JRC JMA-9932-SA User Manual

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Relative vector
CPA RING
Fi9.1.20
Collision
Triangle
Relative
Vgctorand
True
Vgctor"'
I
"
r t
! I
t
"
I'
t r
"'
I t
Form
two
points
of
view,
collision
prediction
and
avoidance,
it is
necessary
to
obtain the
relative
vector
of
other ship for
prediction
and
the
true
veclor
of
other ship
for
collision
avoidance
in order
to
grasp
other
ship's aspect.
The relationship
between
the relative
vector
and
true
vector
is shown
in
Fig.1 .21
.
Both
rough
CPA
and TCPA can
be
obtained
easily
from
the
relative
speed
vector of
other
ship. This
method has an
advantage that
the risks
of
collision with
all
other ship
can
easily be
obtained
from
its
true
speed
vector,
enabling
other
ship's
aspect to be
seen
at
a
glance. Thus, the aspects of
other ships
(transverse,
out sail,
parallel
run,
reverse
run, etc.)
as
described
in the Act of Prevention
of Collision
at Sea
can be readily
grasped.
lf there
is
a
risk of
collision
with
other
ship, the
operator can
determine
which
rule
to be applied
and how
to operate
own ship.
Basic Goncept
of
Collision
Avoidancg" "
r'' r
"'
r r r''
There
are
two
aspects in
collision
avoidance: collision
prediction
and avoidance.
Collision
prediction
is
to
predict
that two or
more vessels
will
happen
io occupy
the
same
point
at the
same time,
while collision
avoidance is
to maneuver
vessels not to
occupy
the
same
point
at the same
time.
In
practical
operation
of
vessels, a spot
of collision
has to
be deemed to be a single
point
but
a
closed
zone. The closed
zone
is
conceptually
defined
as CPA
(Closest
Point
of
Approach). ln
collision
prediction,
the time to be
taken
until
a ship reaches
the
CPA
is
defined
as a TCPA
(Time
of CPA).
Fig.1.20
shows a
diagram
called
"Collision
Triangle".
CPA
/-"'
TCPA
(Time
of CPA)
1-28

JRC JMA-9932-SA Specifications

General

Brand	JRC
Model	JMA-9932-SA
Category	Marine Radar
Language	English