There is a bunch of web based stuff you can do. Youtube was given as an example, but there is a lot else out there.
You can sell digital photos to Foap.
You can run adsense or similar on a blog
You can work for a call centre via VPN. My wife does this as an independent contractor taking take out orders on her computer. All she needs is a laptop, head set and wifi. She does it from home when the babies napping, but a cruising boat is just a floating house moving from place to place from time to time. Decent internet is a requisite for this, so cruising plans must be adjusted accordingly.
Also, some employers offer really good leave programs these days if you want the security of full time employment but also want to live on a boat and float around from place to place from time to time. Some offer unpaid leave of absences for "Personal reasons" (like going boating), up to 1 year. I think there is a limit on how many times you can take it. Another thing a lot of employers are offering these days is leave with income averaging. For example, can take up to %20 reduction in wages for a corresponding amount of extra vacation, (so that works out to 10 weeks/year plus your regular vacay, or 1 year off in 5). And there are telework agreements to be had if you want to set up a home office on your boat and work from there, although this would likely fall more into "liveaboard" status then the traditional idea of "cruising". My employer offers variations on all of the above programs (in addition to the 18 months parental leave for birth of a child I mentioned earlier).
Some academic and clergy type positions also have pretty good sabbatical programs as well.
There are many options for boat living and exploring. I have tried out a few. Waiting until retirement and living off investment or pension is the most popular, but there are lots of people who dont follow that kind of traditional approach and just kind of do there own thing. Labels applied by others are pretty easy to shrug off when you are out on your boat having an adventure to some new place on a Wednesday afternoon