Parallel Indexing: How to Determine & Set Parallel Index Lines l PI Lines l RADAR l Passage Planning

Summary

This 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

00:00

🛳️ 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.

05:01

📍 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.

10:03

🚢 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.

Keywords

💡Parallel Indexing

Parallel Indexing, also known as PI, is a navigation technique used by mariners to maintain a safe distance from hazards or to ensure adherence to a predetermined course. It involves setting reference lines parallel to the ship's course using radar and navigational charts. In the video, PI is crucial for monitoring the vessel's track and ensuring it stays within the safe navigable water, as demonstrated by setting PI lines during the passage planning stage.

💡Navigational Hazard

A navigational hazard refers to any obstacle or condition that could pose a risk to a vessel's safe passage. In the context of the video, maintaining a safe distance from such hazards is a primary objective of using parallel indexing. The script mentions non-navigable water on both sides of the planned track, which are considered hazards that the PI technique helps to avoid.

💡Radar

Radar is a system that uses radio waves to detect and locate objects, such as land masses or other vessels. In the video, radar is essential for setting and monitoring parallel index lines. It provides strong echoes from radar conspicuous objects, which are used as reference points for the PI lines, ensuring the vessel's position is accurately tracked.

💡Electronic Navigational Charts (ENC)

ENCs are digital charts that provide essential navigational information and are used in conjunction with electronic chart display and information systems (ECDIS). The script explains how to use ENC to set safety parameters and create reference lines for parallel indexing, emphasizing the importance of these charts in modern navigation practices.

💡Index Lines

Index lines are reference lines created during the parallel indexing process. They run parallel to the ship's course and are used to continuously monitor the vessel's track. In the video, setting index lines is a key step in the PI technique, helping mariners to keep the vessel on the desired track or maintain a safe distance from navigational hazards.

💡Radar Conspicuous Objects

Radar conspicuous objects are those that provide strong radar echoes, making them easily identifiable on radar screens. Examples given in the script include lighthouses, harbor walls, and headlands. These objects are critical for setting PI lines as they serve as reliable reference points during navigation.

💡Not Less Than (NLT) and Not More Than (NMT) Lines

NLT and NMT lines are part of the PI technique, defining the minimum and maximum distances from the planned track to ensure safe navigation. The script explains how to calculate these distances based on the PI distance and the safe water distance, creating a corridor of navigable water that the vessel should stay within.

💡Electronic Bearing Line (EBL)

An EBL is a tool used in conjunction with radar to determine the bearing of an object relative to the ship. In the video, the EBL, along with the variable range marker (VRM), is mentioned as a method to set PI lines, further illustrating the integration of electronic tools in modern maritime navigation.

💡Variable Range Marker (VRM)

The VRM is a tool on radar systems that allows mariners to measure the distance to an object. The script describes using the VRM to set PI lines, emphasizing its utility in determining the precise distance from the ship to the reference point for the PI technique.

💡Safe Water

Safe water refers to areas that are navigable and free from hazards. The script discusses the importance of maintaining the vessel within safe water, even if it deviates from the planned track. The PI technique is used to ensure that the vessel remains within these safe areas, as demonstrated by setting NLT and NMT lines to define a navigable corridor.

💡Passage Planning

Passage planning is the process of preparing for a vessel's journey, including determining the route, setting safety parameters, and anticipating potential hazards. The script highlights that PI should be determined during the passage planning stage, whether using ENC or paper charts, to ensure a safe and efficient voyage.

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