GPS chart discrepancy article

[Roger Long]

The issue of "Points East" just now hitting the stands has an article about the significant chart discrepancy discovered at or near the spot where the Portland, Maine fireboat ran aground. If you aren't in New England or want to read it on line, it's now available at

http://www.pointseast.com

If you want to see the charts, you'll have to read the full version of the issue available in the link at the bottom of the page instead of the feature story version.

I've had some interesting email exchanges on this with the owner of a navigation software equipment company who is on an industry/government charting standards advisory group and the fellow who wrote the article sidebar. I just got an email from a product manager at West Marine is found it very interesting and said is going to talk to their GPS suppliers.

There is going to be more discussion about this soon on the "Points East" forum:

http://www.pointseast.com/forum/index.php

 

[All U Get]

Hi Roger,
Good work on finding that problem. I venture through there quite regularly but must be too shallow to rub the bottom. Seen the Islander, I think, in there also. Did the daymark get moved? Maybe that's what I overheard a few years back.
All U Get

 

[Tim R.]

Roger, your diver undoubtedly saw some lead from my Pearson 28 from about 7 years ago. This is a fairly well known ledge(at least the folks I know). I have instructed many boaters over the years to keep well clear of that day marker. Great article though.

I am very surprised that the CG did not know about it.

 

[Roger Long]

your diver

Not my diver

 

[shemandr]

That does scare me about Maine. We do have rocks here but usually groundings are in shoaling sand and result in little damage.

 

[Ross]

One of the problems with charts is called scale. A 1:40,000 chart will represent a pencil line at 70 feet wide. the coast of Maine was carved by glaciers and there are erratics and narrow ledges that could be missed by hand line soundings. One of the "Queens" hit an uncharted ledge of Rhode Island a few years ago.
There is an effort by several groups to use the integrated depthsounder,gps and computer to plot continous bottom terrain. This will help in areas where the Datum is from 1928.

 

[sailingdog]

Of course, the more heavily travelled an area is, the more likely all the hazards in the area are to be charted.