U A I S
Universal Automatic Identification System

Pilot Carry Aboard ECS and the AIS 'Pilot' Port

When considering an ECS for carry aboard purposes please keep the following in mind:

The 'Pilot' port on a Class 'A' AIS Type Approved Transponder will provide Own Ship position, SOG and COG  information, however, it is not in the format of the regular NMEA  0183 sentences. If their sensors are connected to the AIS transponder, the pilot port will also provide Heading, ROT and Log Speed, however, again these sentences are in 6-bit encapsulated format of messages 1, 2 or 3.

Since most ECDIS and ECS determine the Own Ship information from regular NMEA messages they will continue to need to be connected to a separate GPS for Own Ship information even if they are able to display AIS information. 

ECDIS and ECS that are able to determine Own Ship information in the format of AIS (Outbound) messages 1, 2 or 3 can be used with just a single connection to the pilot port on Class 'A' AIS transponders and show Own Ship position, SOG, COG and possibly heading, ROT and Log Speed as well as AIS (target) information received through AIS. The South East Alaska Pilots Association (SEAPA) is testing ECS packages on Cruise Ships that can do this. Click here for more information about the test results and their recommendations.

The communication protocol used by the pilot port is RS422. This protocol will need to be converted to RS232 before it can be connected with the serial port of a laptop computer. PCMIA converters are available for about US$ 400. Standalone converters are also available.

A further complication is the pilot port connector itself. It is a round male Sub Miniature D9 37 socket. It is not a regular D9 serial port (see picture below). 

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The following details about the pilot port are from Ross Norsworthy of L-3 Communications who was a member of the US Delegation involved in defining the AIS Class 'A' specifications.

1.) The mating connector for the plug (the connector on the cable that the pilot is to bring aboard) is:

        AMP/Plug, Shell Size 11, 9-pin, Std. Sex 206485-1

        AMP/Socket 24-28 AWG, Crimp, Gold/Nickel (for 206485-1 Plug) 66505-4 Female

        AMP/Cable Clamp-Plastic Shell, Shell Size 11 206062-1

2.) The pin designations per IALA are:

        Pin 1, TxA

        Pin 4, TxB

        Pin 5, RxA

        Pin 6, RxB

        Pin 9, Shield (for a shielded cable)

Important Note: Tx and Rx (Transmit and Receive) are from the perspective of the AIS transponder.

 

This wiring diagram is the same but with higher resolution (PDF 150K)

In view of the above, my counsel would be to use shielded cable (overall shield) with two shielded twisted pairs (each pair individually shielded). This is an easy cable to find, where each shield has a drain wire. Hook up the shield drainwire for the portable unit's TxA and TxB pair to the portable unit's ground and don't tie it to any pin on the plug. Hook up the shield for the portable unit's RxA and RxB pair to Pin 9. Hook up the overall shield also to Pin 9. This in effect provides shielding and ground isolation with no need for C-Leads. Remember that the pin designations on the plug are referring to the AIS unit, not the portable unit. Thus, the AIS unit's TxA/TxB pair connects to the portable unit's RxA/RxB pair, and the AIS unit's RxA/RxB pair connects to the portable unit's TxA/TxB pair. Later, if and when C-Lines are designated, there will be no incompatability and no need to change the carryaboard equipment or cable. The data-rate is 38.4 KBPS, and the messages are defined.

Click here for details about the Pilot Port Design Considerations provided by Ross Norsworthy

 

 

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