I don’t think that Windy is willing disseminate GRIB files mainly because of the licence agreement with the ECMWF.
The case should be different with GFS whose GRIB files are freely accessible.
If you imagine using GFS GRIB files on OpenCPN, whether it is GRIB files sent by any application or by Windy, you would not see any difference on Open CPN as this navigation software read these files and displays the weather data with its own UI.
If you imagine the same offline rendering as on your PC on land, Windy would have to develop its own offline viewer software.