Recommendations for Integration of AIS in Bridge Operations

1. Introduction

The recommendations expressed this paper are based on the results of a test of AIS in British Columbia and South East Alaska that was held in August and September 2000 on three cruise ships. The test and its results are detailed in the attached document.

The recommendations are the author’s and are yet to be endorsed by the organizations that sponsored the test. The recommendations are intended to be considered by members of the IMO, IALA and IEC committees that are charged with setting standards for the integration of AIS in Bridge Operations, as well as by ECDIS, ARPA radar and Integrated Bridge System manufacturers.

Readers are encouraged to comment on the recommendations by responding to:

ir Fred W. Pot
Principal
Marine Management Consulting
3837 31^st Avenue West
Seattle, WA 98199-1713
USA
206-301-9626
206-283-7108 Fax
fpot@uais.org
www.uais.org

Responses will be published along with this document on www.uais.org.

The recommendations are not separated by type of display, i.e., Radar and ECDIS, because one of the recommendations, for consistency purposes, is to display AIS information in the same manner whatever the display.

2. Display of un-selected targets

To minimize clutter on the active screen un-selected targets, be they radar or AIS, should not be labeled and should not have a vector emanating from them.

Un-selected radar targets should be represented by the echo of the target as should consolidated ARPA/AIS targets for boats smaller than 20 m LoA that have a TCPA of more than 5 minutes. The OOW should be able to select whether he/she wants to have the latter displayed as an echo or as a diamond.

Other consolidated ARPA/AIS targets should be shown as a diamond.

The color of a diamond should be commensurate with the type of ship it represents.

Again depending on the preference of the OOW, AIS targets for boats smaller than 20 m LoA that have a TCPA of more than 5 minutes should be suppressed.

Other AIS targets should be displayed as a triangle. The color of the triangle should be commensurate with the type of ship its represents. The triangle should be hollow if the EPE of the GPS on which the AIS target’s position is based is greater than 50 m or if the last AIS update is more than 3 intervals old. The interval is detemined by the speed and the rate of turn of the target

A diamond or triangle icon should be replaced with a simplified silhouette of the ship it represents as soon as the LoA of the ship to the scale of the active chart is greater than the icon. The silhouette should be aligned with the target’s heading. Its LoA and Breadth should be to scale of the active chart. The color of the silhouette should be commensurate with the type of ship it represents.

3. Display of a group of targets monitored for collision avoidance purposes

Targets to be monitored should be selectable individually and by setting a guard zone. Selected AIS and consolidated targets should be displayed in the same fashion as un-selected targets. Again, depending on the preferences of the OOW, icons for targets representing boats smaller than 20 m that have a TCPA of more than 5 minutes should be suppressed. Selected radar targets should be displayed as a circle.

The predicted path over ground should be displayed for the selected targets. The predicted path over ground should have a radius of SOG divided by the tangent of the ROT. The arc of the path should be ROT times the number of minutes the path is projected. The predicted path should be displayed to the scale of the active chart.

A maximum of 10 characters should be used to label each target. The label should default to the first 10 characters of the full name, but should be editable in the ‘Target Information Form’ (see below). ARPA targets, too should have an editable label. The font and color of the label should be different from place names used in the electronic charts. The label should automatically seek a position around the icon to avoid the predicted path line.
 
 
 
 

CPA and TCPA calculations should take into account the predicted path.

4. Collision Avoidance Form

This form should appear off the active part of the screen. The values displayed in the form should by dynamically updated. Selecting a new target should cause the values displayed in the form to represent the new target. If an ARPA target is selected then there will be many unknown values. They should remain blank. The OOW should be able to select which of the fields listed below he/she wants to see in the form. This preference should be recorded in a Display Preference Profile (See XI below).

1. Full Name spelled out
2. CPA in NM
3. TCPA in Minutes
4. Range in NM
5. Bearing in degrees
6. Course Over Ground in degrees
7. Heading in degrees
8. Rate of Turn in degrees per minute
9. Speed Over Ground in knots
10. Log Speed in knots
11. Type of ship spelled out
12. Maneuvering Restrictions (Yes or No)
13. Destination
14. Tow Configuration
15. Draft in meters
16. ‘More Target Info’ Button

5. Target Information Form

This form should replace the Collision avoidance form when the ‘More Target Info’ button is clicked on the ‘Collision Avoidance Form’. When a new target is clicked on the active screen this form should close and be replaced by the ‘Collision Avoidance Form’ for the new target.

If this information form is displayed for an ARPA target and a name has been entered in the ‘Abbreviated Name’ field, this name should be displayed in both forms as the ‘Full Vessel Name’ and should be used to label the ARPA target on the active screen. The OOW should be able to select which of the fields listed below he/she wants to see in the form. This preference should be recorded in a Display Preference Profile (See XI below).

1. Full Name spelled out
2. Abbreviated name (‘Handle’), Editable, default to full name
3. Maneuvering Restriction Comments
4. Status
5. Seconds elapsed since latest AIS Position Update
6. Estimated Position Error in meters
7. Direct or Relayed AIS Data
8. Single AIS or Consolidated with ARPA
9. Bow Crossing in NM
10. Time of Bow Crossing in Minutes
11. LoA in meters
12. Breadth in meters
13. Intended Route
14. Hazardous Materials Carried
15. MMSI
16. IMO Number
17. ETA
18. ‘Interrogate’ Button
19. ‘Back to Collision Avoidance Data’

6. Own Ship Collision Avoidance Form

This form and the following ‘Own Ship Information Form’ are intended to allow the OOW to check the information being broadcast from the own ship by its AIS transponder. It should appear off the active part of the screen when the own ship icon is selected.

1. Full Name spelled out
2. Course Over Ground in degrees
3. Heading in degrees
4. Rate of Turn in degrees per minute
5. Speed Over Ground in knots
6. Log Speed in knots
7. Type of ship spelled out
8. Maneuvering Restrictions (Yes or No)
9. Destination
10. Seconds elapsed since latest AIS Position Update Transmitted
11. Estimated Position Error in meters
12. Tow Configuration
13. Draft in meters
14. ‘More Own Ship Info’

7. Own Ship Information Form

This form should appear off the active part of the screen when the ‘More Own Ship Info’ button is clicked on the ‘Own Ship Collision Avoidance Form’.

1. Full Name spelled out
2. Own Transponder Performance
3. Primary or Back-Up Transponder used?
4. Maneuvering Restriction Comments
5. Status
6. LoA in meters
7. Breadth in meters
8. Intended Route
9. Hazardous Materials Carried
10. MMSI
11. IMO Number
12. ETA
13. ‘Back to Collision Avoidance Data’

8. Traffic Control Display

While AIS was designed to be used by shore-based VTS operators, ship-board bridge teams should be allowed to use AIS to ‘control’ traffic in areas that are not covered by VTS particularly those with reduced visibility, narrow congested channels, sharp channel turns or around capes.

This can be achieved if ships’ transponders are set up to transmit their active route. One of the messages in the AIS standard is specifically designed for this purpose.

One way to do this, as suggested by Tracy Fleming, 3^rd Officer, SEA PRINCESS, is to allow the OOW to display the (abbreviations of the) names of ships that, according their own intended route and progress along it, are expected to arrive at or near a critical ‘Gate’ at about the same time, say plus or minus 30 minutes, as the own ship. The ‘Gate Passing Sequence List’ should be displayed off the active part of the screen and be valid for any selected ‘Gate-waypoint’ of the own ship’s active route. The list should be sorted by ETA at the ‘Gate-waypoint’ and show what that ETA is. The form could simply represent a snapshot of the expected traffic situation at the ‘Gate-waypoint’ although a ‘Refresh’ button should be provided.

This list should allow the bridge team to contact the ships via VHF that it expects to encounter near the ‘Gate-waypoint’ to coordinate passing arrangements. It would probably not be easy nor necessary to have the system figure out from which side other ships will approach the ‘Gate’. It should, however, be possible to attach a field that shows the Gate passing direction (i.e., ‘Southbound’ or ‘Inbound’) to each AIS target. The content of this field should be visible in the ‘Gate Passing Sequence List’ and editing this field should be point-and-click rather than require typing.

AIS Targets that do not broadcast their intended route as well as ARPA targets should be included in the ‘Gate Passing Sequence List’ if they could reach the ‘Gate-waypoint’ at about the same time, irrespective of their current course. The ETA of such targets at the ‘Gate-waypoint’ should be based on their range to the ‘Gate-waypoint’ divided by their current speed. The ETA of such targets should be editable, so that they can be updated after contacting ARPA target ships via VHF.

This is an important application of AIS because it will allow the OOW to plan and control a traffic situation rather than be forced to react to it.

9. Broadcast of fixed and voyage particulars

The interval between transmissions of fixed and voyage particulars should not be set at 6 minutes, regardless of the speed of a ship, as is called for in the AIS standard. Faster ships should broadcast these details more frequently. The broadcast interval in minutes should be 100 divided by the vessel speed in knots.

While the above will identify fast ships to slower ones in a more timely fashion, it won’t do so the other way. For this reason and to allow the OOW to identify a new AIS target as soon as it appears, rather than wait, he/she should be able to request a target to broadcast its fixed and voyage data by clicking on an ‘Interrogate’ button in a target’s information form.

10. Target consolidation

An ARPA and an AIS target should be consolidated if all following conditions are met simultaneously:

1. The difference between their ranges is within 2.5 % of the average range
2. The difference between their bearings is less than 3 degrees
3. The difference between their relative speeds is equal or less than .2 knots
4. The difference between their relative courses is less than 10 degrees
5. AIS target position updates are being received with an interval commensurate with its speed and rate of turn
6. Conditions A. through E. above are met for three consecutive AIS position updates

Obviously the validity of these criteria needs to be verified in tests.

A target’s relative speed and course should be considered rather than their over ground equivalent to eliminate the effect the error in own ship position would have on ARPA’s calculation of over ground values.

If target consolidation conditions are met, then the consolidated target should be positioned on the bearing line between the AIS and the ARPA target at a range from the AIS target equal to the Estimated Position Error. If that range is greater than the range between the AIS and the ARPA target, then the consolidated target should be positioned on the ARPA target. The COG and SOG of the target should be set to their AIS target values.

11. Display Preference Profiles

The OOW should be able to set and edit his/her own display preference in a profile document. Display Preference profiles should be listed by last name of the OOW and should set both ARPA and ECDIS display preferences.
 
 

12. Fail-Over

SOLAS ships should be required to carry dual transponders and both should be operational. If the primary transponder’s diagnostic program finds that it is not performing properly, it should automatically sound an alarm on the bridge and switch over to the back-up transponder. It is beyond the scope of this paper to spell out what should cause fail-over.