NMEA VHW datagram format
The NMEA VHW datagram contains the compass heading to which the vessel points, and the speed of the vessel relative to the water.
Format
$--VHW,x.x,T,x.x,M,x.x,N,x.x,K*hh<CR><LF>
Description
1 $—Talker identifier
2 VHWDatagram identifier
3 x.x,THeading (Nautical miles)
4 x.x,MHeading (Degrees (Magnetic))
5 x.x,NSpeed relative to water (knots), Resolution = 0.1 knots
6 x.x,KSpeed relative to water (km/h), Resolution = 0.1 km/h
7 *hhChecksum