I was thinking about the convenience of a combination GPS and chart
display now that the prices have dropped below one BU, but the cost of
solid state charts still discourages me. Before depleting my bank
account, I decided to try a makeshift unit using equipment I already
have. In my computer junk drawer I have an older Macintosh 1400
portable, an ultra reliable laptop that has long been superseded by the
iBooks and Powerbooks. The Mac 1400 has a good display and is nice and
compact, although a bit heavy. It has two PCMCIA ports. It will run on
the 12 v. DC from the cigarette lighter outlet.

As some of you know, I run GPSy as a navigation program because it
permits the use of self scanned charts. Fugawi will do the same for PCs.
Each chart is initialized for navigation by identifying the coordinates
of three points. I have many of these charts of my usual cruising areas
scanned from NOAA paper charts and burned on CDs. The charts are kept as
JPG files using a moderate amount of compression. Typically an 11x14"
section of a standard NOAA chart generates a 2 MB file when scanned at
300 dpi. Last week I transferred several dozen chart files and a copy of
GPSy 3.9 software to a 512 MB Compact Flash memory and slipped it into
one computer slot using a PCMCIA adapter. The other slot was filled with
a PC card GPS.

When I turned the unit on and loaded the GPSy program, it recognized the
GPS. The charts could be loaded from the Compact Flash memory as if they
were on disc. My boat is still in shrink wrap pending a launch date at
the end of the month but I did put the computer in my car and it plotted
my course on a brief run along the shore.

Why bother? Compact Flash memories now cost about $50 in 512 MB capacity
and are available in up to 2 GB capacity. I can load all of the NOAA
charts for the entire country on one of the larger memories. The 512 MB
chip will hold all my charts for the ICW from Maine to Florida with
space left over. It would take 5 wide area C-Map chips to cover the same
area at a cost of nearly $1000. A prudent mariner would need paper
charts for backup anyway so why not put copies of the charts in the
computer.

I'll let everyone know how this experiment works out at the end of the
summer.

Now before anyone berates me for being foolhardy enough to trust my life
and that of my crew to a cobbled up kludge of a navigation system, I
suggest you read Nigel Calder's critique of the accuracy of electronic
charts (and paper charts too) in the current May/June issue of Ocean
Navigator. Calder bemoans the fact that the level of survey accuracy of
most 1/20,000 scale inshore charts is typically 30 meters, while the
accuracy of GPS position location is about 3 meters. And, of course,
many charts are based on surveys done 100 years ago. Calder concludes
that any navigator using electronic plotting should place an imaginary
circle of possible error around the boat's plotted position. The circle
of error represents the extent to which the chart features around the
boat may be out of place. ALL potential hazards should be kept out of
the circumference of this circle. Vector charts are no better than
raster charts in this regard since most vector charts are simply
digitization of the underlying raster chart and carry all its errors. In
this regard, my own system is probably no worse than a purchased custom
chart plotter. Or as Bill Clinton might say "It's the charts, Stupid."

With data errors up to 30 meters, electronic charting should not be used
as the primary means of guidance in many inshore situations. I would
not, for example, enter Branford Harbor in the fog or navigate through
the Thimble Islands, using electronic charting. Nor would I rely solely
on electronic charting in the narrower confines of the ICW. I have,
however, been a guest on several boats in just those situations where
the owner regarded the magenta line as gospel and steered the boat
looking at the display instead of out the windscreen. On such trips I
always make careful note of the location of all lifejackets.

The greater the degree of precision with which a boat's position can be
plotted, the more important it is to maintain a degree of healthy
skepticism of the accuracy of electronic charts. From my point of view,
whenever a charted hazard comes close to the circle of possible error
around my boat, roughly estimated as the size of a football field, I
rely on eyeball navigation.

Larry Z

If total cost saving is the goal, and you scan your own charts like Larry
describes, then look at http://www.sping.com/seaclear/, free chartplotter
software with some nice features, and also with software to identify
co-ordinates of scanned charts. Used to be NOAA had 'not for navigation'
raster scans of all charts available for download, which worked well with
this, but I can't find them anymore.

Tim Holock
Annapolis

<<I was thinking about the convenience of a combination GPS and chart
display now that the prices have dropped below one BU, but the cost of solid
state charts still discourages me. Before depleting my bank account, I
decided to try a makeshift unit using equipment I already have. In my
computer junk drawer I have an older Macintosh 1400 portable, an ultra
reliable laptop that has long been superseded by the iBooks and Powerbooks.
The Mac 1400 has a good display and is nice and compact, although a bit
heavy. It has two PCMCIA ports. It will run on the 12 v. DC from the
cigarette lighter outlet.>>