If a man is measured by his wake, Charlie Plumly's quite a guy. Not that he is finished with this world yet. His wake was just temporary as he recently breezed down the Potomac at 32 knots, pulling half the river behind him in a mountain of displaced tidewater.

He is skipper of Conair, a jet-black, 60-foot, 47-ton Riva Black Corsair that looks like something one of Adnan Khashoggi's arms procurers might bomb around the Mediterranean in, which is exactly what it is.

Inch for inch, the Riva Black Corsair is perhaps the most expensive and purposeless yacht in the world. It single-handedly lifts the concept of conspicuous consumption, not to mention the mountain of water behind it, to new heights.

The price varies with the exchange rate for the Italian lire, but at the moment this cozy little express day-cruiser with bunk space for four goes for about $2 million, which is just the ante, thanks.

She goes nowhere without a full-time engineer to care for her twin, German-made, 1,300-horsepower MTU diesels, which gulp fuel at up to 160 gallons an hour. She carries 1,200 gallons of fuel oil and measures cruising range by the proximity of the next supertanker.

So prodigious is Conair's fuel consumption that when Plumly took her from here to Annapolis, he didn't pull up to the gas dock first -- the gas dock bloody well came to him. He called Southeast Suburban Fuel and had the fellows come down and run the hose across the water so he could take on a truckload. When he hit Annapolis five hours and 500-600 gallons later, he was hunting the Gulf sign again.

But if you have to ask the price, of course you can't afford it, so just sit back and enjoy the ride. You probably couldn't find one to buy, anyway. There are only five Riva Black Corsairs, one of which is in fact kept by a top Khashoggi associate in Monaco, Plumly said, and another by a fellow he described murkily as "a merchant from Istanbul."

What do these boats do? Well, they roar, hell-for-leather, pleasure-bound, from port to port.

"Usually," said professional skipper Alistair Simpson, who is in town seeing after former D.C. Transit magnate O. Roy Chalk's 100-foot motor sailor at Gangplank Marina, "the owner sends a boat like that ahead with his paid crew, then joins them for a day or two at a time. It's a toy."

Ah, but what a toy. Simpson, who said he briefly skippered the first Riva Black Corsair, made for a man on the Mediterranean, calls it "the Rolls Royce of fast boats."

And from the moment Plumly clicked it into gear and started burbling down Washington Ship Channel on the way to Annapolis, going as slowly as he could, which is six knots under one engine at idle, you could see how the comparison fit.

Okay, so Miami Vice boats are hot. This looks like a Miami Vice boat times three, but appearance is where the similarity ends. Miami Vice means speed. Riva means speed with comfort, and that's spelled M-O-N-E-Y.

If you've ever been on one, you know most Cigarette-style speedboats look better than they feel. They're so narrow, they wallow in a sea, so low they have few accommodations. In some, a man has to kneel just to use the head. They're so light they pound mercilessly in the mildest chop. They're noisy, overpowered and unwieldy to run -- in a word, tacky. Nouveau, if you will.

Now compare the Riva, with black Italian lacquered built-in cabinets; two full bathrooms, one with bidet; Rosenthal china and Ricci Sterling silver for formal dinner for eight; air conditioning; stereos in every cabin; leather settees; laminated birch bulkheads; three refrigerators; Oriental rugs, even a cappuccino-maker in the galley.

So meticulous is attention to detail that even wind flow over the cockpit is refined. At 32 knots, a man can sit at the teak cockpit table and nearly effortlessly read the morning newspaper.

Of course, this attention is bestowed principally on the owner. "You might have noticed," said Plumly, a distributor for Riva in Stamford, Conn., "that in all that beautiful cabin area below there's not a single handhold. When I took my wife out one day and the weather came up, we found out the only way to move around down there in bad conditions is on your hands and knees.

"Naturally," he added merrily, "the owner wouldn't worry about it. He'd have the crew take care of a passage like that."

Now about that wake. Plumly, a retired Navy captain, is a wonderful skipper but he has the powerboater's disease, a childlike glee at leaving chaos behind him.

The Riva Black Corsair numbs the senses. You're schussing along at 30-plus knots with enough power to pull 100 waterskiers, the engines muted to a mild and satisfying roar over which normal conversation is possible. So who is thinking about the raging crests that roll away from the transom?

Plumly is.

"Did he spill his coffee?" he howled as a cabin cruiser went lurching over Conair's tsunamis near Mount Vernon.

"Has that guy stopped shaking his fist yet?" he wondered mirthfully after rolling a sailboat's gunwales under water off Thomas Point.

This is a wake you have to experience to believe. Plumly got the chance off Patuxent Naval Air Station when he passed a destroyer, the Spruance, and circled it for a look.

Ka-Bam! Bam! Bam! Conair rocked in mid-circle.

"Wow! That was our own wake," laughed the engineer, Bill Nagle, "and there's the rest of it." He pointed across the water to towering whitecaps rolling away toward shore on the otherwise dish-calm Chesapeake.

This wake ought to be registered as a deadly weapon.

Truth is, practically everything about Conair is already registered with the authorities somewhere, so often has it caught the attention of law enforcers. Plumly said on the way up from Florida he was stopped every day by either local lawmen, Drug Enforcement Agency officers or the Coast Guard.

Looking for contraband, of course.

This boat just has that look.