The captain and a crew member of a tugboat died of exposure today while another crewman escaped serious injury today after their craft sank in the Chesapeake Bay south of the Maryland capital, according to the Coast Guard.

Capt. James Reese and crewman Bruce Volpe died at Patuxent Naval Hospital. A third crew member, Paul Harpold, was treated at the same facility and released. The Coast Guard rescued all three after their 40-foot tug, the Blair, sank off Thomas Point about 10 miles south of Annapolis harbor.

The Coast Guard said the cause of the sinking is under investigation.

The tug was owned by Baltimore Launch Services, Inc., according to Stokes Lott, the firm's general manager and chief operations officer. He refused to comment on the accident.

Authorities said the tug, which was towing a barge, issued a Mayday -- or vessel in distress -- call at 6:45 a.m.

But the Coast Guard said efforts to reach the vessel by radio failed and that a Coast Guard boat and another tug were sent to aid the tug, which had sunk.

Two of the crewmen were pulled from the water, and a third crewman was rescued from the barge, according to Lt. Scott Newsham. The crewmen were taken by Navy helicopter to Patuxent.

The Coast Guard said two of the men had been in the water about 50 minutes when they were rescued about 8 a.m. Authorities were not able to say who was in the water and who was on the barge.

"Apparently all three men abandoned ship, one was able to get on to the barge they were towing. The other two were picked up out of the water," Newsham said.