I spend a lot of time on the stock market.
there is nothing paying a solid 8%. DRI pays 4%, And I do hold that security.
To make 8% requires active investing, so now your budget would need internet as well. Thats ok if your cruising the US coast, not so in Tahiti.
True, "...nothing pays 8%..." if it were that easy, we'd all be sailing....
I use a combination of investments which are for specific goals.
Food, and essentials; lowest risk.
Entertainment; higher risks.
It can be done and it is "active", requiring a monthly review and constant awareness.
The Net and Markets are both Interests of mine and are included in cruising plans.
Fortunately, its easier to find free WiFI spots nowadays in Mexico and other areas than in the US. It may have something to do with not everyone having internet to every house, and a less-fierce charge-everybody-for-everything culture
You are correct (and professional) to caution the readers on returns.
A Cruising group of investments do NOT try to get rich, or even "make money" in the traditional sense; simply keep some cash flowing in and preserve Principal.
The eight works for me as a target, and usually leaves a bit left over at the end of the year.