Chapter 4- Night and Limited Visibility Diving
Night and Limited Visibility Diving
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reefs are just offshore from a smooth, unobstructed entry.
Diving in familiar areas is recommended. Even then, it is
a good idea to dive the known area the same day prior to
a night dive to evaluate the conditions and to reacquaint
yourself with the site. No matter where the dive is based,
it is helpful and advisable to have someone remain above
water during night diving activities as a contingency
against mishap.
The planning process for a night dive is even more
important than for regular dives. Because of the heightened
excitement from anticipating a night dive and the
added challenge of working in the dark you should be
sure to give extra attention to all aspects of your dive
plan. Make sure your dive lights have fresh batteries or a
full charge.
As you prepare to dive, be sure to review signals
with your buddy. Standard hand signals can be used, but
remember that they must be given in front of a light in
order to be visible to others. Signaling with your dive light
is unique to night diving. A large “O” formed by moving
the light in a slow circle is the long distance version of
the “OK” signal. Rapid wiggling of the light from side to
side is often used to signal, “Attention” or “Look here.”
Distress is signaled by extending the light out to one side
and moving the light rapidly in long, exaggerated 180
degree arcs overhead. These light signals are useful both
at the surface and underwater.
Be sure to note some distinctive feature on your
buddy like the color of his or her mask, so you can easily
recognize him or her underwater at night. It is not
uncommon for dive teams encountering one another to
accidentally switch partners during a dive or even return
to a different boat!
Other preplanning items are the same whether day
or night diving is being conducted. Discuss and agree on
the general course to be followed to improve buddy coordination.
Agree in advance which buddy will navigate for
the first half of the dive as the partner points out things
of interest. The roles can then be reversed on a reciprocal
course during the second half of the dive. Before
you attempt a night dive, you and your buddy should be
practiced at successfully staying together during daytime
dives.
As stated earlier, lights should be set up to help you
identify the exit point prior to your dive. When using
shore lights that are already in place, only lights that are
fixed and can be relied upon to remain on until after
diving operations end should be used. For example, street
lamps are usually reliable, but a residential porch light
might be switched off. If you have set up your own pair of
lights as a range, consider it another good reason to have
someone remain on shore to ensure the lights are still in
place at the end of the dive.
Before you enter the water to begin your night dive,
double check to be sure your light is attached to your
wrist by a stretchable lanyard. This will prevent it from
being dropped after your entry and while you make
last minute preparations at the surface. Experienced
night divers facing a long swim usually want to leave
their lights off until they reach the dive site. This will
help avoid having the light flashing about on the surface
and from depleting your batteries prior to the dive. Dive
preparations also include checking your gear for proper
adjustment, and setting a compass heading for reference.
Whenever possible descents should be made on a
line or on a gradually sloping shore. With no external
references at night, it is easy to become disoriented. The
disorientation can range from not knowing which way is
up, to extreme dizziness and must obviously be avoided.
The line serves as a reference and prevents the problem.
FIGURE 4-8. Maintaining neutral buoyancy will allow you to avoid
landing on the bottom in the wrong place.