NMEA VBW datagram format
The NMEA VBW datagram contains water- and ground-referenced vessel speed data.
Format
$--VBW,x.x,z.z,A,r.r,q.q,A,p.p,A,c.c,A*hh<CR><LF>
Description
1 $—Talker identifier
2 VBWDatagram identifier
3 x.x:  Longitude water speed (knots)
4 z.z:  Transverse water speed (knots)
5 A: Transverse water speed, Status
A = The data are valid.
V = The data are not valid.
6 r.rLongitudinal ground speed (knots)
7 q.qTransverse ground speed (knots)
8 ATransverse ground speed, Status
A = The data are valid.
V = The data are not valid.
9 p.pStern transverse water speed (knots)
10 AStern transverse water speed, Status
A = The data are valid.
V = The data are not valid.
11 c.cStern transverse ground speed (knots)
12 AStern transverse ground speed, Status
A = The data are valid.
V = The data are not valid.
13 *hh: Checksum