By now, the double takes are routine. Drivers and pedestrians pass the warehouse, then creep back and squint to confirm what they think they have seen: a 47-foot aluminum boat freckled with rivets, crowned with a lime green cockpit and tattooed with a stylish American flag.

The Euclid Avenue industrial corridor in Manassas is an unlikely home for a mutant 12,000-pound vessel that has 10 times the horsepower of a car and can slice waves at 150 mph. Yet driver James Sejd and throttleman Ken Silverman guided the craft to the top of the Super Boat International national points standings last year in the Limited class.

"It's hard to believe we have a nationally known championship offshore racing team centered in Manassas and that we have everything we need right here," Silverman, 49, said of the team's easy access to skilled labor, parts and supplies -- some available within walking distance of the warehouse.

Manassas resident Sejd (pronounced SHADE) and Great Falls sidekick Silverman, teammates for the past five years, might be champion powerboat racers, but they never will win any awards for inconspicuousness. When hauling the $750,000 craft, dubbed "Riveted" because of its Italian handcrafted aluminum design, the truck and boat combine to hog 84 feet of interstate. The team needs a forklift to squeeze the craft out of the garage and a crane to deposit it into the water.

"When we're on our way to Florida or New York or wherever, this is a big deal when you pull up in front of a hotel," Sejd, 39, said with a chuckle. "It's big, and it's expensive to work on, but as soon as you put it in the ocean it's just a little speck. Even the smoothest days out there you wish you had something bigger."

Those smooth days can be rare, so the boat is equipped with ship-to-shore radio, fire suppression systems, flotation bags and emergency air, all among items on an exhaustive 10-page checklist the team repeatedly reviews in the days before a race. Medical support in helicopters, including jump divers, shadow their every move.

A similarly sized boat once landed on deck at 100 mph, the typical race speed, and a smaller boat once broadsided Riveted. The team has weathered 12-foot waves and 40 mph winds in South America.

"A surfer stays out all day waiting for those big waves," Sejd said. "Those big waves are out there, and you never know when they're going to be there. . . . The road surface never changes in car racing. Our road changes every 10 feet."

"Everybody says owning a boat is like standing in the shower and ripping up $20 bills," Silverman said. "Well, race boating is like ripping up $100 bills while hitting yourself with a hammer. A good word for it is violent. At those speeds, the surface of the water is like concrete."

An Elite Class

Sejd, owner of American Stripping Company in Manassas, and Silverman, who works for an automobile dealer management company, have graduated this year to the highest class of offshore racing: Superboat. The team is in second place in the point standings headed into the next event, in Deerfield Beach, Fla., on July 18.

There are only about a dozen boats worldwide that compete in the Superboat class. There are fewer restrictions than in the other classes, which gives the Riveted team and eight-member crew greater flexibility with their two 1,350-horsepower engines (price tag: $65,000 apiece).

The endeavor is too expensive to be called a hobby. Sejd said his annual operating budget is just under $1 million, defrayed by sponsorships, appearances and purses that range from $10,000 to $25,000. The Riveted team maintains a rotation of six engines because after every two races the two in the boat must be rebuilt. The boat burns 230 gallons of fuel an hour at $5 a gallon.

"Everybody works 12-hour days and comes over here and works at night or on the weekends, and the grass doesn't get mowed at home," said Sejd, whose garages -- one here and one in Miami -- bustle with activity in the weeks leading up to the 10 or so races a year.

Most of the boats Riveted competes against are made of fiberglass, favored for its light weight, sturdiness and standardized construction. But Sejd prefers aluminum because it is more predictable for strength and safety.

"Fiberglass is a great material," Sejd said, "but they don't build jetliners out of it. They do build 747s out of aluminum."

Getting to the Top

Sejd was still in his teens when he started modifying the engine in the pleasure boat he would take out on the Potomac River. That led to even mightier engines and, eventually, to the purchase of a larger boat. That, as a result, yielded even further engine experimentation.

"I thought I was the fastest guy in the world," Sejd said. "I took it out to race professionally, and it turns out I'm the slowest guy out there, and everything I thought I was doing right was wrong."

The typical race, 120 miles on a seven-mile oval course, takes about 90 minutes. Though powerboating attracts tens of thousands of spectators in Argentina, Sejd considers it more of a TV sport. ESPN2 shows delayed telecasts of many races.

As the driver, Sejd's job is to peer a mile or so ahead to keep track of other boats and watch for changing water conditions. There could be a thunderstorm on one end of the course and lapping waves on the other. He sits and steers from the right-hand side of the canopy, similar to a cockpit.

As the throttleman, Silverman, a former Old Dominion Speedway stock car racer, must maintain tunnel vision. He monitors the gauges and instruments and controls the speed.

As intricately as the vessel and engine are designed, and as innovative and perceptive as the crews are, not every Riveted feature is highly sophisticated: There are numbers duct-taped to the right of the driver.

"That's the high-tech way we keep track of laps," said Sejd, who already has the numbers in place for the next race. "Every time we go around, it's my job to pull the tape off."

Riveted's signature number is the "74" painted on its side, though by finishing first in its class in the country last year, the boat is authorized to flaunt "U.S. No. 1."

The crew will leave the boat alone. When the team sported No. 1 in 1997, the boat was not nearly as successful. So the Riveted crew is sticking with 74, the number Silverman wore as a University of Virginia lacrosse player and the number that served him well when he raced stock cars.

Besides, the boat is usually squirreled away in a warehouse, and to nonracers who ogle the craft, the No. 1 would mean nothing.

"It's kind of bragging rights," Sejd said. "But those people we have to impress already know."

CAPTION: James Sejd, 39, is driver of Riveted, a 47-foot, 12,000-pound aluminum power boat with 10 times the horsepower of an automobile. Along with throttleman Ken Silverman, Sejd guided boat to first last year in Limited Class of Super Boat International national points standings.

CAPTION: Equipped with ship-to-shore radio, fire suppression systems, flotation bags and emergency air, Riveted costs $750,000 and cuts waves at 150 mph.