Originally Posted by MarkJ
My thoughts are the prudent navigator should NOT be using paper charts at all.
They are a historical thing used in the past. They are neither updated, nor correct. They are stupidly slow to use even by an expert navigator compared to electronic charts and a chart plotter.
I think they will be illegal within a few years in any area that has modern electronic charting.
If someone ran over my boat killing crew and said they were using paper charts I would sue their butt off.
Very sorry to say it, but this is either a spoof or one of the most ill-considered commentaries in a whole thread full of inaccuracies and technical omissions. More emotion here than careful thought, based on knowledge, skills, and experience.
One hardly knows were to begin.
Paper Charts, and Electronic Charts (Raster and Vector)
In almost 40 posts, no one has bothered to differentiate between raster
electronic charts and vector
electronic charts. The former are EXACT replicas of paper charts -- they're just snapshots of the real paper charts, and are available free of charge from NOAA. They are regularly updated by NOAA.
The latter, vector charts
, are a different thing altogether. These are what is found on chartplotters and are compiled by different entities. While there are some advantages to vector charts (smaller file size, overlay control, etc.), there are also some significant drawbacks. And, you cannot assume that they have the same accuracy as paper charts or their snapshot electronic charts, the raster charts. Some do, some don't. Vector charts must be digitized, and the quality of digitization varies considerably. Vector charts often do not contain much of the shore-based information contained in paper or raster charts. Even those from a single
source, e.g., NOAA can differ. NOAA actually maintains two libraries of electronic charts: raster and vector, and strives mightily to ensure that each is as accurate as can be. Not all providers are as diligent.
The term "GPS charts" has been used several times in this thread. There is no such thing. Chartmakers use a number of georeferencing aids, including GPS, where possible. But funds needed for up-to-date surveys are very limited and, as has been noted, some areas haven't been surveyed in many years.
By default, most GPS units use WGS-84 for their base datum. Many include the option to choose other datums, where needed. Charts all have to be referenced to some underlying datum. These days, almost all charts in the U.S. use WGS-84 also.
Not understanding this business of datums can lead to grief, especially outside the U.S. I once witnessed the loss of a 70' custom sloop
in the British Virgin Islands
due to the failure of it's professional crew to pay attention to the difference between the GPS datum they were using and the datum of the chart they were using at the time.
Accuracy of Plotted Features on a Chart
Even assuming that the paper (or raster) chart is based on the same datum as the GPS in use -- say WGS84 -- you can't be absolutely sure that the GPS-plotted position on the chart corresponds to reality. There are lots of errors in charts used worldwide, some small, but some involving large differences beween plotted position and actual position. Many sailors in Baja
have found wide discrepancies, as have sailors in the Windward Islands
and in the Pacific.
That said, I've found U.S. raster charts and paper charts to be extremely accurate.
The plotted buoys, channel markers, etc. on any chart -- paper, raster or vector -- may be innacurate due to incorrect geolocation or, more likely, to the aid having been moved intentionally or not.
Additionally, there may be new nav aids and/or obstructions which are not shown on the chart -- paper or electronic. No matter how often they are "updated", it's impossible to keep up with all changes.
All These Innacuracies -- What to Do?
The prudent navigator will use everything available to ensure safe passage
. This includes the Mark I eyeball -- the most important nav aid there is -- assisted by charts, compass
, fathometer, GPS, radar
, and other means as indicated. He/she will NOT rely 100% on electronic means, or on any other single source. To do so is the mark of an inexperienced and foolish navigator.
In the past few years there have been numerous tragic wrecks involving loss of vessel and loss of life due to incredibly stupid navigational errors. Two sailing vessels have actually run up on the north seawall at the entrance to Charleston, SC. This long seawall is well marked, and the Charleston shipping
channel is wide and well buoyed. Furthermore, it is deep
, and anyone paying attention to the fathometer would know they'd strayed from the channel long before it would be possible to hit the seawall.
I apologize for the long post, and hope I haven't offended anyone. But navigation is a serious matter and there's an awful lot of bum information out there.