IMU Navigational System and Equipment

8/6/2019 IMU Navigational System and Equipment

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BNA- 041

NAVIGATIONAL AIDS

AND ENVIRONMENTAL

PROTECTION

Block

NAVIGATIONAL SYSTEM AND EQUIPMENT

UNIT 1

Automatic Identification System 5

UNIT 2

Speed Measurement at Ships 27

UNIT 3Radar for Navigation 35

UNIT 4

Navigation by ARPA 53

UNIT 5

Electronic Aids 71


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NAVIGATIONAL AIDS AND ENVIRONMENTAL

PROTECTION

Navigational aids are important for ascertaining whether the ship is maintaining the

direction in which she has been steering and the distance which she is supposed to have

steamed and made good. It is also equally important that the voyages are executed without

any pollution damage to the environment.

This course deals with the above aspects as well as matters related to emergencies. It

also covers some of the recent developments which have taken place in carriage of cars and

containers and would be handy to the students who are sailing on car and containers

carriers.

Course comprises three blocks.

Block I deals with the Navigational Systems and equipment and the importance of their

correct use for safe navigation.

Block 2 deals with the hazard caused to the environment due to ship's points and how to

deal with those. It also covers information about containers, container handling and car

carriers.

Block 3 deals with all aspects of search and rescuer at Sea, ship Reporting systems and

contingency planning.


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NAVIGATIONAL SYSTEM AND EQUIPMENT

This block consists of 5 units.

Unit I introduces 'Automatic Identification System' (AID) which has been mademandatory for carriage by the IMO and discuss usefulness as a tool foravoiding carriag

and reporting various parameters of the ship to VIS.

Unit 2 deals with various methods of speed measurement on ships.

Unit 3 introduces methods for using Radar as an aid to navigation and describes

precautions required before standing the radar and when using its controls.

Unit 4 deals extensively with displaying modes collision, avoidance and positions fixing by

means of Automatic Radar Plotting Aids (ARPA).

Unit 5 deals with the Navigation equipment and Systems on board the ship.


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UNIT I AUTOMATIC IDENTIFICATION

SYSTEMS

Structure

1.1 Introduction

Objectives

1.2 Description of AIS

1.3 Carriage Rule Requirement

1A Components

1,5 AIS Information -- Ship's Data Content

1,6 Contents of Data Sent by VTS

1.7 Integrity Checks

1,9 Operation of AIS on Board

1.9 Inherent Limitations of AIS

1,10 Additional and Future Applications

1.11 Voyage Data Recorders

1.11.1 Preamble

1,11,2 What Can a VDR Do?

1-113 Rule Requirements

1,11.4 Definitions

1,11.5 Operational Requirements

1,11.6 Data Selection and Security

1.11.7 Performance Tests

1.11.9 Process of Dealing with Data

1,11.9 Data Items to be Recorded

1.11.10 Simplified Voyage Data Recorders

1,12 Summary

1.13 Answers to SAQs

1.1 INTRODUCTION

The Automatic Identification Systems (AIS) being a new system needs familiarisation and

understanding its need and limitations. As the name indicates AIS facilitates the

identification of ships and provides a tool for avoiding collisions, reporting variousparameters of the ship to Vessel Traffic Services (VTS) and to other ships in the vicinity.

The transmission of information as indicated below is automatic and the information

received can be either interpreted or displayed in various forms including radar or a

dedicated CRT Monitor.

Objectives

After studying this unit, you should be able to

describe the AIS as a Navigational Aid,

explain the mandatory carriage requirements,

describe its components,

describe the information transmitted by AIS,

describe information transmitted by VTS, 5


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Navigational System

and Equipment explain the integrity checks of the system,

handle the operation AIS on board,

describe inherent limitation of AIS and

explain the present and future applications of the system.

1.2 DESCRIPTION OF AIS

In the early stages of its use, it may be noted that:

AIS equipment is available from a number of manufacturers and manysoftware applications are possible.

The user should be familiar with the AIS in order to become competent inthe use of the system and of the displayed data for safe navigation.

Warning : The Officer of the Watch (OOW) should always be aware that other ships,and in particular leisure craft, fishing boats and warships, and some coastal

shore stations including Vessel Traffic Service (VTS) centres might not be

fitted with AIS. The OOW should always be aware that other ships fitted

with AIS as a mandatory carriage requirement might switch off AIS by

professional judgement of the master.

SOLAS regulation V/19 defines the mandatory carriage requirements as follows:

AIS has the Following Functionality

Provide automatically to appropriately equipped shore stations, other shipsand aircraft information, including the ship's identity, type, position,

course, speed, navigational status and other safety-related information;

receive automatically such information from similarly fitted ships; monitor

and track ships; and

Exchange data with shore-based facilities.Thus, AIS will become an important supplement to existing navigational systems

including radar. In general. data received via AIS will enhance the quality of the

information available to the OOW. AIS is an important tool to enhance situational

awareness of the traffic-situation to all users.

In particular, the purpose of AIS is to:

identify vessels;

assist target tracking;

simplify information exchange;

provide additional information to assist collision avoidance; and reduce verbal mandatory ship reporting.

It shall also:

receive automatically such information from similarly fitted ships;

monitor and track ships; and

exchange data with shore-based facilities.

Technical Description

AIS shall continuously transmit ship's own data to other vessels and VTS stations,

continuously receives data of other vessels and VTS stations, and displays this data.


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IMO SOLAS Convention Chapter V [2002] requires:

All ships of 300 gross tonnage and upwards engaged on international voyages and cargo ships of 500 gross tonnage

and upwards not engaged on international voyages and passenger ships, irrespective of size, shall be fitted with AIS,

as follows

AIS operates primarily on two dedicated VHF channels (AIS 1 -161,975 MHz

and AIS2 -162,025 MHz). Where these channels are not available regionally, the

AIS is capable of automatically switching to alternate designated channels.

The required ship reporting capacity according to the IMO performance standard

amounts to a minimum of 2000 time slots per minute (Figure 1.1). The ITU

Technical standard for the Universal AIS provides 4500 time slots per minute. The

broadcast mode based on a principle called STDMA (Self-organized Time Division

Multiple Access) that allows the system to be overloaded with 400 to 500% and

still provides nearly 100% throughput for ships closer than 8 to 10 NM to each

other in a ship to ship mode. In the event of system overload, only targets far away

will be subject to drop out in order to give preference to targets close by that are a

primary concern for ship-to-ship operation of AIS. In practice, the capacity of the

system is unlimited allowing for a great number of ships to be accommodated at

the same time.

Automatic IdentificationSystem

Vessel provides ID position,Course, heading, speed.

vessel receives information on

vessel, port data hazards in area

Figure .11 , AIS System Overview

When usedwith the appropriate graphical display, AIS enables provision of fast,

automatic and accurate information regarding risk of collision by calculating Closest

Point of Approach (CPA) and Time to Closest Point of Approach (TCPA) from the

position information transmitted by the target vessels.

A1S operates primarily on two dedicated VHF channels. Where these channels are

not available regionally, the AIS is capable of automatically switching to

designated alternate channels. In practice, the capacity of the system is unlimited

allowing for a great number of ships to be accommodated at the same time.

The AIS is able to "see" around bends and behind islands if the landmasses are not

too high. A typical value to be expected at sea is 20 to 30 nautical miles depending onantenna height. With the help of repeater stations, the coverage for both ship and

VTS stations can be improved. Information from operational AIS is

transmitted continuously and automatically without any intervention of the OOW. An

AIS shore station might want updated information from a specific ship, or

alternatively, might want to "poll" all ships within a defined sea area.

1.3 CARRIAGE RULE REQUIREMENT


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Navigational System

and EquipmentShips engaged on international voyages constructed before 1 July 2002.

(a) In the case of passenger ships and tankers not later than I July 2003.

(b) In the case of ships, other than tankers, of 50.000 gross tonnage andupwards not later than I July 2004.

(c) In the case of ships, other than tankers. of 10.000 gross tonnage andupwards but less than 50.000 gross tonnage, not later than I July 2005.

(d) In the case of ships, other than tankers, of 3.000 gross tonnage and upwards

but less than 10.000 gross tonnage, not later than I July 2006.

(e) In the case of ships, other than tankers, of 300 gross tonnage and upwardsbut less than 3.000 gross tonnage, not later than 1 July 2007.

(f) Ships not engaged on international voyages constructed before 1 July 2002,not later than 1 July 2008.

The administrations may exempt ships from the application of the requirements for AIS

when such ships will be taken permanently out of service within two years after the

implementation dates specified above.

1.4 COMPONENTS

In general, the AIS on board (Figure 1.1) consists of

Antennas;

One VHF transmitter;

Two multi-channel VHF receivers;

One channel 70 VHF receiver for channel management;

A central processing unit (CPU);

An electronic position fixing system, Global Navigation Satellite SystemGNSS receiver for timing purposes and position redundancy;

Interfaces to heading and speed devices and to other ship borne sensors;

Interfaces to radar/Automatic Radar Plotting Aids (ARPA), ElectronicChart System/Electronic Chart Display and Information System(ECS/ECDIS) and integrated navigation systems;

Built-In Integrity Test; and

Minimum display and keyboard to input and retrieve data.

GPS -ANTENNA

N

AIS Schematic

I ____a LONGi PANG

2 4 V I X Do

ECDIS

rut soon::::00100"Was

ALARMCiRCUIT

.'4_10 ---------i14

Figure 1.2 : AIS Schematic Showing Inputs/Outputs


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Automatic Identification

Connections to Other Navigational Display Systems System

With the integral minimum display and keyboard unit, the AIS would be able to beoperated as a stand-alone system. The AIS can also be connected either to anadditional dedicated AIS display unit and possibly one with a large graphicdisplay, or to an existing navigational system such as radar or an electronic chart butin the later case only as part of an integrated navigation system.

It is becoming common practice for pilots to possess their own portable

navigational equipment, which they carry on board. Such devices can beconnected to AIS equipment and display the targets they receive.

The Connection with Radio Communication Devices

AIS is provided with a two-way interface for connecting to long range radiocommunication equipment. Initially, it is not envisaged that AIS would be able tobe directly connected to such equipment. A shore station would first need to requestthat the ship makes a long range AIS information transmission. Any shipto-shorecommunication would always be made point-to-point, and not broadcast, and oncecommunication had been established, the ship would have the option of setting itsAIS to respond automatically to any subsequent request for a ship report, from

that shore station. Under regulation 11. 11 of SOLAS Chapter V, as amended, theparticipation of ships in IMO-adopted ship reporting systems should be free ofcharge to the ships concerned.

1.5 AIS INFORMATION - SHIP'S DATA CONTENT

The information transmitted by AIS from a ship includes three different types ofinformation:

Fixed or Static

Fixed or static information that is entered into the AIS on installation and need

only be changed if the ship changes its name or undergoes a major conversionfrom one ship type to another. These are

MMSI

Call sign and name

IMO Number

Length and beam

Type of Ship

Location of position fixing antenna

Those underlined would need to be changed when the ship changes its ownership

or name.

Figure 1.3 : Information Shown by AIS


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Navigational System

and Equipment

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Dynamic

Dynamic information is automatically updated from. the ship sensors connected to AIS:

thee include:

Ship's position with accuracy indication and integrity status

Position Time stamp in UTC

Course over ground (COG)

Speed over ground (SOG)

Heading

Rate of turn (ROT)

Navigational status information has to be manually entered by the OOW and

changed, as necessary, for example: I

underway by engines

at anchor

not under command (NUC)restricted in ability to manoeuvre (RIATM)

moored

constrained by draught

aground

engaged in fishing

underway by sail

Voyage

Voyage related information that might need to be manually entered and updated

during the voyage in the form of free format short text messages addressed either to

a specific addressee or broadcast to all ships and shore stations.

The data is autonomously sent at different update rates and the update rates

depend on the speed,e.g. when the ship is doing > 14 knots the rate would be

2 seconds while when doing < 14 knots and when on a steady

course it shall be

12 seconds. The rate varies when altering course also. When stopped or when at

anchor, the rate shall be 3 minutes.

Static and voyage related data

is

updated every 6 minutes or on request (respondsautomatically without user action).

Short Safety Related Messages

AIS has the capability of sending short safety related messages in a Fixed or free9format text messages addressed either to a specified destinat

ion (MMSI) or a] I ships

in the area. Their content should be relevant to the safety of navigation, e.g. an

iceberg sighted or a buoy not on station. Messages should be kept as short as

possible. The system allows up to 158 characters per message but the shorter the

message the easier it will find free space for transmission. These messages are not

further regulated, to keep all possibilities open.

Operator acknowledgement may be requested by a text message. Short safety

related messages are only an additional means to broadcast maritime safety

information. Whilst their importance should not be underestimated, the usage ofSuch

requirements t

such short safety related message does not remove any of the requirements of the

the Global Maritime Distress Safety System (GMDSS) and SOLAS Chapter V,


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Regulation 31 (Danger messages and the practice of transmission of such System

messages by VHF should be continued).

Confidentiality

When entering any data manually consideration should be given to confidentiality

of this information.

1.6 CONTENTS OF DATA SENT BY VTSPseudo AIS information is information about vessels which are not carrying AIS and

which are tracked only by VTS radar, via the AIS to vessels equipped with AIS. Any

pseudo AIS target broadcast by VTS should be clearly identified as such. Particular care

should always be taken when using information that has been relayed by a third party.

Accuracy of these targets may not be as accurate as actual directly received targets and the

information content may not be as complete.

Text messages include short messages either to one ship, all ships or ships within a

certain range or in a special area, e.g.:

(Local) navigational warnings; Traffic management information; and

Port management information.

A VTS operator may request by a text message an acknowledgement from the ship's

operator.

Note: The VTS will continue to communicate via VHF. The importance of verbal

communication should not be underestimated. This is important for the VTS

operator to:

Assess the vessels communicative ability; and

Establish the direct communication link, which could be needed in criticalsituations.

SAQ 1

(a) What information is available from use of AIS and to what extent cannavigators rely on this information in the early stages?

(b) What channels does AIS operates and what happens if these channels arenot available in the area?

(c) How is the information relating to the course and speed updated by AIS?

(d) Why is the AIS connected to the ships communication system?

1.7 INTEGRITY CHECKS


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Integrity relates to the trust, which can be placed in the correctness of the information

supplied by the navigation system. Integrity includes the ability of a system to provide

timely and valid warning to the user. One would expect the integrity to be about 99.9 per

cent. However, when fixing position using more than one input, e.g. GPS, radar and AIS, II

Navigational System

and Equipmentwhich one is more accurate than the other? Which one does the navigator choose as its

primary source?

Such integrity is provided through:

A built-in integrity test (BIIT) running continuously or at appropriateintervals;

Monitoring the availability of the data;

An error detection mechanism of the transmitted data; and

Error checking of the received data.

If no sensor is installed or if the sensor (e.g. the gyro) fails to provide data, the AIS

automatically transmits the "not available" data value. However, the integrity check

cannot validate the contents of the data received by the AIS.

1.8 OPERATION OF AIS ON BOARD

Operation of the Transceiver Unit Activation

AIS should always be in operation. It is recommended not to switch off AIS duringport stays, because-of the valuable information to port authorities. If the master

believes that the continual operation of AIS might compromise the safety or

security of his ship, he may switch off the AIS.

The master should, however, restart the AIS as soon as the source of danger has

disappeared. This might be the case in sea areas where pirates and armed robbers are

known to operate. Actions of this nature should always be recorded in the ship's

logbook. If the AIS is shutdown, static data and informationagerelated

inforationvoyag

stored. Restart is done by switching on the power to the AIS unit. Ship's

own data will be transmitted after a two-minute initialization period.

Manual Input of Data

The OOW should manually input at the start of the voyage and whenever changes

occur the following information using the input device such as a keyboard

Ship's draught;

Hazardous cargo;

Destination and ETA;

Route plan (way-points);

The correct and actual navigational status, and

Safety related short messages.

Correctness of Information

To ensure that static information is correct and up-to-date, the OOW should check the

data whenever there is a reason for it. As a minimum, this should be done once per

voyage or once per month whichever is shorter. The data may be changed only by the

master or by an authorized person.

The OOW should also check the following dynamic information:

Ensure that positions are given according to WGS 84;

Ensure that the speed over ground is provided; and

Verify the sensor information periodically.


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After activation an automatic built-in integrity test (BIIT) is performed. In case of

any AIS malfunction an alarm is provided and the unit stops transmitting.

The quality or accuracy of the ship sensor data input into AIS would not, however, be

checked by the BIIT circuitry before being broadcasted to other ships and shore

stations. The ship should, therefore, carry out regular routine checks during a voyage

to validate the quality of the information being transmitted, and the frequency

of those

checks would need to be increased in coastal waters.

4 Display of AIS DataThe AIS provides data that can be presented on the minimum display or on any

suitable display device as described in Section 3.3.

Minimum Display

The display provides three lines of data. Each line displays at least bearing, range

and name of a selected ship. Other data of the ship can be disp'ayed by horizontal

scrolling of data, but scrolling of bearing and range is not possible. Vertical scrolling

will show all the other ships known to the AIS.

Graphical Display

If the AIS information is presented graphically, it should ideally be consistent andshould consist of the following:

Sleeping Target

A sleeping target indicates only the presence of a vessel equipped with AIS

in a certain location. No additional information is presented until activated

thus avoiding information overload.

Activated Target

If the user wants to know more about a vessels motion, he has simply to

activate the sleeping target. The display shall show immediately:

Selected Target

if the user wants detailed information of a target (activated or sleeping), he

may select it. Then, the data received as well as the calculated CPA and TCPA

values will be shown in an alpha-numeric window. The special navigation

status will also be indicated in the alpha - numeric data field and not together

with the -target directly.

Dangerous Target

If an AIS target (activated or not) is calculated to pass pre-set CPA and TCPA

limits, it will be classified and displayed as a dangerous target and an alarm

will be given.

Lost Target

If an AIS signal of any AIS target at a distance of less than a preset value is

not received, a lost target. symbol will appear at the latest position and an

alarm is given.

Use of AIS

When using the AIS in the ship-to-ship mode for anti collision purposes, the OOW

should carefully note the information in the ensuingparagraphs:


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Navigational System

and EquipmentNote that AIS is an additional source for navigational information. AIS does not

replace, but supports navigational systems such as radar target tracking and VTS.

The use of AIS does not negate the responsibility of the OOW to comply with all

COLREG requirements, in particular maintaining a proper lookout, proceeding at a

safe speed and radar observation.

AIS Tracking is

Highly accurate;

Provided in near real-time;

Capable of instant presentation of target course alterations;

Not subject to target swap;

Not subject to target loss in clutter;

Not subject to target loss due to fast manoeuvres; and

Able to look around bends and behind islands.

However, the user should not rely on AIS as the sole information system. He has

to use all safety-relevant information available. AIS is just one of a number of aids

to safe navigation available to the OOW. The presence on board of AIS should nothave any special impact on the composition of the navigational watch, which

should be determined in accordance with the STOW Code.

When assessing the navigational situation without AIS, the OOW appraises other

ships or targets relative to own ship. AIS information is geographically based

(ground stabilised) and represents the actual navigational movement of a ship in

near-real time. Care should, therefore, be taken when attempting to match AIS

information with that which has been observed from the ship either visually or by

radar.

Once a ship has been detected, AIS can assist in tracking it as a target. By

monitoring the information broadcast by that target, its actions can also be readilymonitored. Changes in heading and course are, for example, immediately

apparent, and many of the problems common to tracking targets by radar, namely

Clutter, target swap as ships pass close by and target loss following a fast

manoeuvre, do not affect AIS.

AIS can also assist in the identification of targets, by name or call sign and by ship

type and navigational status. The ability to identify targets should not, however, be

used to use VHF to resolve collision situations. Further, ships should not agree to

collision avoidance actions that contravene the rules contained in the COLREGS.

Complying with the COLREGS should not necessitate the use of VHF, or any other

means of ship-to-ship communication, other than the display of appropriate lights and

shapes. Indeed, resorting to verbal VHF communications cations might lead to languagemisinterpretations and should be avoided.

In developing close-quarter situations, the availability of AIS information should also

not encourage any ship to stand-on for longer than would be usual where only visual

or radar observations are available. Early and substantial action to keep well clear of

another vessel, as required by the COLREGS should always be taken.

AIS may calculate collision avoidance parameters such as CPA and TCPA. The

OOW should be aware that such parameters calculated by AIS might differ to

those -calculated by radar, for the same target. When using radar to match AIS and

radar targets, it is important to switch the radar to ground stabilised mode to compare

radar and AIS target vectors.


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Figure 1.4 : AIS and ARPA Targets on Typical Radar -Display

Symbols

The user should be familiar with the symbology used in the graphicaldisplay provided,

1.9 INHERENT LIMITATIONS OF AIS

The Officer of the watch (OOW) should always be aware that otherships, and in particular leisure craft, fishing boats and warships, and some

coastal shore stations including Vessel Traffic Service (VTS) centres mightnot be fitted with AIS.

The OOW should always be aware that other ships fitted with AIS as amandatory carriage requirement, might switch off AIS by professionaljudgement of the master. In other words, the information given by the AISmay not be a complete picture of the situation around the ship. It may benoted that AIS may not be supported by the older generation radars.

The users must be aware that transmission of erroneous informationimplies a risk to other ships as well as their own. The users remainresponsible for all information entered into the system and the information

added by the sensors.

The accuracy of AIS information received is only as good as the accuracyof the AIS information transmitted.

The OOW should be aware that poorly configured or calibrated shipsensors (position, speed and heading sensors) might lead to incorrectinformation being transmitted. Incorrect information about one ship displayedon the bridge of another could be dangerously confusing,

9

It would be prudent for the OOW not to assume that the informationreceived from other ships is of a comparable quality and accuracy as that

which might be available on own ship.


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When engaged on international voyages, unless exempted shall be fitted with a Voyage System

Data Recorder (VDR) as follows :

passenger ships constructed on or after 1 July 2002;

ro-ro passenger ships constructed before 1 July 2002 not later than thefirst annual survey after 1 July 2002;

passenger ships other than ro-ro passenger ships constructed before 1 JulyC>

2002 not later than 1 January 2004; and

ships, other than passenger ships, of 3,000 gross tonnage andupwards constructed on or after 1 July 2002.

1.11.1 Preamble

Voyage data recorders requirement is a new rule under Chapter V of SOLAS. It requires

VDRs to be fitted to all new ships of 3000 GRT and over, and existing passenger ships,

when engaged on international voyages. The VDR or the marine "black box" is equipped

to record key navigational information. Such information can then be used to build up an

accurate picture of events preceding an accident and enable investigators to establish the

causes.

1.11.2 What Cana VDR Do?

In an October 10, 1998, article, Loyds List wrote:

"Ironically, of all the technical requirements that are designed to prevent accidents

(although most are designed to minimize their consequences), the provision of 'black boxes'

is something that only comes into its own after the incident. Not that there is no

commercial reason (value) for their adoption on ferries. Voyage event recorders can

monitor whatever is required, from the way a ship is handled, to the performance of the

machinery and its forensic employment must be considered almost incidental. They have

proved themselves in operation in a number of areas, from the optimization of fuel

economy measures to the defence of the owner in the event of an incident. And although it

can be argued that they scarcely affect safety directly, the lessons they produce certainly

do."

The purpose of a voyage data recorder is to maintain a store, in a secure and retrievable

form, of information concerning the position, movement, physical status, command and

control of a vessel over the period leading up to and following an incident having an

impact thereon. Information contained in a VDR should be made available to both the

administration and the ship-owner. This information is for use during any subsequent

investigation to identify the cause(s) of the incident.

Voyage event recorders can monitor whatever is required, from the way a ship is handled,

to the performance of the machinery and its use in an accident must be considered almost

incidental. They have proved themselves in operation in a number of areas such as:

the optimization of fuel economy, and

the defence of the owner in the event of an incident.

Although it can be argued that they scarcely affect safety directly, the lessons they

produce certainly do.

Fulfil "ISM Responsibilities"

A survey found that a number of operators view VDR systems as valuable tools tc

achieve the objectives of the ISM Code. P & 0 Lines, which is considered a pioneer

in the development and use of VDRs, has been using VDR systems for years to fulfilits ISM responsibility to provide management oversight of its fleet. A P & 0

subsidiary reports that it has 120 VDR units throughout its fleets of Ro-Ro ferries,

bulkers, tank ships, and other vessels. VDR systems have been voluntarily installed

on BP tankers, Conoco tankers, Chevron tankers and Holland17


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Navigational Systemand Equipment

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America Line passenger ships. In addition, the US Navy has an experimental project

with a system called "Smart Ship", which, among other functions, records radar

data.

Operational Efficiency

Companies are finding that, in addition to the obvious ISM and post-accident value

of VDR information, they can realize a payback in their fleet operations by using the

data to monitor the various systems on board. In a 1998 article written for DNV

FORUM ISSUE No. 2, Performance Monitoring Enhances Operational Efficiency,

Stuart Brewer endorses the benefits of maintaining vital machinery data in order toreview main engine performance data and to make adjustments as needed. Mr.

Brewer's article states:

"There are several benefits in maintaining performance (records) of the main

engine. As an example: modern two-stroke slow-speed engines are fitted with

variable injection timing equipment (VIT). Correct functioning of the VIT is

essential for good engine performance and by monitoring performance as laid down

in the DNV program we can detect maladjustment's and make the necessary

corrections. A correctly adjusted engine ensures better fuel economy, more

operating hours per cylinder, and better overall engine condition and economy. It

also results in cleaner exhaust gases and reduced harmful emissions. We see

performance monitoring as a means to optimize the engine's condition and itsmaintenance intervals."

Based on the results from its "New Machinery Project" and in line with the

procedures from its pilot test ship program, the DNV is planning to launch a new,

voluntary class notation. When the DNV was asked if it saw any use for such a new

notation, a representative replied that such a notation would be much like a "stamp

for good housekeeping", conveying to the market that from this ship you could

expect reliable performance, good fuel economy and fewer unexpected costs in

machinery maintenance.

.41 the very early stages of satellite communications, a well known shipping

company used to get the engine room parameters transmitted to the head officecomputers on a daily basis. The data was then analysed and the company,

intimated the ship if some of the machinery parameters needed correction!

Accident Investigation and Reduction

In its first review of maritime safety, the European Transport Safety Council

(ETSC) estimates that 140 fatalities occur annually in European sea transport and

observes that the safety.culture and safety regulations must be improved. The ETSC

identifies priority measures for accident reduction. Among these measures are a

systems approach to safety and the need for better statistical information,

specifically a European Union (EU) database and VDRs and an independent

maritime accident investigation agency. Other needs or changes that the ETSC

identifies include the following:

a common education and training framework,

international medical/psychological standards,

a legal maximum blood alcohol level,

fatigue reduction measures,

on-board facilities,

improved communications technologies,

safety guidelines in and near ports,

bulk carrier and ro-ro ferry design,

survival capability of high speed and

Passenger ferry survivability.


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VDRs in International Investigations

On November 27,1997, the IMO adopted IMO Resolution A.849(20), Code for the

Investigation of Marine Casualties and Accidents, which the US Coast Guard

endorsed and disseminated inNavigation and Vessel Inspection Circular Number: 5-

98. In issuing NVIC 5-98, the Coast Guard summarized the IMO action as follows:

The international community has increasingly become aware of the benefits of

cooperating in casualty investigations given the international nature of shipping and

the fact that Flag-State interests often overlap port-state interests. As a result, a

series of IMO resolutions have addressed international cooperation in increasing

depth, and many valuable cooperative investigations have resulted in the past 10

years. Drawing on the experience of these cooperative investigations, and

recognising the opportunity to improve safety through information sharing, the IMO

member states developed a Code for the investigation of marine casualties and

incidents. The Code provides a standard international approach to investigations and

enhances the existing cooperative frameworks.

The Code includes an appendix, Guidelines to assist investigators in the

implementation of the Code,which provides the following guidance on VDRs

Where information from a VDR is available, in the event that the State conducting

the investigation into a casualty or serious incident does not have appropriate

facilities for readout of the VDR, it should seek and use the facilities of another

State, considering the following:

(a) The capabilities of the readout facility;

(b) The timeliness of the availability of the facility; and

(c) The location of the readout facility.

The installation of VDRs is an important safety issue for all marine operators,

especially for operators of passenger vessels. Automatic data recording devicesprovide crucial information for accident investigation and play a key role in

identifying and addressing causal factors. While it can be argued that the VDR may

not be a first line safety tool, such as a life jacket or fire extinguisher, it certainly has

great value in ensuring that a vessel is operated safely, that its gear is performing as

intended, and that the crews are performing as required by regulation, company

policy, and the general rules of "good seamanship".

VDRs in Port State Control Compliance

In a 1997 article forIMO News, the senior deputy director of the IMO's Maritime

Safety Division states on Port State control:

"The inspection of foreign flag vessels visiting national ports has been describedas the last safety net in marine safety. In an ideal world, Port State control would not

exist, but when shipowners, classification societies, insurers or Flag administrations

have in one way or another failed to do their job, Port State control comes onto the

scene. Port State control is recognized as being a step in the right direction towards

the eradication of substandard ships, when it is carried out in accordance with IMO

Assembly resolutions and recommendations."

It is only natural that government agencies and their delegated inspectors employ

the information gathered by the VDR in conducting the various Port State

requirements, which includes enforcing the ISM Code and ensuring that a vessel

complies with navigation and other safety regulations and applicable pollution

prevention regulations (IMO/MARPOL).


19/87


System

20

Navigational System V DR as a Management Tool

and Equipment Me VDR provides the ves,,ci operator and owner with information that can be used

to better manage the vessels operation, thus providing key information that can be

used to improve traffic routing, manage hull stress conditions, and better manage

fuel consumption. The VDR also provides the owner/operator with a

comprehensive record of what occurred in an event, thereby assisting in the event

of some tort action. The management benefits derived from installing a VDR

system would quickly offset the cost of its installation.

1.11.3 Rule Requirements

Ships on international voyages are to be fitted with VDRs according to timetable given

(to assist in casualty investigations, ships) as follow!

(a) passenger ships constructed on or after I July 2002;

(b) ro-ro passenger ships constructed before I July 2002 not later than the firstsurvey on or after I July 2002;

(c) passenger ships other than ro-ro passenger ships constructed before1 July 2002 not later than 1 January 2004; and

(d) ships, other than passenger ships, of 1,000 gross tonnage and upwardsconstructed on or after I July 2002.

1.11.4 Definitions

Voyage Data Recorder (VDR)

Voyage data recorder means a complete system, including any items required to interface

with the sources of input data, for processing and encoding the data, the final recording

medium in its capsule, the power supply and dedicated reserve power source.

Sensor

Sensor means any unit external to the VDR, to which the VDR is connected and

from which it obtains data to be recorded.

Final Recording Medium

Final recording medium means the item of hardware on which the data is recorded

such that access to it would enable the data to be recovered and played back by use

of suitable equipment.

Playback Equipment

Playback equipment means the equipment, compatible with the recording medium

and the format used during recording, employed for recovering the data. It

includes also the display or presentation hardware and software that are

appropriate to the original data source equipment.

Dedicated Reserve Power Source

Dedicated reserve power source means a secondary battery, with suitable

automatic charging arrangements, dedicated solely to the VDR. of sufficient

capacity to operate it.

Administrations may exempt ships, other than ro-ro passenger ships, constructed

before I July 2002 from being fitted with a VDR where it can be demonstrated that

interfacing a VDR with the existing equipment on the ship is unreasonable and

impracticable.


20/87

21

There is no requirement at present for ships under 3000 gt, or for existing shipsother than passenger ships, to be fitted with VDRs. Owners of all vessels are,however, encouraged to fit VDRs, when practicable to do so, in order to assist inthe investigation and identification of the causes of accidents and other incidents. Aseparate standard for a simplified VDR is given below:


R e ml e Alarm Data Caosolf,

Typical VDR Schematic diagram

Figure 1.5: Typical VDR Schematic Diagram

1.11.5 Operational Requirements

(a) The VDR should continuously maintain sequential records of pre-selecteddata items relating to the status and output of the ship's equipment, andcommand and control of the ship.

(b) To permit subsequent analysis of factors surrounding an incident, the methodof recording should ensure that the various data items could be co-related indate and time during playback on suitable equipment.

(c) The final recording medium should be installed in a protective capsulewhich should meet all of the following requirements :

(i) be capable of being accessed following an incident but secure against

tampering;

(ii) maximize the probability of survival and recovery of the finalrecorded data after any incident;

(till) be of a highly visible colour and marked with retro-reflectivematerials; and

(iv) be fitted with an appropriate device to aid location.

(v) the design and construction, which should be in accordance with therequirements of resolution A.694 (17) and international standardsacceptable to the Organization, should take special account of therequirements for data security and continuity of operation.

SAQ 3

(a) What is the similarity between the Black box and the VDR?

System Options

ate an tme u er or er/responseShip's position Engine order/responsespeed Hull openisplaretertight doomHeading and fire ,ofS statusDepth Accelerations and hull stressesMain alarms Wind speed/ direction

icroph,ones

1 with 3 line feeds!

r


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22

Navigational System

and Equipment

22

(b) Enumerate the capabilities of the VDR besides data recording as perregulations.

(c) What data should be recorded additionally if improvements are to be madein cargo handling systems in a crude oil tanker?

1.11.6 Data Selection and Security

(a) The minimum selections of data items to be recorded by the VDR arespecified below. Optionally, additional items may be recorded if therequirements for the recording and storage of the specified selections are

not compromised.

(b) The equipment should be so designed that, as far as is practical, it is notpossible to tamper with the selection of data being input to the equipment,

the data itself nor that which has already been recorded. Any attempt to

interfere with the integrity of the data or the recording should be recorded.

(c) The recording method should be such that each item of the recorded data ischecked for integrity and an alarm given if a non-correctable error is detected.

Playback equipment is not normally installed on a ship and is not regarded as

part of a VDR for the purposes of these performance standards.(d) To ensure that the VDR continues to record events during an incident, it

should be capable of operating from the ship's emergency source of

electrical power.

(e) If the ship's emergency source of electrical power supply fails. the VDRshould continue to record Bridge Audio from a dedicated reserve source of

power for a period of 2 h. At the end of this 2 h period all recording should

cease automatically.

(f) Recording should be continuous unless interrupted briefly. The time forwhich all stored data items are retained should be at least 12 h. Data items

which are older than this may be overwritten with new data.

1.11.7 Performance Tests

The VDR system, including all sensors, shall be subjected to an annual performance test.

The test shall be conducted by an approved testing or servicing facility to verify the

accuracy, duration and recoverability of the recorded data. In addition, tests and inspections

shall be conducted to determine the serviceability of all protective enclosures and devices

fitted to aid location. A copy of the certificate of compliance issued by the testing facility,

stating the date of compliance and the applicable performance standards, shall be retained on

board the ship.

Onboard inspection of equipment shall ensure that batteries, enclosures and location aids

are in good condition and operational. This should be undertaken in accordance with the

manufacturer's instructions by suitably qualified/experienced personnel. Successfulcompletion of the maintenance routine should be recorded in the ship's onboard planned

maintenance log.

VDRs have a 12 hour recording capability to cover operational period when majority of

sensors will be operational, e.g., arrival, disembarkation, embarkation and departure of a ro-

ro ferry. Download of this recorded data or exchange of recording medium should be tested

and the record of these tests shall be maintained.

1.11.8 Process of Dealing with Data

In all circumstances and at all times the ship owner will own the VDR andits data. However. in the event of an accident the following guidelines

would apply. Recovery of the V DR is conditional on the accessibility of the VDR or the

data contained therein. In the case of a non-catastrophic accident, recovery of

the memory should be straightforward by removal of a hard disc from the


22/87

Automatic IdentificationSystemVDR unit to be done soon after the accident to best preserve the relevant

evidence for use by both the investigator and the ship owner. The owner

must be responsible, through its on-board standing orders, for ensuring the

timely preservation of this evidence in this circumstance.

Recovery in the case of abandonment of a vessel during an emergency,masters should, where time and other responsibilities permit, recover the

memory and remove it to a place of safety and preserve it until it can be

passed to the investigator.

Recovery in the case of a catastrophic accident, where the VDR is

inaccessible and the data has not been retrieved prior to abandonment; a

decision will need to be taken by the Flag State in co-operation with any

other substantially interested States on the viability and cost of recovering

the VDR balanced against the potential use of the information.

In all circumstances during the course of an investigation theinvestigator should have custody of the original VDR data, perhaps in the

form of the whole or part(s) of the VDR itself, in the same way as if I e has

custody of other records or evidence under the Code for the Investig tion of

Marine Casualties and Incidents.

In all circumstances the responsibility to arrange down loading and read-out of the data from the recovered memory in whatever form should, in the

first instance, be undertaken by the investigator who should keep the ship

owner fully informed. Additionally, especially in the case of a

catastrophic accident where the memory may have sustained damage, the

assistance of specialist expertise may be required to ensure the best chance of

success.

Although the investigator will have custody of the original VDR memoryin whatever form for the duration of the investigation, a copy of the data must

be provided to the ship owner at an early stage in all circumstances. Further

access to the data will be governed by the applicable domestic legislation of

the flag state, coastal state and the lead investigating state as appropriateand the guidelines given in the Code for the Investigation of Marine Casualties

and Incidents.

1.11.9 Data Items to be Recorded

SL No. Data Item Source

Date and time Preferably external to ship (e.g. GNSS)

2 Ship's position Electronic Positioning system

3 Speed (through water or over

ground

Ship's SDME

4 Heading Ship's compass

5 Bridge Audio One or more bridge microphones6 Communications. Audio VHF

7 Radar data post display

selection

Master radar display

8 Water depth Echo Sounder

91 Main alarms All mandatory alarms on bridge

10 Rudder order and response Steering gear & autopilot

11 Engine order and response Telegraphs. controls and thrusters

12 Hull openings status All mandatory status information displayed

on bridge

13 Watertight and fire door status All mandatory status information displayed

on bridge

14 Acceleration and hull stresses Hull stress and response monitoringequipment where fitted

15 Wind speed and direction Anemometer when fitted


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24

Navigational System

and Equipment

24

1.11.10 Simplified Voyage Data Recorders

The early regulations did not include cargo ships for carriage of VDRs, however it was

realised that such carriage shall assist in casualty investigations. The existing cargo

ships, when engaged on international voyages, would be fitted with a simplified voyage

data recorder (S-VDR). These dates are not yet agreed as the problem of interfacing on

such ships is not vet resolved. From present indication, it is probable that all cargo ships of

more than 3000 gross tonnage shall be required to carry such equipment.

Most requirements of the VDR and the simplified VDR are common except that the data

to be recorded.

Items to be recorded are similar to those detailed in table above except that SVDR need

not have the capability to record the following:

Water depth

Main alarms

Rudder order and response

Engine order and response

Hull openings status

Watertight and fire door status

Acceleration and hull stresses

Wind speed and direction

If it is impossible to obtain radar data then AIS target data should berecorded as a source of information regarding other ships. If radar data is

recorded, AIS information may be recorded additionally as a beneficial

secondary source of information on both other and own ship.

Any additional data items listed in the table above should be recordedwhen the data is available in accordance with the international digital interface

standards using approved sentence formatters.

SAQ 4

(a) How is the data recoded secured?

(b) What maximum period would the data be available? What happens to therecorder after this period is over?

(c) How are OOWs expected to ensure the satisfactory working of the VDR?

1.12 SUMMARY

This Unit explains the AIS as a navigational aid for transmitting and receiving information

on ships and objects in the vicinity so that the navigator is not only aware for its existence

but also the parameters such as identity course, speed and positions. In addition it has

capacity to transmit information essential to ports such as cargo, draft etc. The Unit also

explains its limitation particularly that all ships may not be equipped with the system or it

may have been switched off and as such total reliance should not be placed on the AIS.

The modulein

its second part gives details of the Voyage Data recorder which is to begive

on board as a SOLAS requirement on ships of more that 3000 gross tonnage and


24/87

Automatic IdentificationSystempassenger ships and tankers and other such ships. The VDR is self recording machine and

though strictly not a navaid, it provides a record of navigational aspects performed by the

ship. The date can be useful as an assessment of performance of the ship or for

investigation into casualties.

1.13 ANSWERS TO SAQs

SAQ I

(a) Receive information, including the ship's identity, - type, position, course,speed, navigational status and other safety-related information,- and receive

automatically similar information from other ships or stations. In the initial

stage, a number of ships may not be fitted with AIS or many of them may not

send correct information. Hence a double check is necessary.

(b) AIS operates primarily on two dedicated VHF channels (AIS I - 161,975MHz and AIS -162,025 MHz). Where these channels are not available

regionally, the AIS is capable of automatically switching to alternate

designated channels.

(c) The equipment is connected to gyro, log. GPS and to radar and to ECDISwhere available. The information, therefore, shall be updated automatically butif there is a failure in any one, the OOW may have to update the information

manually.

(d) The AIS is connected to the communication system so that it could be used asa long range system. The system is not automatic and the shore station

has to request the ship for the same. Informatively it is not mandatory either.

SAQ 2

(a) The system would be very useful in position fixing if shore beacons had theAIS transmitters and is useful in coll

ision avoidance provided all ships send

correct information. However, presently the equipment is new and a numberof users are not aware ofhow to use it. The system. therefore, should not be

totally relied on for collision avoidance or position fixing. Another

disadvantage is that the information so transmitted could be used by pirates or

terrorists also.

(b) Static information is the permanent information of the ship such as name,number, etc. and the dynamic information is course speed position, etc.

which changes and needs updating automatically.

(c) Future applications shall include :

SAR application the SAR centres shall be in a position to

direct the rescue crafts more effectively.

As it shall be possible to know the position of all the ships in thearea a local traffic controller may be able to direct traffic more.

If lighthouses or buoys are fitted with AIS it may be possible to usethem as beacons to fix positions.

SAQ 3

(a) Black box is the data recorder in the aviation industry and is so calledbecause of its colour. It records data relating to the operation of an aircraft

while in flight.

(b) Provided the additional recording systems are included the capabilities ofthe VDR include :

Provision of evidence relating to ISM compliance.25


25/87

26

Navigational System

and EquipmentImprovement in operational efficiency where data relating to these

parameters are recorded.

Investigation of accidents is not meant for setting the blame but to findout how not to let similar accident happen again. If this no blame culture

were followed, every investigation would improve safety.

Internationally there is a need to investigate accidents that happen to

foreign ships in National waters. Getting data becomes difficult.

However, if the VDR data is secured such investigation can then be

conducted smoothly.

In port state control, proving compliance becomes difficult and theautomatically recorded evidence would be a boon.

To be used as a management tool. Every ship manager would like toknow how to improve the running of his ship. Present records do not

provide adequate means of analysis and control but the VDR may just

do that.

(c) Cargo parameters shall include the initial cargo plan the rate of pumping,

back pressures, ullages recorded automatically, status of the valves, times

when each tank completed. Gas pressures in the tanks, details of de-

ballasting operations, etc.

SAQ 4

(a) The equipment does not allow any tampering. It is possible to remove thehard disc and take it ashore in case of abandonment of the ship. In a float free

VDR there is no need to this either. The data can be recovered only by the

authorised persons even though the ownership of the data lies with the ship

owner.

(b) The VDR is to record the specified data for a minimum periods of 12 hours.The equipment starts to re-record the data so that any one time there is a

twelve hours recording available.

(c) 0OWs are to ensure that the power supply is in order and where there is afailure that the emergency supply comes on line immediately. Normally, the

OOW is not required to decide anything else.


26/87

UNIT 2 SPEED MEASUREMENT AT SHIP

Structure

2.1 Introduction

Objectives

2.2 History of Speed Measuring Instruments on Ships

2.2.1 The Dutchmen's Log

2.2.2 The Common Log or Ship's Log

2.2.3 The taffrall Log

2.2.4 A Tachometer

2.2.5 The Impeller Log

2.2.6 The Patent Log

2.2.7 The Pilot Log

2.2.8 The Electromagnetic Log

2.2.9 The Ideal Log

2.2.10 Doppler Effect and Its Use in Logs

2.3 Summary

2.4 Answers to SAQ's

2.1 INTRODUCTION

In order to monitor the navigation of your ship you need to know your position, the

speed and the direction of your progress. We will now see how navigators at sea

determine the speed.

The necessity of knowing the speed and distance covered by the vessel needs no emphasis.

It should suffice to say that like any driver of a vehicle or train, pilot of a helicopter or

aircraft, a navigator would certainly like to know, at all times, what speed his vessel is

doing and what is the distance covered from last known position. Rather, it is all the moreimportant to him. The peculiar situation of navigating at sea is that with no visual

reference points available, the navigafor needs to know the speed as accurately as possible.

In spite of tremendous advancement in the field of science and technology and in the age of

star wars, nuclear armaments, Antarctica expeditions and super computers; there are still a

large number of ships sailing all over the world with no primary means of knowing the

speed. The navigators on these ships are still expected to use and rely on Patent Log,

(comparatively simple instrument) for measuring speed, knowing fully well that better

systems are available. This problem becomes all the more acute as today's masters are

required to handle modern and larger ships, in confined waters and in heavy traffic density

areas.

[Note : Before we go any further, let us be clear that the patent log as speed and distance

measurement instrument was used when no better systems were available. It records

the speed and distance with some limitations.]

Objectives

After studying this unit, you should be able to explain

dutchmen's log,

common log,

taffrail log.

tachometer.

impeller log,27


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Navigational System

and Equipment

28

patent log,

pilot log,

EM log,

ideal log,

doppler log and principle.

transducer errors,

effects of ship conditions and ship motions, and

calibration of logs.

2.2 HISTORY OF SPEED MEASURING

INSTRUMENTS ON SHIPS

Probably the earliest known attempt to estimate distance was made by the Romans, who

used a type of waterwheel. The wheel fixed to the hull, carried a drum, filled with

pebbles. Every time the wheel revolved, one pebble fell out into a tally box. By counting

the number of pebbles in the box, an estimate of distance travelled could be obtained.

Let us read the above paragraph again. Understand and try to imagine the system. Now

make an outline diagram of this device showing various parts. Can you indicate the

limitations of such a system'?

2.2.1 The Dutchmen's Log

This log was in use since 15th Century. The system used a small float thrown as far

ahead of the ship as possible and timed accurately between two points on the ship with

known distance between them, to determine the speed. The success of results depended

on the accuracy of observation and timing.

So now, you know the limitations of this type of log. It could only be used on very slow

ships of earlier era.Try this and Record the Process and the Results

When you are at anchor with a strong current running, try the above experiment on

your ship (with chief officer's permission, of course!). The two reference points need

not be bow and stern. It would be preferable to select them along parallel body, so that

signals for starting and stopping the stopwatch could he heard. Carry out this

experiment again as the tide is slacking and note the difference.

2.2.2 The Common Log or Ship's Log

This was invented in 1758 and consisted of a piece of wood (also known as chip or log).

The log or chip was allowed to drag in the water behind the ship attached with a line. The

line was wound up on a reel. The log caused the line to unreel as the ship moved. The line

was marked with pieces of cord, each having specified number ofknots in it. The distance

between the markings was 47 feet 3 inches each. The line was allowed to run out for 28

seconds. (28 seconds was the time needed then by the hour glass to empty?) The ratio of

one-hour (3600 seconds) to28 seconds is the same as 6080 ft. to

47 feet 3 inches. Thus if the log pulled 47 feet 3 inches in 28 seconds: it would pull 6080 ft.

in one hour, i.e. the speed is 6080 ft/hour or 1 nautical mile/hour or I Knot. If the log pulled

the linein

28 seconds up to the two-knot marking, the speed would be 2 knots and so on.

Even fraction of knots could be estimated by measuring the distance to the nearest knots.

Do You Know?

If the nautical mile = 6080 feet and the duration of the hourglass is 30 seconds

what should be the distance between the marks?


28/87

Speed Measurementat Ship

2.2.3 The Taffrail Log

it was fitted to the rail in the stem called taffrail and hence it was called the taffrail log. This

works on the principle of flow of water past a rotator with spiral fins that causes it to turn

as the ship pulls it through water. The rotator when connected to a recording device shows

the revolutions of the rotator and, therefore, the distance travelled. A sailor needed to make

two readings, with a known interval of time between them, to obtain the speed of the ship.

2.2 .4 A Tachometer

This is used for determining the revolution per minute (rpm) of a ship's propeller. It isalso used to determine the speed and distance travelled by ship. Knowing the pitch of the

propeller (distance travelled in one revolution) and multiplying it by rpm, the speed of

the ship can be determined and the distance covered can be worked out. However, the

accuracy of this method is greatly affected by weather, by the displacement, trim or by

the growth of seaweed or barnacles on the underwater portion of the ship's plates.

Use this method on your ship, calculate the speed and compare with your ship's log.

2.2.5 The Impeller Log

This log works on the principle of flow of water, which rotates an impeller, situated at

the base of a log tube. The impeller in turn rotates a magnet fitted at the base of a coilgenerating a proportional voltage. An electronic computer unit feeds an indicator

showing speed and distance.

2.2.6 The Patent Log

The Walker cherub Log developed in 1879 by Thomas Ferdinand Walker was probably the

most useful and long serving often it had the hourly and accumulated miles recorded

This commonly

as well. Ths Walker patent log was very commonly used. Later on, the readings were

electrically transferred to the bridge. The walker log was reliable providing you had a bit of

speed; otherwise, it was useless. This log tows a streamlined gunmetal rotator having four

pitched fins by means of a logline having a wire heart. The rotator revolves at a speed

proportional to the speed of the ship through the water and induces a constant twist

into the line. The line is connected to the register, which dissipates the twist and converts

the number of rotations into nautical miles, indicatedon

the dial of the register as well as

the speed on a remote gauge. The usual causes of error are either the rotator is damaged, the

line is of incorrect length, or that the rotator is towedin

the slipstream of the propeller.

Taking in the log line at the end of the voyage required good seamanship. The line had to be

disconnected from the register and then released back in the water so that it could unwind

itself.

2 .2.7 The Pilot Log

This operates on the pressure principle, and the pressure element protrudes through the

bottom of the ship. Increase in speed was measured as increase in pressure. The main

problems with any bottom log are:

(a) Mechanical damage to the log tube assembly occurs due to the vesselrolling or pitching heavily in a seaway or in shallow waters or when

dry-docking.

(b) Silt may be forced into the log tube to such an extent that the pressure inletbecomes choked.

(c) Physical gmis-handlin of the tube itself, i.e. withdrawing it into the hullmis -hand l ing

with possibility while flooding.

(d) Neglect of maintenance of the device used for converting water pressure

into speed and distance.

(e) Lack of calibration.

29 -


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30

Navigational System

and Equipment2.2.8 The Electromagnetic Log

This is based on the induction principle. A coil in the sensor protruding under the keel is

supplied with an alternating current. The sensing electrodes on the outer side of the sensor

measure the voltage difference generated in the surrounding water by induction due to

current in the coil and movement of the sensor with respect to the water. This voltage

difference is proportional to the speed of the ship and thus indicated. Theintegrated

values of

the speed give the distance covered.

All of the logs seen by us have some limitations. What should be then being the ideal

log?

2.2.9 The Ideal Log

The ideal log should have the following characteristics:

(a) Accurate determination of speed of the vessel ahead as well as astern.

(b) Speed should be measured with respect to the ground at all times and notwith respect to water as in the case of other logs.

(c) Versatile equipment sensitive to indicate instantaneously any changes in thespeed up to 0.01 knots and to cover all possible ranges of speed.

(d) Unaffected by weather conditions.

(e) Unaffected by Heaving, Rolling & pitching motion of the ship.

(f) Unaffected by ship conditions such as List, Trim, Hog and Sag etc.

(g) Unaffected by aeration.

(h) No moving parts and problems associated with bottom logs as listed above.

(i) Accurate determination of athwartship drifts in terms of angle of drift at seaand in channels etc.

Athwartship speed both forward as well as aft needed while docking,mooring to Single Point Mooring buoy etc.

(k) Digital, easy to read.

(1) Precise distance covered information for dead reckoning, survey purposes

and for monitoring engine performance.

(m) To facilitate keeping of anchor watches and to warn if the anchor isdragging.

(n) Easy calibration at the time of installation.

(o) Compatible with other navigation and other equipment where speed is needed

to be fed, viz : True Motion Radar, SatNav, ARPA, Gyro, Electronic chart andOil Discharge Monitoring and Control System (ODMCS) etc.

(p) Should be ergonomically designed to enable immediate and precise reading.

Doppler log is an attempt to cater for the requirements of an ideal log as listed above and

fulfils all of them except item (h) and partially item (b). However, as regards item (b) it

provides speed over ground in all shallower water (only up to 200 metres depth) where it

matters the most. It operates on the principle of Doppler Frequency shift in the sound waves

transmitted from the transducers fitted under the keel due to vessel speed.

2.2.10 Doppler Effect and Its Use in Logs

In 1842 in Vienna, Doppler pointed out that a star moving towards an observer had adifferent colour than when moving away. Since colours are associated with wavelengths of

frequencies, it implies that the frequency of light is different on two occasions; hence thename "Doppler effect or Doppler frequency shift".


30/87

Speed Measurement

at ShipBuys Ballot proved experimentally in 1843 that sound is heard to have a higher

frequency when its source is approaching the observer than when the source is

stationary. The same can be observed when a whistling train crosses a station or a fire

brigade engine passes on the road.

This change in frequency is dependent upon the relative velocity of approach. (Higher

when either source is moving towards observer, or observer is moving owards the

source or both are moving towards each other and lower when either source is moving away

from the observer, or observer is moving away from the source or both are moving away

from each other.)

It can be inferred from above that if the difference between the transmitted and received

frequencies were measured, the velocity of approach can be calculated..

Principle of Doppler Log

In Doppler log, the transducer at the bottom of the ship transmits sound waves which

are reflected by the sea bed and received by the receiving; transducer. However as

neither the ship is moving towards or away from the

sea bed nor the sea bed is

moving towards or away from the ship, the relative velocity of approach is zero and

thereby no Doppler frequency shift. To overcomethis problem, the signal is

transmitted from the transducer along the fore and aft 'ine at an angle of

approximately 60' to the keel of the vessel. This creates an apparent component ofvessels speed equal to (V cos 60) towards seabed, thus causing Doppler shift.

This increase in frequency, if measured, will provide ship's fore and aft speed.

However, it is electronically difficult to find the difference between transmitted and

received frequencies. This problem is overcome by installing two transducers, one

forward and one aft, "looking" away from each other, i.e. the forward one directing

the beam along the forward direction and the aft one transmitting along the aft

direction at the same angle to the keel. This arrangement is known as "Janus

configuration" in the name of Greek God Janus who is believed to have had two

faces pointing in opposite directions so that he could tell everything about the past

and the future.

Janus the Greek God

Assuming the vessel moving ahead, the frequency received after reflection from the

sea bed at the aft transducer will be less than the transmitted frequency by the same

amount as the received frequency is higher than the transmitted frequency at the

forward transducer. The difference between the two received frequencies, i.e. one

received forward and the one received aft can easily be measuredelectronically by mixing the two frequencies in a beat frequency oscillator

(B.F.O.) counting the resultant beats and determining the beat frequency.

The speed of the vessel in the fore and aft direction can now be computed from the

beat frequency. It may be noted that this speed is with respect to seabed or so to say

"speed over ground".

Speed over Water

Generally, Doppler log can receive echoers from seabed only up to depths of

200 mor so. However, beyond these depths a weaker echo is available from a

layer between 10 to 30 metres below the keel. The speed of the vessel can be

determined as earlier but in this case 4 wil l be w.r.t this layer and not w.r.t ground.This is called "speed over water" similar to that obtained from other types of logs

mentioned earlier. In this case, the -effect of current has to be allowed for to get the

speed made good but the reflections from a layer deep down eliminates the effect31


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Navigational System

and Equipmentof disturbances caused by the vessel itself and the effect of surface currents caused

by wind and wave motion.

Athwartship Speed

The unique feature of the Doppler log is to provide athwartship speed over

ground, which was never possible by any other logs. To measure the athwartship

speed, a similar Janus configuration is employed on port and Stbd. side amidships,

transmitting outward athwartships. Difference is measured between frequencies

received at port and Stbd. transducers and athwartship speed determined in the usual

manner.

On a larger vessel, additional information is required particularly while docking,

in the form of athwartship speed both forward and aft. In that case athwartship

Janus, configurations are mounted forward as well as aft.

Transducer Errors

Transducer Orientation Error

If the transducers are not aligned properly with the vessel's keel or with the

vessel's fore and aft line, there will be an error in the speed indicated.

Oscillator Error

If the frequency generated by the local oscillator is not exactly the one usedfor computation or not constant, the speed indicated would be in error.

Beat Frequency Oscillator(b.f. o)Error

Measurement of accurate frequency difference by Beat Frequency

Oscillator is prerequisite to speed determination. Any error will directly

affect the speed indicated.

Side Lobe Error

If side lobe reception dominates over main beam reception, the indicated

speed will be lower than the actual speed. Latest design of transducers

largely eliminates this error.

Velocity of Sound Error

Doppler log is affected by the error in speed of sound waves through the water

similar to an echo sounder. This in turn depends on the temperature of

seawater, and to a lesser degree, on the salinity and the water pressure (thus

neglected). To compensate the error due to temperature, a thennistor or

velocimeter is mounted near the transducers and deviations of the speed of

sound through water from the standard value are fed to the system

computer.

Modern design of transducers and transmitting system compensate for any

error due to transducer orientation, oscillator frequency and speed ofpropagation of sound waves due to salinity, temperature or the effect of

water pressure.

Effect of Various Ship Conditions and Ship Motions

Effect of Heaving

It can be mathematically shown that any heaving of the vessel will have no

effect on the fore and aft or athwartship speed indicated by Doppler log as the

Janus configuration cancels out the effect on individual transducers.

Effect of Trim

It can be derived that the trim of the vessel does not substantially affect thefore and aft speed and has no effect on athwartship speed as both the

transducers go up by the same amount, e.g. typically for a trim of 1.5% of


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rl ry

the length of the vessel, a speed of 15 knots will be indicated as 15.00 1689

knots.

Effect of PitchingThe effect -Of pitching is similar a vessel with Arim changing continuously .It

has no effect on athwartship speed as both transducers keep going up and;u

dawn amp for long vessel pitching p5m

"down, a fore& aft speed of will be d as oscillatingindicate

between 15.005 knots and 14.995 knots.Effectof List

No effect on the fore and aft speed of the vessel. Athwartship speed isaffected in the similar manner as trim affects F & A speed. Typically for adrip

knot knots.

will be indicated 1.997 .

Effect of Rolling(')!

SpeedShip

Vll 1 f:,lNo effectonF &A speed but athwartship speed, is affected if the list ischanging to and fro. A vessel rolling, 20 on each side will have a drift of 2knots indicated as fluctuating between 1.87 knots and 2.13 knots.However, if the mean value is noted, correct drift can be ascertained.

Calibration

Doppler log must be calibrated during engine manoeuvring trials at the time ofnew delivery of the vessel. Measured mile distance during each of the runs mustbe compared with the distance covered as indicated by Doppler log on Ground

Track. The average percentage error is to be calculated and incorporated in theDoppler log equipment. This ensures virtually error free operation in service.

While the vessel is in service, Doppler log distance readings may be compared

with charted & distanced covered While on Ground Track. To ensure correct- spedd--"v~vlhdindication by patent log When Dopper log is in operational Patent log

may be the Doppler logreadings on Water Track and percentage "'

Conclusion

The introduction of Doppler log has brought about a tremendous change in theoutlook and approach. of Masters and officers at spa. Navigators never looked.4 at nor had any respect for the speed indicated byolder logs are using accuratespeed and drift indicated by Doppler to their advantage inall their manoeuvresSafety of navigation can be improved considerably if all ships were equipped with'an operational, Doppler

l o g , . J,,

A s s i g n m e n t

detail aboutthe speed m

e

asuring equipment provided your shi . While Write in pequipment ondoing this include in your explanation e o owing

a T e of e ui ment., , j, , , - , , , H , , j "Ai 1 ' ) , ( , - , ~ , ; " I ; ~ - ' - s ' l l o - I .-I d - ra j , 2 3

5 , !

he

;fit

(d) What maintenance, does it need?

and under all, Wweatheretc ?

lkr~n

b kffiiequipmenttc.t

(g) Is it connected electronically to other navigation instruments?(h) Does it provide speed in the ahead direction only?

3 3


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34

Navigational System

and Equipment(i) Does it show the speed or does the speed have to deduced from the

distance run?

Are there any corrections to be applied?

(k) What method is used on boardin

case of failure of this equipment?

It is our sincere belief that by studying the system on board not only you will be

more familiar with the equipment but also you shall educate us. Best explanation

of each of the log shall be our courseware on that system at the next revision

[Hint: Most of the information should be availab

l

e in instruction manuals.]S A Q 1

(a) Why is the knowledge of speed necessary to a navigator?

(b) In most of the older logs rotator, impellers or similar devices were used.What is the principle involved in obtaining speed using these?

(c) How would you ascertain the speed and distance by reading the tachometer?

(d) In what way is the patent log a simple instrument?

2.3 SUMMARY

Essential function of the speed log is to measure the distance the ship has steamed or sailed

and then finding the speed.This unit explains the equipment for this purpose from the very

ancient to the most modern times. The unit also explains that even in the most modern logs

there are limitations and they need to be taken into account when a ships dead reckoning

position is to be worked out. Modern logs, which use Doppler principles,In

are to date considered the most accurate.

2.4 ANSWERS TO SAQs

S A Q 1

( a ) ) Fixing the position of a ship by dead reckoning needs distance steamed

and course steered. Distance steamed can be obtained by logs.

(b) The principle of impeller is the same as the distance moved by a screw.

Knowing the pitch, it is possible to calculate the distance the impellermoves.

(c) The tachometer reads the number of revolutions of a propeller. Knowing thepitch of the propeller, it is possible to calculate the distance the propeller and,

therefore, the ship moves through the water. In such calculations, there is

possibility of a slight difference and this is called slip of the propeller.

(d) Patent log utilises no advanced technologies and needs the log line,impeller, a governor and an indicator, with three dials, one marked in

divisions of 10 up to 100 miles, the second marked in divisions of miles up

to 10 miles and the third marked in four quarters of a mile. On some ships the

reading were transferred to the bridge electrically.


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UNIT 3 RADAR FOR NAVIGATION

Structure

3.1 Introduction

Objective

3.2 Precautions to be Taken Before Starting the RadarStarting

3.3 Initial Process

3.4 Switchingon the Radar Set

3.5 Using Range Rings Accurately

3.6 Use of Bearing Cursors and Different Methods of Measuring Bearings

3.7 Use of Electronic Beari ig Cursor (EBL)

3.8 The Main Units of the Radar

3.9 Summary

3.10 Answers to SAQ's

3.1 INTRODUCTION

All of you have heard about the Radar and perhaps have seen it on your ship visits before

joining a ship, Radar in its early days, instead of being an aid to navigation to avoid

collisions. it got a bad name as radar oriented collisions. The main reason for this was

ignorance on its abilities and limitations. As you learn to operate this very valuableIequipment, try to understand this important aspect and the radar shall be your friend.

A radar unit can pierce darkness and weather conditions in which human eyesight is

obstructed. Within its range, it can show

ships, planes, storm clouds, small islands,

coastlines and prominent landmarks. It can also be used to measure the distance to anobject and the speed at which the object is moving toward or away from the observer.

Radar was developed from the work of many scientists. Discoveries made by Heinrich

Hertz, Karl F. Braun, and Christian Hulsmeyer of Germany, Guglielmo Marconi of Italy,

and Lee De Forest of the United States laid some of the foundations. Robert

Watson-Watt of Scotland patented a radar system in 1935. British and American

scientists when working together perfected radar during World War 11.

6, Marconi

Radar uses electromagnetic waves usually short-wavelength waves called microwaves.

These waves bounce back from solid objects in their path, the way sound waves bounce

back from an object and produce an echo. Scientists learned to use reflected microwaves for

detection and measurement. The name radar was coined from the first letters ofthe words

"radio detecting and ranging'. A radar set with its antenna, both transmits and receives. In

the most widely used type of system, wave bursts or pulses are spaced so that the echo

from one pulse is received before the next pulse goes out. For example, a


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Navigational System

and Equipment

36

set may be designed fora range of 93 miles. It sends out pulses at internalsof a

thousandth of a second, and these travel at a speed ofI I86,000.miles

(300,000 kilometres) per second. In a thousandth of a second, a pulse has time to travel

to the edge of the search area, strike an object and return a round trip of 186 miles (300

kilomet

Documents

IMU Navigational System and Equipment