The unexpected happens sometimes during a cruise. The sailor is far from shore and his sailboat begins to take on water. In most cases, it is not because of a catastrophic incident, such as, collision with a hard object. The odds are that the water ingress is due to a split hose, a broken thru-hull fitting, or a leaking shaft log. Immediate action is necessary to locate the source of water and to stop the ingress.

Any water coming into the vessel needs immediate attention. Just a 2-inch hole below the water line allows 79 gallons of water inflow per minute. In a typical 30-foot sailboat, the hull fill up with 2,000 gallons of water in about 30 minutes.

  
This pictorial shows how the components of the rescue system interact with each other.

COSPAS: Cosmicheskaya Systyema Polska Aariynyich Sudov (Russian)
SARSAT: Search and Rescue Satellite Aided Tracking

Founded in 1982 by USA, Canada, Russia, and France.  Currently 38 nations are participating. The system only receives 406 MHz signals.