NAUI Advanced Scuba Diver
30 Navigation
read directly under the lubber line. A needle compass is
similar, except that you rotate the bezel to align 0° with
the north end of the needle. Your bearing is read at the
lubber line.
An indirect reading compass has fixed markings of
0° to 359° in a counterclockwise direction around the
edge of the compass body. The degree markings do not
rotate, and 0° is permanently aligned with the lubber
line. When you take a bearing, the compass needle or
the compass card points to the bearing in degrees. The
reading is “indirect” because 0° is always in the direction
of travel, and the compass needle points to the bearing.
With an indirect reading compass, the bezel index marks
are used to register the relative position of the needle so
that you can easily realign the compass later in the dive
(figure 3-3).
A side reading compass is preferred by many divers
for its ease of use (figure 3-4). In a side reading compass,
the compass card has a skirt around its edge that
is marked 0° to 359° in a counterclockwise direction. A
window in the side of the compass body is in line with
the lubber line and displays the degree readings on the
skirt to the user. To obtain a bearing you look across the
compass and through the window. Your bearing is shown
in the window, and you need only remember the bearing
or note it on your slate for later reference.
Each of the three types of compass has its devotees,
and you will probably encounter all three in your diving
career. If you find one type easier to use, you should look
for it when you acquire your own compass.
MEASURING DISTANCES UNDERWATER
To navigate effectively, you need to be able to estimate
the distance you have traveled. If your dive site is a
hundred yards or a hundred meters offshore, you should
know when you have traveled that distance. When following
a general course, maintaining correct headings
is one requirement, and estimating the distance for each
leg of the course is another. One of the sinking feelings
in diving, is swimming a course and wondering as you
approach the end, “My heading must be wrong. I ‘know’ I
150°
Indirect Compass
150°
Needle-Direct Compass
150°
Card-Direct Compass
FIGURE 3-3. direct and indirect reading compasses