Robert Stephens and Paul Waring, of Stephens Waring Design in Belfast, Maine, do much more than design beautiful, fast and innovative boats. Now they’ve done a comparison of real estate and boat prices in Portland, Maine, to see if it costs more to live near the water or on the water. Their answer: In a side-by-side comparison of actual living space, floating residences (including houseboats, floating homes and live-aboard boats) come out ahead; it’s considerably cheaper to live on a boat. And they have maps and charts to prove their point. Stephens and Waring looked at upscale neighborhoods near the…