One channel I am following and think will have more interesting content in the future is REV Ocean. This is the channel for a new 600-foot superyacht owned by Norwegian Kjell Inge Røkke. He seems to have taken the approach of being very open about the workings/use of the yacht, which I think is quite rare for vessels of this size.
Heres a really good channel where it shows really simple instructional and fact based maritime videos with some awesome animation from a guy who is currently a Harbour Master and a former cruise ship officer.
Not in the same category as most of the lifestyle channels, but I follow Pacific Yacht Systems which has loads of great content on all matters marine electrical, including playlists of full two day seminars that the owner, Jeff Cote, has run. Pacific Yacht Systems