Chapter 3- Navigation
Navigation
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FIGURE 3-4. A side reading compass has the additional benefit of letting you check your heading at a glance, without taking your eyes off of your
must have passed it.” For some situations such as searching,
distances must be measured accurately. For general
diving, approximations of distance will usually suffice.
Several methods may be used to estimate distance. Let’s
look at some.
Most of us do not carry a long tape measure in our
BC pocket. Even if we did, deploying and retrieving it
would take a lot of time away from the enjoyment of our
dive. What other, easier measuring methods do we have
available?
Probably the most accurate way to estimate distance
is arm spans. For most people the distance between the
fingertips of their outstretched arms is about equal to
their height. If you are 180 cm (5 ft 11 in) tall, then this
is about the distance you can reach. A quick, but good
estimate of short distances can be made by stretching
your arms out alternately from touch-down point to
touch-down point as you swim.
The most common way to estimate distance is by
counting kick cycles. This is similar to counting your
paces on land. To use this method, you have to establish
the length of your personal kick cycle by swimming
a measured distance as you count kicks. (A measured
distance is easy to establish in a swimming pool. If you
are in an open water setting you could use a measured
length of line, say 30 meters (100 feet), and anchor it
to the bottom.) One kick cycle is counted each time the
same leg comes down as you swim. When measuring your
kick cycle, do not try to rush or use an exaggerated kick;
use a kick that you can easily repeat just as you do when
measuring by paces on land. Divide the distance swum by
the number of kicks to find your distance per kick cycle.
Since measuring by kick cycles is an estimate, you might
want to round this number to something that you can
easily remember and use in your head. If your calculation
is 94 cm (37 in) per kick, 1 meter (3 ft) per kick is probably
close enough. Establishing the length of your kick
cycles is likely to be an exercise you will perform in your
Advanced Scuba Diver course.
Another way to estimate distance is the time it takes
to swim the distance. This works if you are swimming
directly to your goal. But most of us like to take time out
to examine interesting sites, aquatic life, and objects; so
timed swimming tends to lose accuracy.
The same can be said about using air consumed
(psi or bar used) to measure distance. To use the air
consumption method to measure distance, you must
resolutely proceed toward your destination and not
target.