In my case, I just keep working. Social Security income isn't much, and retirement, according to my wife, ain't gonna' happen until three days after I'm dead and buried. Fortunately, as a freelance writer/photographer, and a musician/entertainer, I can usually find work in every port, and sometimes while at sea.
Next fall will be the real challenge. I'll be heading south down the ICW in early October, making lots of stops along the way, and with luck selling lots of stories to magazines and possibly a hometown newspaper. That should pay all of the sailing expenses including food, dockage and beverages. With any kind of luck, I'll end up somewhere in the lower Florida Keys, playing music in Tiki Bars at marinas and other locations. That money will be sent back home to pay the extortion fees such as real-estate taxes, etc...
While I'm confident there are places where you could invest your money and get a decent return, I'm just not smart enough to do that. Warren Buffet knows stuff like this, but I've never been good at looking into the future of a company and having the wherewithal to make those kind of investments.
I guess some of this may have to do with the age of the person that hopes to make the voyage. If you're an old codger like myself, your spending habits tend to decrease with age. This is probably because there's not a lot of material things older sailors really need. I'm happy as a clam when anchored up in a quiet cove, cooking some real, Polish kielbasa on the grill and sipping an ice-cold Margaretta. Someone half my age might be heading for a high-priced restaurant, sipping overpriced booze and hoping to hook up with an attractive member of the opposite sex. Now that could be an expensive evening.
Now, if you happen to discover that high-dollar-return investment site you're looking for, don't be bashful about sharing the information with the rest of us. Who knows, maybe I could retire before I'm dead--NAH!