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From: (no name) (no email)
Date: Thu Nov 04 2004 - 12:13:40 EST
Quoting Wally <>:
> Instead of flames, how about an intelligent discussion
> of the merits of paper charts vs electronic...up here
> in Georgian Bay, where we have lots of granite instead
> of sand, every single boat I can recall this season
> that came in with a hole in the bottom, or damaged
> keels, outdrives, props...was running with electronic
> charts. Not some - all of them.
> Why?
REPLY
Wally, you have hit on one of my favourite topics.
I cruised Georgian Bay from 1969 to 1999. planned a number of squadron
navigation exercises involving dozens of newbie boat owners and have written
extensively on e-charts in several magazines.
In addition I have participated in hydrographic survey work in Georgian Bay.
Lastly I also worked as an installer of electronic navigation equipment so I
can relate numerous stories of how these systems were used and sometimes abused
by my customers.
The difference between e-charts and paper charts lies in how you do the
plotting. With paper charts you are forced to look up and around you to take
compass bearings etc. This mean you actually have an awareness of what is
around you. Not just vessel traffic but also nearby land and nav aids marking
under water hazards.
By contrast e-charts automatically plots your vessel position on the screen.
Thanks to zoom-in and other nifty software features this allows the operator to
focus more closely on the display screen. Unfortunately this also means he/she
does not necessarily lift their eyes to look out the windscreen or over the
dodger.
A second problem has to do with how the e-chart systems work. The vessel icon
is not scalable to match the actual vessel outline. Only the center point of
the icon represents a true depiction of whrer the GPS antenna is located.
When you zoom in the vessel icon remains the same size.
On real ECDIS systems the display would have the true scale of the chart and
the vessel shown.
This means you get a better idea of just how close the hazard or shore is to
your vessel.
When zoomed in fully it is deceptive as to how much clearance you have between
your vessel and the hazard.
Most people use raster charts. For Georgian Bay this typically measns a chart
scale of 1:20,000 or 1:40,000 Such a scale cannot precisely or accurately
depict the finer details of rocks etc. The chart will show a rock symbol or a
shoal patch. Within the limitations of the paper chart it is accurate.
However when this is displayed on a computer screeen and zoomed in the true
proportion and relationship is lost.
I know of one boater who tried to run up little dog channel using his
electronic chart system. He was very surprised to fel a thump as his boat hit
the rocks lining the shore. Only then did he lift his eyes and look out on the
real world. Duh!!!!
For anyone not knowing the area Little Dog channel is about 15 feet wide and
has maybe 6 feet of water at the most. The shorelines are unforgiving granite
and the channel is not straight.
Another factor which comes into play is the lower water levels experienced in
Georgian Bay for the past few years. Many of the charts of the area are
several decades old. People have become accustomed to sailing in deeper water
and not having a problem. Suddenly the water drops by several feet and now the
rocks which were safely under the keel jut up and snag the boat.
I'm not saying the boaters are blameless but when you cruise an area for years
you develop a feel for "local" knowledge and sometimes you forget that Great
Lakes water levels do change. Coast sailors are more familiar with daily tide
changes so they are less likely to forget.
So even if the GPS system is accurate, and you do use up to date e-charts it is
easy to run afoul of rocks in Georgian Bay.
I have now seenin most popular boating places around the North American
continent. I will say that Georgian Bay presents one of the most chanllenging
navigational tasks of any place, bar none.
The high incidence of holed boats is not just a reflection of the relative
merits of paper versus electronic charts. It reflects how people perform the
task of navigating their boats and also how non critical they see the task.
Most boaters do not practice precision navigation. They consider it too much
bother. They are out there having fun. So they do not take it as seriously.
Georgian Bay almost demand that you have two people involved. One person steers
the vessel and one person does the navigation, full time.
Anmything less is an invitation to running aground.
Cheers
Arild
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