03/24/2002

SILICON SEA CHARTLETTS

These are minimal charts with not much more than a coast outline and
a lat-long grid.  They are all were derived from the old Map Viewer program at 
PARC, with place names from assorted atlases and encyclopedias.  I don't have
any access to the detailed information usually found in navigation charts and
these might better be called "chartlettes".  They are still usefull for
providing some geographic orientation for the Silicon Sea cruise and if printed
can be used as plotting sheets.

These chartletts are of sufficient accuracy to use as plotting sheets for the
Silicon Sea navigation problems they supplement.

For plotting you will need a course plotter or some device for measuring 
angles.  Each chart has part of the latitude scale graduated for measuring 
distance.  You need to construct a scale for measuring longitude but this 
is easy to do using the method outlined in Bowditch in the emergency 
navigation section.  You can probably get an accuracy of about 2 nautical
miles.

Chartlets with a .GIF suffix are plotting charts based on posplot.exe. After
Leg 89 the chartletts are .jpg. The .jpg chartletts(plotting sheets) are hacked
together using Navigatio 4.1, scanning them, and converting using Paint Shop Pro 7.0.


TO MAKE YOUR OWN PLOTTING SHEETS

    1) A pencil and ERASER.
    2) Something to draw straight lines with.
    3) Something to layout angles with.
    4) Something to use as a plotting sheet.
    

NAV PLOTTING

Below is Dan Hogan's QED plotting for the financially under-privileged.
Blatantly stolen from Self Contained Celestial Navigation with H.O. 208,
John S. Letcher, 1977, International Marine, ISBN 0-87742-082-3.

Use lined paper, college ruled, Turn the paper 90d, so the lines are
vertical. Ruled lines are used for longitude. Every sixth or twelfth lie is
darkened to represent a whole degree of longitude. (depending on the scale
desired).

Lines of latitude are added by construction starting with the lowest
latitude desired. Whole degrees are 60 miles. From your lowest Latitude line
at the most R/H longitude line, draw a line at an angle up from the
Latitude of your lowest latitude line plus 0.5d(ie.: 28.5d). For ten miles
to the vertical line use 6 lines; for 5 miles to the line use 12 vertical
lines. Where the angled line crosses your 6th or 12th line swing an arc
until it touches your R/H vertical longitude line. This is the point of the
next latitude line. Draw a line perpendicular to the longitude across the
page. Repeat the process with each higher latitude (29.5d), etc.

The bottom angle line, where it crosses the intermediate vertical
longitude lines, is the distance interval. 10 miles each line for 6 line
spacing. 5 miles each line for 12 line spacing. This forms a handy scale of
miles or minutes of latitude. The accuracy is within the tolerance of your
#2 pencil point.

     
Dan Hogan WA6PBY		     
West Covina, CA		     
dhhogan1@earthlink.net
C27 - GACHA
San Pedro, CA
