A quick example on what $GPVBW messages are. Keep in mind that the sentence Identifier can also be displayed as $GNVBW .The message is the same but some GNSS receivers use this format.
Dual Ground / Water Speed
Water referenced and ground referenced speed data.
x.x = Longitudinal water speed, knots
x.x = Transverse water speed, knots
A = Status: Water speed, A = Data valid
x.x = Longitudinal ground speed, knots