Vessel depth (draught) is usually (or always) a static number;hard coded in the ais transponder and never again uodated and thus provides zero information. The

Vessel depth (draught) is usually (or always) a static number;hard coded in the ais transponder and never again uodated and thus provides zero information. The only somewhat reliable data are position and heading and their derivatives. Next to that you can get something out of the broadcast frequency, and that's about it. Of course the data can and is easily manipulated by some, and the broadcast is lossy so sometimes a few bits get lost or mangled in transit, there is no proper error correction in the protocol