All About Charts Jim Sexton Her Sailnet Articles 0 11-28-2004 08:00 PM
GPS Gets More Accuracy Jim Sexton Gear and Maintenance Articles 0 05-21-2000 09:00 PM
GPS Gets More Accuracy Jim Sexton Cruising Articles 0 05-21-2000 09:00 PM


All times are GMT -4. The time now is 02:20 PM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.