I think there are very few jobs that can be done while cruising if you wish to keep moving, ie actively cruising.
The IT idea sounds fine but I think there are very few in our size boats actively cruising because the Internet is so iffy in many places. And the person who can spent $10,000 per month on satelite broadband would be in a bigger boat...
There are some who may be making a few spending dollars but not a reasonable portion of a budget and probably investing lots of hours.
If you are going to profit by $30,000 per year there must be clients who do Ned to see you, and have good land based system.
The yacht delivery people need to be in a good area to work... A week delivery from Ft Lauderdale will not fly in a skipper from Pago Pago.
It takes years to get the reputation and what do you ,do with your boat when away? Marinas can be expensive so you are on half dollars!
Many have to crew for a long time for free to get the reputation.
Sowing, covers, sail rite machines.... God there are so many older ladies trying to offer this one. But once cruising the need for winch covers just doesn't exist! (Btw if looking for someone to do some work, just stop past any boat with winch covers! They do it!!)
Hull cleaning. Locals come cheaper than you. Venuzalea was $10 per DAY for labour so how much can you charge for 1 hour?
Hair cutting not many do this one. But you only get $10 per cut. Many have very long hair cruising (males mid life crisis means they grow a pony tail! Women how can you bare it? I'm single. give him the heave Ho and come live with a shaved short haired non smelly man)
Consultancy work from old profession. There are few that can hide away even just giving advice. Lawyers, but is all their info now on the web or do they still need a law library?
Doing jobs for cruisers... Other cruisers seem pretty independent and don't need paid help. Making this more difficult is that most cruisers will volunteer to help someone's problem for no pay to get Karma Points.
Marine mechanic, electronics, etc. need to be in one place for a long time. Local laws etc. other cruisers won't pay. Cruiser mechanics charge too much... Generally $30 to $50 per hour when the Yanmar guy charges $50 with parts, warranty, specialist knowledge. I prefer to use the Yanmar guy at the higher rate unless I absolutely know the cheaper person.
Lots of bum alcoholics are cruising the world looking for any dollar and if you say can you do x they say yes and stuff it up. It means few will use another cruiser unless they have a great reputation.
So how would I earn money?
I think I would do the 6 months at home, 6 months cruising. No matter how poor you think your economy, it's vastly better than some island in the middle of nowhere, and in your country the dollars are real and substantial....
It's difficult... And a question asked so often... But in my four years afloat I have met NO ONE making a dollar more than just small pin money. Certainly none who are making good money.
I like this as it is most grounded in reality. However, there are ways to make money without white collar work or long-term sessilization (just made that up).
Biggest factor is going to be where you are cruising.
For me, right now, my cruising is focused in the Bahamas. A few hours a day diving with a spear gun at some good reefs will net you enough fish to sell at the local docks toward late afternoon. Right now its crawfish season (spiny lobster). Guys go out and spear 50 or 100 per day (much more using traps) and sell them for 7$ per lb.
That same lobster tail at 8 OZ goes for 28.99$ at Red Lobster right now.
So I would say small scale fishing. However, you will have to be wary about the other local fisherman. I would think to avoid confrontation you would need to either work with or for them, or limit your stays in any one place to three or four days before moving on to the next locale.