The pilot was conducting his first flight in the two-seat experimental amateur-built airplane, with the non-certificated pilot/owner seated in the right seat. The pilot reported that the airplane accelerated and departed from the turf runway without incident; however, as it climbed to an altitude about 300 feet above the ground, he entered a left 180-degree turn. During the turn, the airplane inadvertently stalled, and descended into a pond, which resulted in substantial damage to the airframe. Both occupants were able to exit the airplane and stated that they did not experience any mechanical malfunctions or failures that would have precluded normal operation. The pilot reported about 1,600 hours of total flight experience with no previous flight hours in make and model. In addition, he had not flown at all during the previous 7 months. The owner had accumulated about 30 hours in the accident airplane. He stated that he had seen the pilot flying other airplanes in the past and assumed he was capable of the flying the accident airplane.