A vessel’s draught relates to how deep the vessel sits in the water and is important for safe navigation. Draught gauges are often painted on the side of a vessel and commonly sensors are used for monitoring the draught. These sensors do not automatically update AIS draught.

The International Maritime Organisation (IMO) guidelines advise a vessel’s crew to manually input the vessel’s draught, as AIS voyage information, at the start of the voyage, using the maximum draught for the voyage. They recommend that this should be amended as required and draught may be updated at the same time destination and ETA are updated.

AIS reported draught is voluntary and because it is manually entered it may be missing or incorrect for vessels.

Draught changes may indicate a change in cargo, ballast water, or fuel and tend to occur near port, when vessels meet, or when voyage destination and ETA are being updated.

Analysing draught changes may provide further supporting evidence of an inferred transshipment, where only the fish carrier vessel is visible on AIS or of a port call where a vessel has missing AIS.

Try it out: See a fish carrier’s increase in draught immediately after an inferred transshipment. Tip, changing the Filter & sort to display the track history as time is useful when analysing detailed vessel events.