In 1997, in university, I attempted to switch completely to Linux. For the most part, it succeeded, but not 100%. I was able to do about 90% of what I needed to do.
Fast forward, working for a tech-forward company, I attempted to switch completely to Linux. Again, there were a few critical components that I couldn't get around, the corporations time logging system; Microsoft project management software; Microsoft Visual Basic.
For the past two years, I have attempted to go Microsoft-free again and am quite happy. The limitations are
1) Standard business software that is only available on the Windows platform. I doubt you are making project plans or drawing Visio diagrams on the boat so you may be ok.
2) Video games. You simply can't get mainstream video games to work well in the Linux world; Yes, you can play some of them, but they never work as well.
At home, my Ubuntu server runs; my firewall, e-mail server, web server, company's phone system, allows vpn access, remote proxy access, my entertainment system including HD movies, TV, music center all through my TV. I can connect and control all of the above via my blackberry from anywhere I have signal. (All of which has run for more than 258 days without a glitch... including updates!)
On my laptop, it runs all of my daily use software - including OpenCPN - including browsers, Office suite, e-mail, PDF's, etc.
The question doesn't come down to "What can't Linux do?", we must necessarily ask, "What can't the user do?" And there's the rub. I'm technical and can make it spin on its head but what can you make it do? If something goes wrong, who are you going to call to get advice? In the hands of a regular user, Microsoft Windows will inevitably fail and the response will be to swear at Microsoft and then go pay some pimply faced 14 year old to fix the issue. With Linux, it doesn't generally fail but the user generally makes a mistake which requires some know-how to get things back to the way they were... that "know-how" is hard to find if you can't do it yourself.
So... are you more willing to roll-up your sleeves and get technical? Or are you more apt to pull out your wallet and have someone else fix the issues?
Hmmm... it appears I'm more verbose than I intended to be. Feel free to msg if you get stuck.
(PS, CM93 charts work in OpenCPN...)