Our sense is that health insurance is a necessity for foreigners in the US and an option elsewhere, although as was mentioned occasionally (for us rarely) we were asked about health insurance when we entered a country. I have out-of-country coverage as part of my
retirement package that also covers things like drugs and dental when we are in
Canada. The out-of-country coverage is good for 150 days and it is may cheaper to fly back to
Canada to reset the clock on this one than to buy 'snowbird insurance' or the like. Once beyond the US, healthcare is remarkably
cheap or even free. I had a very persistent staph infection when we were in the Pacific. I went to a
government clinic in Mangareva, FP every two or three days for a month to get boils treated and dressed and they did not charge. Went to the new fancy hospital in Papeete and was in the
emergency treatment room for an hour and a half with a doctor or nurse there the whole time and it was $120. Finally went to the private hospital in
Fiji (the infection was a pain in more than one way). The doctor visit was $12 and the different antibiotics suggested (which worked!) were $6. Had a very serious hand injury in
South Africa and ended up in a private hospital. Five days in
bed, plus surgery and daily therapist treatment was $5000. If we had stayed in the
government hospital which did not have as wide a range of specialists it would have been free - even for a foreigner. Even including the hand injury we were much better off self-insuring, but we did have the 150 day coverage if we needed it.
It is not that a clear situation but most long-distance cruisers do not have health insurance. In general it is a very safe lifestyle.