It's an old joke -- a boat is a hole in the water you pour money into. It's also true. Some 95 percent of owners have boats 26 feet or less at an average cost of 18 grand, according to Ellen Hopkins at the National Marine Manufacturers Association, and more than 80 percent of those buyers shelled out for pre-owned boats. The actual boat purchase is just a start, however. Bentley Collins of Sabre Yachts says to budget 10 percent of the boat's value annually to cover additional expenses. And then there are the extras.