CAUTION AROUND
OUTLYING REEFS
Charts produced by foreign agen-
cies often use smaller scales for close
coastal navigation. For example, many
Bahamas charts lack detail for ap-
proaches to islands or off-lying reefs
because their scales are much smaller
than 1:80,000. Distances between
soundings are sometimes hundreds
or even thousands of yards. Some areas
show no depths at all! When in doubt,
use well-traveled routes or seek local
knowledge.Box-Plot Your Position
If you stand back and look at any chart,
you’ll notice a system of grid lines
overlaying the land and water areas.
These grid boxes form the basis for
navigation. The top and bottom of each
box is a line of latitude, or a parallel.
The right and left sides of each box are
lines of longitude, or meridians. When
you box-plot, you use sides of the box
to help pinpoint your boat’s position
inside the box. This makes a fast and
accurate way to transfer your position
from your GPS to your chart.Skipper Tip—24-Hour Time
Navigators throughout the world
use the 24-hour clock to avoid
confusion (as do colleges and
universities). Remember these two
things: 0000 is midnight and 1200
is noon. From midnight until 1200,
you add the number of hours past
midnight. For instance, 1 hour past
midnight is 0100 (1 am), 2 hours
past is 0200 (2 am) and so forth
until 1200. From 1200 to midnight,
add 1 hour to 1200. For instance,
1 hour past 1200 is 1300 (1 pm),
2 hours past 1200 is 1400 (2 pm).
Practice until this becomes second
nature. Use only 24-hour time for all
chartwork, log entries, and talking
on the marine radio.
24-HOUR TIME CLOCK TIME
0000 = MIDNIGHT
0100 = 1:00 AM
0200 = 2:00 AM
0300 = 3:00 AM
0400 = 4:00 AM
0500 = 5:00 AM
0600 = 6:00 AM
0700 = 7:00 AM
0800 = 8:00 AM
0900 = 9:00 AM
1000 = 10:00 AM
1100 = 11:00 AM
1200 = 12:00 PM
1300 = 1:00 PM
1400 = 2:00 PM
1500 = 3:00 PM
1600 = 4:00 PM
1700 = 5:00 PM
1800 = 6:00 PM
1900 = 7:00 PM
2000 = 8:00 PM
2100 = 9:00 PM
2200 = 10:00 PM
2300 = 11:00 PM
Supplies and Tools
Needed to Box-Plot
Your Position
X pencil
X artist’s or draftsman eraser
X straightedge
X plotting compass