DVD or video
IMHO, there will still be a demand for VHS. If you only produce the program in DVD, you will lose whatever market there is for VHS. My local public library loans movies in both DVD and VHS format, but there are far more in VHS format, and they seem to get more play than DVD. I live in a midwestern metropolitan area with well over a million people. Other cities may be transitioning to DVD much faster, but I think there is still a significant VHS market. Can you produce a test issue of a couple thousand in each format, and then order a larger quantity based on the percentages sold of each?
Good luck! I started sailing at about the same time you started writing, and have always enjoyed the accounts of your travels.