There are a
variety of search techniques that are applicable to the underwater
environment. While in theory, some patterns based on land or air
search patterns should work. . . . in practice they prove to be
inadequate underwater due to such factors as limited visibility,
chaotic bottom contour, and submerged hazards. Experience has shown
that to be efficient underwater a search pattern must be simple. The
simpler - the better.
search techniques rely on one common element: the adoption and
execution of a defined search pattern. The pattern must commence at a
known point, cover a known area, and terminate at a known end point. A
search is conducted by employing search sweeps that slightly overlap.
The last known position of the object of the search is used as a
patterns lend themselves better to a particular type of search than
others, depending on the type of bottom, depth, visibility, number of
divers, size of the missing object, and how the base of operation is
set up. Ten search techniques (patterns) are listed below. There may
be others that are more practical to use under ice, in rivers, or in
dams where the bottom is filled with trees or other growth; however,
an imaginative combination of two or three of these patterns will
prove effective in almost any instance.
THE CIRCULAR SEARCH PATTERN
THE SEMI-CIRCULAR SEARCH PATTERN
THE STRAIGHT SWEEP SEARCH PATTERN
THE GRID OR CHECKERBOARD SEARCH PATTERN
THE STRAIGHT SWEEP IN CURRENT
THE STRAIGHT SWEEP ALONG A
SEARCH WITH A WEIGHTED LINE
THE PLANING BOARD IN SEARCH
TOWING DIVERS BEHIND A BOAT
THE COMPASS SEARCH
THE JACK-STAY OR "Z"
critical, regardless of the type of search pattern selected that each
diver participating in the search be able to guarantee one of two
1. The object is in
his assigned search area (assuming only one object is being
searched for, only one diver will be able to say this).
2. The object being
searched for is positively not in his assigned search area.
Divers participating in
a search must keep in mind that the search can be greatly complicated
by stirring up the bottom. Everything possible should be done to
keep from disturbing the bottom and stirring up silt, sand, etc.
This is normally done by maintaining slightly positive buoyancy, a
head down feet up orientation and arching your back as you kick.
Divers should refrain from: wading about in water adjacent to the
search area; treading water in a vertical position when near the
bottom; touching the bottom with hands, fins, or body anymore than
is absolutely necessary; entering and exiting the water in the
vicinity of the immediate search area; or deploying weights and
anchors by dropping them from the surface.
The circular search pattern can involve any number of divers, yet it is
effective for single diver. The first item of importance in using this
pattern is to make sure that the anchor used as the base of theascending/descending
line is of the correct shape and weight to remain fixed during the search.
Next, be sure to mark the starting point of the circle so that you will
know when you have completed 360 degrees.
A line is
secured to the anchor and one or more divers are spaced along a bottom
(search) line according to the visibility of the water. When a 360 degree
sweep has been completed, the diver furthest from the anchor remains in
position, otherwise the size of the first circle will not be known and a
small object might be missed as a result of the larger second sweep. The
number of circles made from one reference point is dictated only by the
length of the line. It is the responsibility of the outside diver on the
line to keep the line taught, consequently his/her area of search is less
than the others. Thus, you have another reason for this diver not moving
at the end of the completion sweep.
If the object is
not found from the first point of reference, the location of the first
anchor and the distance of the first search is marked with surface buoys.
The anchor can then be moved to a new location and the search repeated.
We utilize a flat 25-pound
weight (brake drum), attach a 2- to 3-foot length of chain to
it with a swivel at both ends. The chain will extend above silt and give
the diver something to snap his or her search line into, the swivel
allows it to rotate to prevent fouling. The ascending/descending line is
then attached to the top swivel and goes to the float (mini-mother)
at the surface and excess line (scope) is allowed to suspend itself with
a 5-pound counter weight below the surface. The mast on the mini-mother
is used for ranging and positioning from the beach. Two shives at least 12
inches apart (or a spreader system) are used to keep the
ascending/descending line from fouling with the counter weight. In zero
visibility searches the diver uses the
to snap into the chain. The
is used with better visibility - in either case a
marker is utilized to mark starting and ending points and
expansions are done by coming inside the already searched area and
letting out appropriate line or rings and then moving out to the new
perimeter with marker and repeating the pattern.
SWEEP SEARCH PATTERN
A straight sweep
from a single guide line is generally used when there are many divers
participating and there is a fair amount of visibility.
should be placed sufficiently beyond a point where the lost object is
thought to be. The guide line is made taut from the anchor to a point on
the shore, and a second line along which the divers swim, runs at a right
angle to the guide line. This line is then tied to the guide line with a
The divers swim
out to the anchor. Then the diver closest to the anchor holds his/her
position while the others swim a 180 degree arc so that they are headed
back toward shore. They determine that they are in line by prearranged
signals that can be given down the rope which they are holding. When they
are in a straight line they swim back to the shore. In this manner ten
divers (assuming 10 foot visibility) can, in one sweep, cover a two
hundred foot area in one sweep.
In practice this
is a very difficult feat. One problem is that the anchor deployed in the
water must be very heavy as this deployment is important to keep the line
taut. A second problem is that it is extremely difficult to keep very many
people abreast in the water without utilizing something rigid like a pole.
A rope doesn't get it. (We don't swim at the same rate, nor equalize
easily all the time, and there are too many things to go wrong).
THE GRID OR CHECKERBOARD
The grid or
checkerboard search pattern requires four anchors and four floats. Guide
lines beneath the surface may be used. The divers may swim the guide lines
or, if none, may use a compass to swim back and forth within the area
marked off by the buoys.
In this pattern,
as in others, it is possible to control the divers by a signal from the
surface. If there are no obstructions on the bottom the divers may use a
line between them to maintain their position as the pattern is swum. When
they reach one edge of the pattern a man on the surface with a line to one
of the divers signals him of this fact. A jerk on the line alerts the
other divers who then make another sweep according to their prearranged
obstructions or kelp prevents the use of a line between divers, signals
from the man on the surface can be sent to the divers by pounding on a
hollow pipe which is partially submerged in the water. The divers in this
situation swim the pattern by compass. This is an especially useful
technique when searching in deep water.
If the search is
expected to be fairly extensive, enough pattern is laid out to last the
length of one tank of air.
STRAIGHT SWEEP IN CURRENT
where there is a current in one direction, the straight sweep is used. The
anchor is secured to a fixed location, and rope is played out from shore a
given distance each time the divers (one or two only in this pattern) swim
out to the anchor and back. Consider starting the search in a current
downstream in order to avoid divers stirring up the search area thereby
STRAIGHT SWEEP ALONG A SHORE LINE
method for searching a quiet body of water, such as a lake or pond, is to
have divers spaced along a guide line as visibility will permit. The guide
line is then held by someone on shore who walks along with the swimmers as
they search. If the object is not found, the last diver holds position
while the others take a position further out on the guide line, and
another sweep is made.
This type search
is effective when searching for small children who may have drowned, as
they will generally be close to the shore.
SEARCH WITH WEIGHTED LINE
When a search is
required around a pier that is oddly shaped or one that has pilings to
provide boat slips, divers may swim from a guide line which is held by a
person on the pier.
heavily weighted line to the surface as a reference point, divers may take
positions along a bottom line. It is important that they swim slowly so
they do not get ahead of the guide line and swim under the pier.
weights will keep the line taut while the person walks around the edge of
PLANING BOARD IN SEARCH
If a large area
is to be searched and the object being sought is a large one, it is
possible to use a planing board (sea sled) behind a boat. The planing board enables the
diver to stay near the bottom, but the diver must always be conscious of
the fact rapid ascents might result in serious problems.
When using this
technique a marking device should be carried by the diver. When the object
of the search is sighted, the diver merely drops from the board and swims
to the object. A small line is then tied to the object and the marker is
sent to the surface. The marker assures finding the object again and
should keep the diver from being struck by the boat, which should stay a
safe distance from the marker until the diver surfaces.
TOWING DIVERS BEHIND A BOAT
In the ocean where there is
unlimited visibility, or in rivers where it is possible to see the bottom,
divers may be pulled behind a boat without the aid of a planing board.
The number of divers towed depends on the current of the water and speed
of the boat. The best method is to have a rope for each diver being
The same marking technique is
used in this search as was used in the one before on the planing boards.
At times, conditions are such
that it is not feasible to use search lines. When such is the case a
search can be conducted using an underwater compass. Visibility
permitting, the use of the underwater vehicle (e.g.,
DPV, Scooter, etc.)
provides an efficient method of searching an area by use of the compass.
The underwater vehicle not only allows the diver to search a given area
faster, but also greatly increases bottom time by reducing expended
effort and thus air consumption.
THE JACK-STAY OR "Z" PATTERN
jack-stay pattern, sometimes referred to as a "Z" pattern can be
utilized when searching a given area involving a steep embankment. The
advantage of this search method in these circumstances is that a diver
(or divers) can conduct the search from deeper depths to shallower
depths. (The use of the circular pattern requires a diver to
constantly change depths when conducted on an embankment.) The
disadvantage of this search method is that it is slow to employ and
jack-stay rig consists of two down lines with small floats (area
marker floats). Attached to each down line is a 15-20 pound anchor. A
length of line 50-75 foot long is attached at each end to the two
anchors. Longer lines tend to be hard to control and do not work as
well. An advantage of the down lines and surface floats is that
surface personnel can readily track the progress of the search.
One diver or
two divers maximum, swims along the line from anchor to anchor. Upon
reaching the opposite anchor, the diver pulls the line taught and
moves the anchor in a predetermined direction a distance which is
dependent upon the visibility and the size of the object of the
search. The diver then reverses direction somewhat overlapping his
previous pattern and repeats the sequence.
A diver (or
divers) terminating a search simply ascends on one of the down lines.
Should it be necessary to continue this pattern, another diver can
descend the same down line and pick up where the first diver left off.
For more search patterns, see
Basic Search and Recovery
from the National Association of Resuce Divers.
Photos courtesy of