Seeing two winds charts is like getting a second opinion. If there is consensus between the forecast models there is a higher degree of confidence those conditions will prevail.
The BOM and GFS models are independent. They are produced by different agencies and have different model physics so when they arrive at the same conclusion you can be more confident the forecast will be correct.
If the models differ on any given day and one says strong winds while the other says low winds then there is little consensus and therefor lower confidence in an accurate forecast on that day.
The BoM model is the model we have always used and is more accurate. GFS is the model used by most other weather sites including Windfinder, Buoyweather, Windy, WindGuru and others.
The BoM (ADFD) model has a resolution of 3km in VIC & TAS and 6km in other states, it covers Australia out to a distance of 60nm from shore. The GFS model has a resolution of 13km and covers the entire globe.
The BoM model is the best for Australia and in most cases it's predictions should be preferred over GFS.
Note: GFS exists in a few versions - 13km, 22km and 40km. The 13km version is best due to its higher resolution and this is the version Fish Ranger uses.
Wondering why we don't we use the ECMWF 9km model? The BOM model is based on the 'EC' model so they have very similar model physics and are not independent. By showing BOM and GFS models we can present two high quality independent forecasts.
We use bilinear interpolation to provide forecasts true to the chosen location.