Somali pirates say a hijacked yacht carrying four Americans is expected to reach land in Somalia on Sunday.

U.S. officials have been weighing possible responses to Friday's hijacking of the SV Quest  off the Somali coast.

The ship is the home of Scott and Jean Adam, who have sailed the world for several years distributing Bibles in a variety of countries.

Organizers of an international yacht race identify the two other Americans on board as Phyllis Mackay and Bob Riggle. The organizers of the Blue Water Rally say the four sailed the race for several weeks but went off in a different direction February 15.

Somali pirates usually attack commercial ships instead of yachts.  However, pirates held a British couple, Paul and Rachel Chandler, for more than a year after seizing their yacht in October 2009.

The pirates have made hundreds of millions of dollars seizing merchant ships for ransom in recent years.

A number of pirates have been caught and prosecuted. On Wednesday, a New York judge sentenced a Somali pirate to 33 years in prison for his role in the 2009 hijacking of the U.S.-flagged Maersk Alabama.  

But for the most part, international naval patrols off Somalia's coast have had little success in stopping pirates from attacking ships in the Gulf of Aden and Indian Ocean.

Estimates vary, but the pirates are believed to currently hold at least 31 vessels and about 700 hostages.