Parameter

# of bits

Description

Standard Message Header

Message ID

6

Identifier for Message 8; always 8.

Repeat Indicator

2

Used by the repeater to indicate how many times a message has been repeated. (See ITU-R M.1371-3, Annex 2, § 4.6.1).

0 – 3; 0 = default; 3 = do not repeat any more. Set to 0 (default).

Source MMSI

30

MMSI number of source station. This varies according to the transmitter ID.

Spare

2

Not to be used. Set to zero.

Binary Data

Designated Area Code

10

Designated area code (DAC). (See Rec. ITU-R M.1371-3 § 2.1, Annex 5). Set to 367 (US).

Function Identifier

6

Function identifier. Set to 23.

Application Data

Version

3

Sequential number used to indicate the message version in steps of 1.

0 = test message = default; 1 – 7 = message version.

Set to 0.

UTC day

5

UTC day of the time of the data.

1 – 31; 0 = UTC day not available = default.

UTC hour

5

UTC hour of the time of the data.

0 – 23; 24 = UTC hour not available = default;
25 - 31 (reserved for future use).

UTC minute

6

UTC minute of the time of the data.

0 – 59; 60 = UTC minute not available = default;
61 - 63 (reserved for future use).

Longitude

25

Longitude of the data in 1/1,000 minute (±180°) in WGS-84 datum.
East = positive, West = negative (as per 2’s complement);

181° = not available = default.

Latitude

24

Latitude of the data in 1/1,000 minute (±90°) in WGS-84 datum.
North = positive, South = negative (as per 2’s complement);

91° = not available = default.

Air Pressure

9

Air pressure, defined as pressure reduced to sea level, in 1 hPa increments.

0 = pressure <800 hPa; 1 - 401 = 800 – 1200 hPa;
402 = pressure of 1201 hPa or greater;
403  = data unavailable = default;
404-510 = reserved; 511 = not to be used.

Air Temperature

11

Dry bulb temperature in degrees Celsius, in 0.1 degree steps.

-60.0 to +60.0 degrees Celsius(as per 2’s complement);
-1024 = data unavailable = default;
-1023 to -601 = reserved;
601 – 1023 = reserved.

Wind Speed

7

Average of wind speed values over the last 10 minutes in 1 knot increments.

0 - 120 knots; 121 = wind 121 knots or greater; 122 = data unavailable = default; 123 – 126 = reserved; 127 = not to be used.

Wind Gust

7

Max wind speed reading during the last 10 minutes in 1 knot increments.

0 - 120 knots; 121 = wind 121 knots or greater; 122 = data unavailable = default; 123 – 126 = reserved; 127 = not to be used.

Wind Direction

9

Direction of the average wind over the last 10 minutes in 1 degree increments.

0 – 359 degrees; 360 = not available = default; 361 - 510 = reserved; 511 = not to be used.

Spare

1

Set to zero.

Total bits

168

1 slot message