Thanks for the response. I have now read the whole thread referenced by Cagney, not just the Polar Navy
(Brak) proposal part pointed to in the link above.
However, I am still unable to fully understand the technical problem. [As an aside, my last coding efforts were in Coral66 and Ada so I am not fully up to speed with 'modern' languages and OSs!]
Is it actually 'impossible' to develop the code to read previously loaded BSB4 charts under Linux (because proprietary encryption type data is not available) or is it just difficult/tedious to generate an SDK for BSB4 on Linux as PolarNavy have done?
BTW I would add that I am big fan of OpenCPN
and it is now the navigation
programme of choice (under Windows) on Playtime. However, like others, I am not entirely happy running such 'mission critical' software
under Windows and would be delighted if I could get my charts to load under Linux/Ubuntu!