NMEA wind speed reading 50%

[Ardenfour]

Can anyone suggest a reason why my Navman wind instrument nmea output is half the reading displayed on the instrument display? It was working fine for the last 2yrs, but now the windspeed on the connected plotter and autopilot is exactly half the figure displayed on the Navman.

 

[Chiara’s slave]

A wild stab, is it a unit thing? Metres per sec on the plotter, and knots on the wind instrument? That’s very close to half.

 

[Laser310]

are the units the same?

1km/hr is pretty close to 0.5kt

 

[Ardenfour]

Good points, I'll check back at the boat. Thanks