The Waterways Management message can be used to facilitate vessel traffic movement in confined waters. More “directive” than advisory, this message can be broadcast (e.g., information for all ships or a group of ships) or addressed (e.g., information/direction to a single ship). Examples include: lock, gate, narrows, or single passage area.
There are three sub-types of this message;
1) for providing a position/name of the waterway feature,
2) for providing a list of vessels and their sequence order/times, and
3) to specify a name (or IMO number) for a vessel with unknown MMSI.

Specific information for each vessel includes: sequence time, direction, and vessel MMSI. The complete list of message types is contained in Table 1.

• The message can be broadcast or addressed, depending on which alternative is more appropriate.
• If message sub-type 0 is used, then a message sub-type 1 must also be sent to define the position for the sub-type 0 sequence. The message sub-type 1 can be transmitted less frequently than the sub-type 0 if desired.
• The Message Linkage ID can be used to link additional text (e.g., a separate Linked Text message). However, the same source MMSI needs to be included in both the Waterways Management and the Linked Text message.
• If there are no vessels in the queue then the MMSI of 0000000000 can be used for the first vessel with the time being the time of the data report.
• If the MMSI of the vessel is unknown then an MMSI of 1000000003-1000001023 can be used. The name or other identifier of the vessel is then transmitted in a subpart 2 message with the same number 3 – 1023 used to link the vessel name with the position in the queue. These numbers will be used sequentially by the competent authority transmitting the lock queue and then re-used once the range is exhausted. A range of 1020 numbers should be more than sufficient so that by the time the numbers are reused there is no confusion.
• All of these special “MMSIs” are 10digit numbers so as not to be confused with real MMSIs.
• Subtype 2’s sent as needed along with the subtype 0’s to specify name or number for vessels with unknown MMSI. Anywhere from 0 to 7 subtype 2’s sent with each subtype 1 message.
• New subtype 2 messages should be generated each time the vessel list is updated (subtype 0 message).
• A message version number is encoded as part of the message; if the received version number is different than what the display system has been programmed for, the data should be ignored.
• Positions are in WGS 84 Datum.
• Typical transmission sequence would be subtype 1 message at a longer interval (10min perhaps) and then subtype 0 and 2 at a shorter interval (perhaps 3 min).
• The display system should remove the WWM message from the display 60 minutes after the time of the last vessel in the list unless a removal message is received sooner.