So in the end Dagnall superbly killed the monster!
He managed to patch the nmea4 .bin file to add the magnetic heading, facing a double constraint : send heading in an NMEA sentence that Sailgrib can decode, and alleviate for a bug in Sailgrib that zeroes the present heading value if a VHW sentence with a void magnetic heading is received.
Besides, he found a way to overcome the bin upload issue I had :
https://www.vela-navega.com/forum/viewt ... f=13&t=232
Thumbs up for Dagnall and Luis !
Bruno