If you live anywhere near water or watch old Miami Vice reruns, you've seen go-fasts--those garish, arrogant, pencil-hulled runabouts, with their big V8s bellowing through open pipes. What you probably haven't seen, and wouldn't believe if it did blast past your porthole, is the 118 WallyPower. You haven't seen it because there's only one, and it's in the Mediterranean. You wouldn't believe it because this narrow, angular, black-glass-housed superluxury go-fast is 118 feet long, looks like a stealth fighter that missed the runway, and is squirted to a top speed of nearly 70 mph by a total of 16,800 gas-turbine horsepower. Price? $24 million.