Parallel Indexing: How to Determine & Set Parallel Index Lines l PI Lines l RADAR l Passage Planning
Summary
TLDRThis video script explains the maritime navigation technique of Parallel Indexing, crucial for maintaining a safe distance from hazards or staying on course. Utilizing radar and charts, mariners set reference lines parallel to the ship's course for continuous monitoring. The tutorial covers setting these lines on both electronic and paper charts, understanding 'Not Less Than' (NLT) and 'Not More Than' (NMT) lines, and ensuring the vessel remains within navigable waters, even amidst GPS inaccuracies.
Takeaways
- 🚢 Parallel indexing (PI) is a navigation technique used by mariners to maintain a safe distance from hazards and stay on course.
- 📍 PI involves using radar and navigational charts to create reference lines parallel to the ship's course for continuous monitoring.
- 🏝️ A radar conspicuous object, such as a lighthouse or headland, is needed as a reference point for setting PI lines.
- 🚫 Buoys and shorelines with drying heights are not reliable reference points due to potential drift or changes in water level.
- 🛳️ PI should be determined during the passage planning stage and can be set using electronic navigational charts or paper charts.
- 📏 The distance from the planned track to the PI line is crucial and is measured to establish the PI distance.
- 📊 The 'Not Less Than' (NLT) and 'Not More Than' (NMT) lines are set to ensure the ship stays within navigable water, even if off the planned track.
- 📡 Setting PI lines on radar helps monitor the ship's position relative to the reference point and planned track.
- 🔍 The ship's actual position may differ from the GPS due to interferences, making PI a valuable tool for continuous position monitoring.
- ⚓ Knowing the ship is on safe water, even if not along the planned track, is the primary objective of the PI technique.
- 🛣️ The NLT and NMT lines create a corridor of navigable water, ensuring the ship remains within safe limits even if off course.
Q & A
What is parallel indexing in navigation?
-Parallel indexing is a technique used by mariners to maintain a safe distance from navigational hazards or to ensure that a vessel stays on a desired track by using radar and electronic or paper navigational charts to create reference lines parallel to the ship's course.
What is the abbreviation for parallel indexing?
-Parallel indexing is commonly known as PI.
What are the prerequisites for setting up parallel indexing?
-Parallel indexing should be determined during the passage planning stage, and it requires the use of a radar conspicuous object as a reference point, which provides strong radar echoes like lighthouses, harbor walls, headlands, and large cliffs.
Why can't buoys and other floating objects be used as reference points for parallel indexing?
-Buoys and other floating objects cannot be used as reference points because they might drift away anytime, which makes them unreliable for setting parallel index lines.
What does the color green on charts indicate in the context of parallel indexing?
-The color green on charts indicates shoreline with drying heights, which are areas exposed at low tide but submerged at high tide, making them unreliable as reference points for parallel indexing.
How is the distance for the parallel index line measured?
-The distance for the parallel index line is measured from the planned track to the parallel index line, which is the PI distance.
What are the not less than (NLT) and not more than (NMT) lines in parallel indexing?
-The not less than (NLT) and not more than (NMT) lines are additional parallel index lines set in the radar to determine the safe navigable water corridor on both sides of the planned track.
How can you set the NLT and NMT lines on a radar?
-To set the NLT and NMT lines on a radar, you determine the distance of navigable water on both sides of the planned track, draw lines parallel to the planned track, and then measure the distances from the planned track to establish the NLT and NMT lines.
What should a mariner do if the reference point in the radar moves towards the ship?
-If the reference point moves towards the ship, it indicates that the ship is off track to starboard, and a port helm should be executed to bring the ship back to the planned track.
How does parallel indexing help in continuous monitoring of a ship's position?
-Parallel indexing helps in continuous monitoring by allowing mariners to see if the reference point is along the PI line, indicating that the ship is within the planned track. If the reference point moves away from or towards the PI line, it signals that the ship is off track, and corrective action is needed.
Why is it important to periodically fix the ship's position even when using parallel indexing?
-It is important to periodically fix the ship's position because GPS can be subject to inaccuracies due to environmental and atmospheric interferences, and parallel indexing provides a visual confirmation of the ship's position relative to the planned track.
Outlines
🛳️ Parallel Indexing Technique in Navigation
This paragraph introduces the concept of parallel indexing (PI), a navigational technique used by mariners to maintain a safe distance from hazards and ensure adherence to a planned route. It involves using radar and navigational charts to create reference lines parallel to the ship's course. The method is crucial during the passage planning stage and requires setting PI lines with a specific distance from the planned track, using a radar conspicuous object as a reference. The paragraph also discusses the unreliability of certain reference points, such as buoys and shorelines with drying heights, due to their potential to change position. It emphasizes the importance of setting PI lines on radar for continuous monitoring of the vessel's track and introduces the terms 'not less than' (NLT) and 'not more than' (NMT) in relation to PI lines.
📍 Monitoring Ship's Position with Parallel Indexing
The second paragraph delves into the practical application of parallel indexing for continuous monitoring of a ship's position relative to its intended track. It explains how the movement of a reference point on radar indicates whether the ship is on track or off course, and the actions to be taken to correct the course if necessary. The paragraph also addresses the limitations of GPS positioning due to potential inaccuracies and emphasizes the primary objective of PI, which is to ensure the ship remains in safe waters. It further explains how to set the NLT and NMT PI lines on both paper and electronic charts to establish a navigable water corridor and determine the ship's safe position even when off track.
🚢 Safe Navigation with Not Less Than and Not More Than PI Lines
The final paragraph focuses on the importance of setting the NLT and NMT PI lines in the radar to ensure safe navigation. It provides a step-by-step guide on how to determine and set these lines based on the distance from the planned track and the navigable water on either side. The paragraph clarifies the difference between the NLT and NMT lines, explaining that the NLT line is set closer to the reference point, while the NMT line extends further into safe water. It also discusses the use of cross-track distance as an alternative method for setting these lines and emphasizes that as long as the reference point remains within the NLT and NMT lines, the ship is considered to be within navigable waters. The paragraph concludes with an animation demonstrating the ship's movement and the corresponding radar movements, reinforcing the concept that staying within these lines ensures safe navigation.
Mindmap
Keywords
💡Parallel Indexing
💡Navigational Hazard
💡Radar
💡Electronic Navigational Charts (ENC)
💡Index Lines
💡Radar Conspicuous Objects
💡Not Less Than (NLT) and Not More Than (NMT) Lines
💡Electronic Bearing Line (EBL)
💡Variable Range Marker (VRM)
💡Safe Water
💡Passage Planning
Highlights
Parallel indexing (PI) is a navigation technique for maintaining safe distance from hazards and staying on course.
PI uses radar and navigational charts to create reference lines for continuous vessel tracking.
The method should be determined during the passage planning stage for both electronic and paper charts.
Radar conspicuous objects like lighthouses and headlands are ideal for setting PI lines.
Buoys and shorelines with drying heights are not reliable reference points for PI.
Navigable and non-navigable water is distinguished by color coding on charts.
Safety parameters in the Electronic Navigational Chart (ENC) define navigable areas.
Mark non-navigable water as 'NOO' area during passage planning for both ENC and paper charts.
Create a parallel index line to the planned track using reference points.
Measure the PI distance from the planned track to the parallel index line.
Set the PI line on radar using tools provided in Electronic Chart Display and Information Systems (ECDIS).
Use the Electronic Bearing Line (EBL) and Variable Range Marker (VRM) for setting PI lines.
PI lines help monitor the ship's position and ensure it stays within the planned track.
PI technique is useful for continuous monitoring, especially when GPS may be inaccurate.
Set Not Less Than (NLT) and Not More Than (NMT) PI lines to define a safe navigable corridor.
NLT and NMT lines are calculated based on the PI distance and safe water distances.
Use cross track distance as an alternative method to determine NLT and NMT PI lines.
Ensure the reference point stays within NLT and NMT lines to maintain navigable water.
PI technique's primary objective is to maintain safe water, even if off the planned track.
Animation demonstrates ship movement and reference point tracking within PI lines.
Transcripts
parallel indexing is a navigation
technique used by Mariners to maintain a
safe distance from a navigational Hazard
or to ensure that the vessel stays on a
desired track this method involves using
radar and electronic navigational charts
or paper charts to create reference
lines or index lines parallel to the
ship's course to continuously monitor a
vessel's track to a predetermined
passage plan parallel indexing commonly
known as Pi should be determined during
the passage planning stage whether you
are using an electronic navigational
chart or a paper
chart assuming that this is our planned
route with a course of 31 9° true as per
the set safety parameters in our ENC we
have non-navigable water on both sides
of the planed
track we will use this island as our
reference point to set the parallel
index lines during our passage in this
area since this island is recognizable
in the
radar we need a radar conspicuous object
as a reference point to set our parallel
index
lines when we say radar conspicuous
objects these objects provide strong
radar Echoes making them prominent on
radar
displays examples of these objects are
lighthouses Harbor walls Headlands and
large
Cliffs buoys and other floating objects
cannot be used as reference points as
they might Drift Away
anytime Shoreline with drying Heights
are not reliable as a reference point
because this might be above the water
during the
passage the color green indicated in our
charts is the shoreline with drying
Heights these areas of the shore are
exposed at low tide but submerged at
high tide so this is not a reliable
reference point for parallel
indexing the shoreline of this island
has no drying Heights so here will be a
good spot to set our parallel index line
the blue color you can see around the
island and on the other areas of this
chart is not a drying height that blue
color distinguishes the navigable and
the non-navigable water based on the set
safety Contour in our
ENC I have made a video on how to
determine and set the safety parameters
in our etis kindly check the link in the
description before we set our parallel
index line
first we need to Mark our non-navigable
water as noo area it will be done
whether we are using an ENC or paper
charts during the stage of Passage
planning next create a line along the
selected reference point the line should
be parallel to the plan
Track This Is How We Do It using a paper
chart
but if you are using an electronic chart
use the pi tools provided in your
etis this is now our parallel index
line measure the distance from the plan
track to the parallel index line that is
your Pi distance in which in this chart
1.70 nautical
miles before I will discuss the not less
than or NLT and the not more than or nmt
lines let us set this parallel index
line first to the
radar upon approaching the island we
need to set the parallel index line to
our
radar the radar interface that appears
on your screen is an image from a radar
simulator it is set to relative motion
with North up the ship's GPS heading is
39° the island provides strong radar
Echoes making it an ideal spot to set
our par parallel index
lines we will use the pi tools provided
in this equipment to set our parallel
index line starting with
pi1 for the heading this is the
direction of the pi lines which is the
same as the plan track 31 9°
true for the distance it is the parallel
distance from the plan track and a set
parallel index line which is 1.70 Z
nautical
miles for the side it is the side to
where a conspicuous object is located
from the plan tra in this case it is
located on the starboard side of the
plan
track we have already set our parallel
index
line we can also use the electronic
bearing line known as ebl and the
variable range marker or vrm to set the
pi
line since the radar is set to relative
motion all all stationary objects will
appear to move in reciprocal direction
of the ship's
heading if the selected reference point
is along the parallel index line as it
moves in a reciprocal direction to
ship's course it means that the ship
stays within the plan track as she moves
in her intended
course as we know GPS is subject to some
interferences thus giving us position
inaccuracy this navigation technique is
very useful to navigator as it gives a
continuous monitoring of the ship's
position along the intended
track even though this technique is used
regular intervals of fixing the ship's
position should always be done as stated
in the passage
plan however knowing that the ship's
position is in the plan track this is
not the only objective of the parallel
indexing
technique knowing that the ship is still
ons Safe Water even if she is not along
the planed track is the primary
objective of this navigation
technique in this animation you can see
that the reference point is not along
the pi line it moves towards the ship it
means that the ship moves towards the
island so she is off track to
starboard a port Helm should be executed
until the reference point is along the
pi line as it goes back along the pi
line the ship's position is also along
the plan
track on the other hand as the reference
point moves away from the pi line the
ship is off track to
Port executing a starboard Helm will
bring the ship to its planned
track if we look at our ecta screen the
ship's position is still in safe
water but how are we sure that it is the
actual position of the vessel since our
ectis is integrated into our
GPS as we know GPS may be subject to
position error by a few or several
meters due to environmental and
Atmospheric
interferences the possible actual
position of the ship may be here or here
or she might be crossing the nogo area
to determine whether the ship is still
in Safe Water even if she is off
track we need to set the not less than
and the not more than Pi lines in the
radar to do this in your paper chart or
electronic navigational chart determine
the distance of of the navigable water
on both sides of the plan
track draw a line along the noggo area
parallel to the plan
track it should be done on both
sides then measure the distance from the
plan
track in this chart the room for safe
water on the starboard side of the plan
track is 0.80 nautical mile and on the
port side
0.95 nautical
mile this is now the corridor for the
navigable water as the ship passes along
this
area to determine the not less than or
NLT
line we need this parallel
distance so NLT is equal to Pi distance
minus the Safe Water distance from the
plan track towards the selected
reference point the pi distance is 1.70
minus the starboard Safe Water distance
which is
0.80 the not less than Pi line is 0.90
nautical
mile to find the not more than or nmt
line nmt is equal to Pi distance plus
the Safe Water distance from the plan
track away from the selected reference
point so Pi distance is
1.70 plus the Safe Water distance on the
port side which is
0.95 the not more than Pi line is 2.65
nautical
miles always remember that the not less
than Pi line distance should be measured
on the side of the plan track where the
reference point is
located and the not more than Pi line
distance is measured from the reference
point towards the Safe Water on the
other side of the plan
tra you can also use your cross trck
distance to determine the not less than
and not more than Pi
lines assuming that the cross trck
distance on both sides of the plan track
is 0.25 nautical
mile the not less than Pi distance is
1.45 nautical miles and the not more
than Pi distance is 1.95 nautical
miles in this video I did not use the
cross trck distance as the basis to
determine the not less than and the not
more than Pi lines since the objectives
of the parallel indexing technique are
not just to ensure that the vessel stays
on a desired track but also to maintain
a safe distance from a navigational
Hazard this animation shows that during
the risk of collision even if you go
beyond the cross trck distance there is
still enough navigable water to avoid
such
risk it is your preference to use the
cross trck distance as the basis to
establish your not less than and not
more than Pi lines
let us set those Pi lines in the
radar for the not less than Pi line we
will set it along the
pi2 all Pi lines have the same heading
as the plan track which is 31
9° the NLT distance is 0.90 nautical
mile and the location of our reference
point is on the starboard side of the
plan
track the not less than Pi line is
already dis
blade let us set the knot more than line
in
pi3 the heading is 31
9° the distance is 2.65 nautical
miles and the side is starboard side
since the location of the reference
point is on the starboard side of the
plan
track the not more than Pi line is
already displayed in the radar
screen the distance set in the radar is
based on approximation since this is
just an animation I am not using the
actual
radar do not be confused about the set
Pi line on the radar and the Drawn Lines
on both sides of the plan
track those lines are drawn in order to
establish the not less than and not more
than Pi
lines if you want to set the pi lines in
your etis it should be the same as the
set Pi lines in the
radar let us take out this Pi line along
the reference point
when the ship is going to starboard from
the planed track the reference point
moves closer to not less than Pi
line and when the ship is going to Port
from the intended track the reference
point moves closer to not more than Pi
line as long as the reference point
stays inside the not less than and the
not more than lines the ship is within
the navigable
water let us animate it again showing
the ship movement in the
chart the object in the radar moves in a
reciprocal direction of the ship's
movement and as long as the reference
point stays within the not less than and
the not more than Pi lines the ship
stays with the navigable
water that's all for now I hope you find
this video helpful thank you for
watching bye
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