Prior to the glider tow flight, the pilot estimated that he had about 45 minutes of fuel on board; he also estimated that the flight would take about 12 minutes. The pilot reported that he did not visually check the fuel level prior to departing, but relied on the sight gauge. After releasing the glider and while in the descent, the engine lost power. Judging that he could not make the airport, the pilot landed just off shore in the ocean surf. A postaccident examination of the engine and propeller revealed no apparent damage to the propeller, and that when rotated there were no abnormal sounds detected from the engine. An examination of the airframe revealed that both ailerons were damaged, the fuselage was deformed, and the rudder was damaged. Additionally, when the fuel tank was inspected, which had not been breached, it was observed to be empty. The pilot reported no preimpact mechanical malfunction or failure that would have precluded normal operation.