(CNN) -- A U.S. Navy warship and helicopters are trailing a boat believed to be the one that was hijacked by Somali pirates over the weekend, a senior military source with knowledge of the operation told CNN. Four Americans were manning the boat.
Pirates boarded the American yacht off the coast of Oman last Friday, three days after the boat's owners split off from the relative safety of a sailing group traversing a dangerous section of the Indian Ocean, according to the group, the Blue Water Rally.
Owners Jean and Scott Adam and two others, Phyllis Macay and Bob Riggle, were aboard the yacht, the S/V Quest.
U.S. officials have made no further comment on the situation since Rear Adm. Charles Gaouette, deputy commander of the U.S. Navy's Fifth Fleet, said Saturday that the government is evaluating its options.
The Adams are experienced boaters, having started a world tour in 2004, and were very much conscious of the threat from pirates, said a friend of the Adams, fellow boater Scott Stolnitz.
Scott Adam said several weeks ago that he was concerned about pirate activity in the area, which he had never visited before, Stolnitz said. But he said Adam was determined to traverse the world himself as opposed to shipping the boat -- as some other yacht owners have done.