I would agree with Grahame's excellent points with two exceptions--one is the necessity of thrusters with a single diesel. (If I interupt his response correctly). The other would be a single steering and control center. I have had several experiences where one steering pump went out, and the other was still usable--same with controls. Push/pull cables are quite reliable and relitatively free of maintance, the added convience and safety of a pilothouse plus flying bridge controlls over come the maintance of dual controls in my experience. I don't buy that 10% is a given number: There are too many variables, such as slip rent which may range from almost free (a mooring, at anchor, or owning waterfront home with a slip--the appreciation more than "pays for the taxes and interest".), to over $30 a foot a month, insurance depends on the area and other factors, taxes can also vary. Bob Austin