The two occupants of an offshore powerboat participating in a race Sunday off Patchogue were killed by the pressure of water forced into the hull after it flipped on its side, a preliminary investigation has found.

That is the initial assessment of Ed Smith, president of the Offshore Performance Association, which organized the race.

Phil DeJana of Bayville, and Kevin Graff of Port Washington, were killed when their 37-foot Marine Technology Inc. twin-engine catamaran flipped at between 90 and 100 mph during the Battle on the Bay powerboat race in Great South Bay.

Like an Indy 500 or other professional race car, the current generation of offshore racing powerboats is designed with an array of safety features to allow the occupants to survive a crash. So industry officials are stunned that the accident killed both members of the crew.

The helmsman and throttle man are protected by six-point racing harnesses, bulletproof canopies and a protective impact-absorbing capsule, and there are scuba tanks so they can breathe if submerged while awaiting rescue.

Offshore races have been held on and off around New York and Long Island since the 1960s and the safety record has improved with the technology since millions of dollars in research was done after a 1986 fatal accident.

DeJana, 62, was vice president and a principal in DeJana Industries Inc., a Port Washington road maintenance company that employs 130 people in several states, but friends described him as just one of the guys. He had been racing powerboats since at least the 1980s and had moved up to bigger and more powerful boats.

A mechanic for his company, George Idze, 35, said "although he was on the top of the company, he always was part of a team with us."

Graff, 48, was an electrician who loved racing speedboats and he had been at it at least 10 years. Jerry May, a friend, said "he went doing what he loved to do in a blaze of glory. He loved living on the edge."

Billy Frenz, executive director of the Connecticut-based National Powerboat Association, which sponsors offshore powerboat races on the Hudson River and other venues, said he knew the two racers from the 1980s when they were racing a smaller catamaran.

"This is their second year with that boat," said Frenz, who was at the race. "Last year he had smaller power," twin 525-horsepower engines.

"This year he moved up to twin 750s and moved up a class" from Cat Light for light catamaran to Extreme. "He could run 150 miles an hour now."

Frenz said the larger boat included a closed capsule around the crew to protect them and a scuba tank for each person "so they should be able to breathe a minimum of eight minutes" while awaiting rescue.

"It's hard to understand why this happened because with today's safety standards it really shouldn't have happened," he said.

He said the safety equipment is inspected before racing by the sanctioning organization.

The boats are made of Fiberglas or polyester resins to resist damage, Frenz said. "I don't understand why it has an eight-foot gash on the starboard gunwale unless it violently hooked because Great South Bay is calm," he said. "These boats are made to run in the ocean. So this thing should not open up or crack in Great South Bay. It's considered a pond" by ocean racers.

He said the bay is also not known for having floating debris like the Hudson River where he organizes races.

"Years ago we were losing people left and right," Frenz said. "With this new generation of boats, this shouldn't happen."

The Coast Guard said it does not have data on powerboat race accidents because they are generally investigated by the states. The agency issues permits for the race and handles security to protect observers but leaves the other safety issues up to the sanctioning organization.

The incident occurred at about 4:30 p.m. south of Shorefront Park, which served as race headquarters and where spectators gathered to watch the event.

The race came to an abrupt end as the injured racers were removed by a diver and a Suffolk County police boat pulled the damaged vessel to the dock. An eight-foot gash was visible on the right rear side. Flags in the park were lowered to half-staff.

Coast Guard Petty Officer 1st Class Jeremy Clouse, coxswain of a 25-foot response boat on scene, said, "We were enforcing the security zone around the race and I noticed the water going everywhere. The other 25-foot boat crew was already at the wreck, with two Coast Guardsmen in the water trying to do what they could to get the people out. One of the race helicopters dropped a diver who was able to get the emergency hatch open and pull the victims out."

The two men were transferred to a local fire response boat, which took them to emergency medical service personnel waiting onshore. Both were pronounced dead at a hospital.

Jim Poplin, the race safety director, said the Offshore Performance Association, as sanctioning body for the race, will take the boat apart and reconstruct it to determine the cause.

Between 40 and 50 craft took to the waves during the event, sponsored by Great South Bay Racing Inc., OPA Racing and the Village of Patchogue. More than 5,000 spectators watched the race from the shore and at least another 500 watched from their own boats.