I take it that when you say BOAT you mean a real boat, one that can be cruised, perhaps even to places like the Bahamas, not a dinky trailer boat that does not live on the water & is not for cruising.
Boats are waay more expensive to buy & operate than any RV. $200,000 really does not buy much of a boat, even a used 38-40' trawler. Most boats big enough to live on measure fuel in how many gallons are burned per mile rather than miles per gallon.
Maintenance is much higher than any RV class. Marina fees are charged on the per foot basis. You had better be pretty handy at fixing things yourself when out on a boat. There is no roadside assistance & the consequences of a breakdown can be catastrophic not simply inconvenient as it is with a RV.
Yes, I do own a boat. Only a 32'er, single diesel powered, but it has all the systems of a RV & more to take care of.
My view is, if you get somewhere where there is water & you get the boating itch, rent one. Much cheaper.