NAUI Advanced Scuba Diver
76 Search and Recovery
you to know for other applications besides diving.
Two Half Hitches are useful for securing the end of
a line around itself for making a slipping loop. A Clove
Hitch is the same knot tied around some other object,
such as a post or bollard. A Bowline forms a non-slipping,
easy-to-untie loop in the end of a line. Because
a square knot may work loose if continually flexed by
wave action, a Sheet Bend is often preferable for joining
two lines together particularly if they are of different
diameters For most rigging purposes, these knots should
meet your needs. Remember that desirable features of
any knot are not only that it is easy to tie, but also that it
holds well and is easy to untie.
With the proper size lift bag rigged securely to the
object, you are ready to begin the lift. Signal your buddy
and make sure the area is clear of other divers. Use
the extra air source to put air into the lift bag. Proceed
slowly, adding a small amount of air at a time and noting
the effect. If you just keep adding air until an object
starts off the bottom, you will have more buoyancy than
is needed for the lift and it will be difficult to control. Try
to get the object neutrally buoyant so it hovers just off the
bottom. You can then check the rigging to make sure it
is holding properly when it is supporting the full weight
of the object. Start the lift on its way when you are ready
by simply pushing the object upward a little. The expansion
of air from the pressure reduction will be enough
to establish positive buoyancy. It is important that you
and other divers stay clear of the area below a lift. You
and your partner should ascend with the lift and use the
dump valve in the lift bag to maintain a proper ascent
rate. If the lift gets out of control by rising faster than
it should, let it go, swim horizontally away from it, and
surface. It is possible that the bag may clear the water
enough to dump air when it reaches the surface, and
the object will immediately sink. You do not want to be
underneath if this happens. In the event that you vent too
much air and the lift begins to sink, release it, follow it to
the bottom, add air and start again. Do not try to support
a sinking lift by holding it and swimming or by trying to
add air to it as it descends.
OVERVIEW OF A TYPICAL SEARCH AND
FIGURE 7-8. knots