Powerboat Cruising info needed
My wife and I have a 32'' sailboat in the Chesapeake Bay and we do far more powering than sailing because of light winds. Our cruising speed under motor is about 6 knots.
Maybe you should consider buying a sailboat and motor it wherever you go. No law says you have to hoist the sails. A 38'' sailboat should motor at the 8 knots you desire, can be purchased for less than the chugger (if you are patient in looking for one) and will stand up to high seas if you get surprised off the coast in a blow.
You could add to the fuel capacity to increase your range. The engine will likely have far fewer hours on it than a similar sized powercraft and be smaller and simpler to work on (mine is a three cylinder Volvo). It might, also, provide better fuel economy. We burn about 8 mpg.