Could rescuers have reached the Lady Mary sooner if her distress signal had been more detailed?

That's one of the questions federal investigators have said they want to answer after the scallop boat sank before dawn Tuesday 75 miles southeast of Cape May, killing six men.

The Lady Mary apparently was vulnerable in a way that is surprisingly common.

Unregistered EPIRBs - emergency position-indicating radio beacons - send out less information than those that are registered. The Lady Mary's was unregistered, a U.S. Coast Guard spokesman said.

That oversight can slow emergency response, according to the satellite consortium that relays distress calls, Cospas-Sarsat. But despite the government's and boating industry's reminders to register for the nationwide database, for free, plenty of EPIRB owners do not do so.

West Marine, the nation's largest boating-supply retailer, says in its 2009 catalog that 20 percent of EPIRBs it sells remain unregistered. Calls to the National Oceanic and Atmospheric Administration to learn a more exact figure were not returned Thursday.

Chris Wyler, of EPIRB manufacturer ACR Electronics, said, "We have been told that upwards of 70 percent are registered with NOAA."

According to Cospas-Sarsat, 600,000 digital EPIRBs were in use in 2007. Analog EPIRBs have since been removed from service.

The Coast Guard inspects scallop boats every year, and inspectors check EPIRB registration. Herb Hoeger, of the Coast Guard auxiliary, inspects 30 to 40 boats each year, although not the Lady Mary, he said.

Vessel owners can register online, by telephone or through the mail.

"They may have sent in for registration," Hoeger said. "Maybe it didn't go into the computer yet."

Rescuers retrieved the Lady Mary's EPIRB floating near the sink site but have not disclosed its model. Owner Royal "Fuzzy" Smith Sr. said the device was "brand new," and most new EPIRB models feature a global positioning system, which also helps expedite rescue efforts.

At 5 a.m. Tuesday, the boat sent out a distress signal, which the Coast Guard did not receive until about 7:30 a.m. Rescuers arrived an hour later and retrieved three of the seven crew members. One of the three survived. The four missing are presumed dead.

"I dont understand how this whole scenario happened," said Kirk Larson, the longtime scalloper who is mayor of Barnegat Light in Ocean County. "It's a shame. It probably never should have happened."