DOVER, Del. -- A liftboat that foundered off the Delaware coast in heavy seas, leaving one of two crewmen dead, was exempt from regulations for that type of vessel because it was being used for research purposes, Coast Guard officials said Tuesday as they began an investigation.

Bluewater Wind LLC, which is trying to win state approval to build an offshore wind farm that would supply electricity to Delmarva Power, was using the Russell W. Peterson to study migratory bird routes in the Atlantic Ocean off Rehoboth Beach.

Had the research vessel been subject to same requirements governing other liftboats, it likely would have had at least three crew members aboard, instead of only two, when it was crippled by high winds and heavy seas early Monday, 14 miles off Rehoboth Beach.

The names of the dead man and the surviving crewmember were still being withheld Tuesday.

Petty Officer Christopher McLaughlin, a spokesman for the Coast Guard in Atlantic City, N.J., said that when the captain of the vessel radioed for help, he reported that he couldn't leave the helm to check on the other crewman.

"He couldn't leave the helm because he was still trying to steer it," McLaughlin said.

Coast Guard regulations require liftboats of the Peterson's size operating in open waters to have at least three crewmembers. But in being put to use as a research vessel earlier this year, the Russell W. Peterson was no longer subject to liftboat regulations.

"They were properly manned," said Coast Guard investigator Michael Kaszuba. "If it was considered a liftboat ... it definitely needs a master and two deckhands."

Liftboats are self-propelled vessels with open decks and barge-shaped hulls that are equipped with metal legs that can be lowered to the seabed, raising the hull above the water to serve as stable work platform. They often are used to perform maintenance on oil and gas well rigs.

Before being acquired by Aqua Survey of Flemington, N.J., which brought the vessel to Delaware and rechristened it in March, the Russell Peterson was used as a liftboat servicing oil platforms in the Gulf of Mexico.

In addition to manpower requirements, liftboats are subject to certain maintenance regulations, including inspection of their legs at designated intervals. Details on any such inspections of the Russell W. Peterson were not immediately available.

"We're all just trying to deal with the loss of a colleague right now," said Aqua Survey president Ken Hayes, who refused to answer questions about the vessel's history or operations.

Kaszuba said he had not had a chance to interview the surviving crewman, but that investigators believe the vessel was elevated above the water when one its three legs, or spuds, buckled.

"We believe that the vessel was on its spuds, and that it experienced some severe weather and one of the spuds may have given way," he said, noting that the starboard leg may have buckled.

Conditions at the time included seas of 8 to 10 feet, with occasional swells of 12 to 14 feet, and winds between 30 and 40 knots.

Coast Guard officials said any weather-related restrictions on operations would be up to a vessel's owner.

According to a 2003 Coast Guard subcommittee report on liftboat operations, casualties involving elevated liftboats often are associated with "punch-through," when a single leg suddenly penetrates into the seabed faster than the crew can compensate by jacking the legs up or down, thus putting stress on the vessel structure.

Kaszuba could not immediately confirm that the legs of the Russell W. Peterson, which was built in Louisiana in 1980, had been shortened from 105 feet to 70 feet before it was brought up from the Gulf of Mexico.

"If there were any modifications, we're getting all the records that the owners have," he said.

According to Coast Guard records, the vessel was subject to two enforcement warnings in July 2007 after a non-casualty investigation in Morgan City, La. Kaszuba declined to disclose details of the warnings without a Freedom of Information Act request.

While the Peterson was no longer considered a liftboat or offshore supply vessel, officials noted that Aqua Survey also did not request that it be designated a research vessel, a category that carries its own regulatory requirements.

"The regulatory regime is a little more relaxed," explained Coast Guard Commander Kyle McAvoy.

The result was that the Peterson was declared an uninspected commercial vessel, subject to even less stringent regulations.

Aqua Survey is working with state and local agencies to salvage the vessel, which ran aground near Bethany Beach.

The salvage operation commenced at about noon Tuesday.

Coast Guard officials said there was a sheen coming from the vessel, but the impact to the environment is deemed minimal.