Restricted visibility lrg

© Grunt Productions 2007
RESTRICTED VISIBILITY
NAVIGATION
2008
A brief by Lance Grindley

Collision Avoidance In
Restricted Visibility

Collision Avoidance In
Visibility may be restricted by heavy rain,
snow, blown spray, low cloud, mist and fog,
and in some parts of the world blown sand,
and smoke.
Fog is defined as excess water vapor in the
air, reducing visibility to 1 nautical mile or
less.

Rule 19
Conduct of Vessels in

(a) This Rule applies to vessels not in
sight of one another when navigating
in or near an area of restricted
visibility.

(b) Every vessel shall proceed at a safe
speed adapted to the prevailing
circumstances and conditions of
restricted visibility. A power-driven
vessel shall have her engines ready for
immediate maneuver.

(c) Every vessel shall have due regard
to the prevailing circumstances and
conditions of restricted visibility when
complying with the Rules of Section I
of this Part.

The rules of Section 1 apply in any condition of
visibility. The particular rules are those
appertaining to:
5. Lookout,
6. Safe Speed
7. Risk of Collision
8. Action to Avoid Collision
9. Narrow Channels
10. Traffic Separation Schemes.

(d) A vessel which detects by radar
alone the presence of another vessel
shall determine if a close-quarters
situation is developing and/or risk of
collision exists.

If so, she shall take avoiding action in
ample time, provided that when such
action consists of an alteration of
course, so far as possible the
following shall be avoided:

(i) an alteration of course to port for a
vessel forward of the beam, other than
for a vessel being overtaken,

(ii) an alteration of course towards a
vessel abeam or abaft the beam.

(e) Except where it has been
determined that a risk of collision does
not exist, every vessel which hears
apparently forward of her beam the fog
signal of another vessel, or which
cannot avoid a close-quarters situation
with another vessel forward of her
beam, shall reduce her speed to the
minimum at which she can be kept on
her course.

She shall if necessary take all her way
off and in any event navigate with
extreme caution until danger of
collision is over.

Navigation In Restricted
Visibility

Navigation
• It is important that during restricted visibility,
that the position of the vessel is known at all
times
• This is especially because of the lack of any
visual references, unless the vessel is within
sight of a navigational aid.

Navigation
• This is also due to the lack of situational
awareness that could come about about
using the head up display on the radar, and
maneuvering as required by the Collision
Regulations to avoid risk of collision.

Parallel Indexing
• The principal
method of
monitoring
navigation in
restricted visibility
is the use of
parallel indexing

185
T
150
T
0.3 nm
0.3 nm
0.2 nm

Parallel Indexing
• The Variable Range
Marker is first set up on
the same distance as is
required to safely pass off
the radar conspicuous
object being used.
• In the example it is set up
0.3nm
• This is known as the
cross index range

Parallel Indexing
• The Electronic Bearing
Line is set up on the same
bearing as the course that
is required to be made
good

Parallel Indexing
• It is important that the radar conspicuous
objects used in parallel indexing are positively
identified from the chart or chart plotter and
checked on the radar.
• If parallel indexing is attempted on a moving
object, it will lead you off course and possibly
into danger.

Parallel Indexing
• 1. The vessel is steered,
so as to bring the radar
conspicuous target
against the Electronic
Bearing Line.

Parallel Indexing
• If the target crosses and
comes inside the
Electronic Bearing Line
alter to starboard to
increase the distance off.
• If the target moves further
away from the Electronic
Bearing Line, alter to port
to put it back on.

Parallel Indexing
• 2. The course is steered
to keep the radar target
on the line.

Parallel Indexing
• 3. The vessel is now
approaching the alteration
of course point.
• The next course is 150 T,
and cross index range
0.3’ .

Parallel Indexing
• 4. At this stage short of a
catastrophic failure, the
vessel will be safe, and
the parallel indexing for
the new course can be
set up

Parallel Indexing
• 5. Set up the new cross
index range (0.3 nm) on
the Variable Range
Marker, and then change
the bearing of the
Electronic bearing line to
the new course (150 T)
and rest it against the
Variable Range Marker
ring

Parallel Indexing
• 6. When the Electronic
Bearing Line on its new
bearing of 150 T is about
to come clear of the
conspicuous object, alter
course of the vessel to
150 T

Parallel Indexing
• 7. As before, steer the
course to keep the
conspicuous radar object
on the Electronic Bearing
Line

Parallel Indexing
• 8. Before the radar
conspicuous object No.1
disappears astern, have
available the new cross
index range of Radar
Conspicuous Object 2
available (0.2 nm)

Parallel Indexing
• 9. Set new cross index
range on Variable Range
Marker, and move
Electronic Bearing Marker
on bearing against
Variable Range Marker
ring.
• Steer to line as before

Parallel Indexing
• The use of parallel indexing need not be
confined to restricted visibility, but may be
used in clear visibility as well.

Monitoring Course
• An additional method available for
monitoring course is to preset routes into the
chart plotter.
• These waypoints and routes should be
preset into the chart plotter.
• The routes should then be verified during the
periodic training so that there is complete
confidence in these routes.

Monitoring Course
• The routes can then be used and relied upon
in case of unexpected restricted visibility,
night time navigation, and in transit on
training or during an incident.

Sound Signals in Restricted
Visibility

Visibility
• Rule 35
• In or near an area of restricted visibility,
whether by day or night, the signals
prescribed in this Rule shall be used as
follows:

Visibility
• (a) A power-driven vessel making way
through the water shall sound at intervals of
not more than 2 minutes one prolonged blast.

Visibility
• (b) A power-driven vessel underway but
stopped and making no way through the
water shall sound at intervals of not more
than 2 minutes two prolonged blasts in
succession with an interval of about 2
seconds between them.

Visibility
• (c) A vessel not under command, a vessel
restricted in her ability to maneuver, a vessel
constrained by her draught, a sailing vessel, a
vessel engaged in fishing and a vessel
engaged in towing or pushing another vessel
shall, instead of the signals prescribed in
paragraphs (a) or (b) of this Rule,

Visibility
sound at intervals of not more than 2 minutes
three blasts in succession, namely one
prolonged followed by two short blasts.

Visibility
• (d) A vessel engaged in fishing, when at
anchor, and a vessel restricted in her ability to
maneuver when carrying out her work at
anchor, shall instead of the signals prescribed
in paragraph (g) of this Rule sound the signal
prescribed in paragraph (c) of this Rule.

Visibility
• (e) A vessel towed or if more than one vessel
is towed the last vessel of the tow, if manned,
shall at intervals of not more than 2 minutes
sound four blasts in succession, namely one
prolonged followed by three short blasts.
When practicable, this signal shall be made
immediately after the signal made by the
towing vessel.

Visibility
• (f) When a pushing vessel and a vessel being
pushed ahead are rigidly connected in a
composite unit they shall be regarded as a
power-driven vessel and shall give the signals
prescribed in paragraphs (a) or (b) of this
Rule.

Visibility
• (g) A vessel at anchor shall at intervals of not
more than one minute ring the bell rapidly for
about 5 seconds. In a vessel of 100 meters or
more in length the bell shall be sounded in
the forepart of the vessel and immediately
after the ringing of the bell the gong shall be
sounded rapidly for about 5 seconds in the
after part of the vessel.

Visibility
• A vessel at anchor may in addition sound
three blasts in succession, namely one short,
one prolonged and one short blast, to give
warning of her position and of the possibility
of collision to an approaching vessel.

Visibility
• (h) A vessel aground shall give the bell signal
and if required the gong signal prescribed in
paragraph (g) of this Rule and shall, in
addition, give three separate and distinct
strokes on the bell immediately before and
after the rapid ringing of the bell. A vessel
aground may in addition sound an
appropriate whistle signal.

Visibility
• (i) A vessel of 12 meters or more but less
than 20 meters in length shall not be obliged
to give the bell signals prescribed in
paragraphs (g) and (h) of this Rule. However,
if she does not, she shall make some other
efficient sound signal at intervals of not more
than 2 minutes.

Visibility
• (j) A vessel of less than 12 meters in length
shall not be obliged to give the above
mentioned signals but, if she does not, shall
make some other efficient sound signal at
intervals of not more than 2 minutes.

Visibility
• (k) A pilot vessel when engaged on pilotage
duty may in addition to the signals prescribed
in paragraphs (a), (b) or (g) of this Rule sound
an identity signal consisting of four short
blasts.

These guys ran aground in poor visibility, the main
cause of the incident, amongst a number of errors,
was poor radar management

Restricted visibility lrg

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