Parameter Number of bits Description MessageID 6 AIS message number. Must be 8 RepeatIndicator 2 Indicated how many times a message has been repeated UserID 30 Unique ship identification number (MMSI) Spare 2 Reserved for definition by a regional authority. dac 10 Designated Area Code - 366 for the United States fid 6 Functional IDentifier - 63 month 4 Start time of most recent notice UTC month day 5 Start time of most recent notice UTC day of the month 1..31 hour 5 Start time of most recent notice UTC hours 0..23 min 6 Start time of most recent notice UTC minutes longitude 28 Center of the area/zone East West location latitude 27 Center of the area/zone North South location timetoexpire 15 Minutes from the start time until the notice expires. Max is aprox 23 days radius 14 Distance from center of detection zone (lat/lon above). Distance in increments of 10 meters areatype 8 What does this circular area represent Total bits 168 Appears to take 1 slot