On September 4, 2004, approximately 1920 Pacific daylight time, a float-equipped Piper PA-18, N2415P, impacted the waters of Drayton Harbor, Blaine, Washington, while on final approach for a simulated engine-out landing. The flight instructor and his private pilot-rated dual-student both received minor injuries, and the aircraft, which is co-owned by the flight instructor, sustained substantial damage. This segment of the 14 CFR Part 91 instructional flight, which was initiated about five minutes prior to the accident, was being operated in visual meteorological conditions. No flight plan had been filed. There was no report of an ELT activation. According to both the dual student and the flight instructor, the purpose of the flight was to continue the student's training process toward his upcoming single-engine seaplane practical flight test. On the day of the accident, the student had completed four takeoffs and landings to a full stop, and then after landing to refuel the aircraft, the instructor told his student that they were going to practice crosswind landings. As the student was climbing through 400 feet above the water, the instructor pulled the power to idle and instructed the student to execute a simulated engine-out landing. The student then established the aircraft in a controlled slip in order to descend to the point at which he wanted to touch down. When the aircraft was about 50 feet above the water, still in a slip, the instructor, who had just warned the student to watch the airspeed, sensed that the aircraft was about to enter a stall. The instructor therefore pushed the throttle full forward and pushed forward on the control stick. Within two to three seconds after the instructor made these inputs, the aircraft impacted the surface of the water in a 30 to 40 degree nose-down attitude. According to the student, he had been repeatedly checking to make sure the airspeed was at 60 mph during the approach, and when the instructor told him to check the airspeed, it was still at 60 mph. It was the opinion of the student that the aircraft was not about to enter a stall, but that the instructor misinterpreted some light turbulence and the wing-low attitude created by the slip as the beginning of a stall. According to the student, he looked at the airspeed just as the instructor took control of the aircraft, and it was indicating 60 mph. After the accident, the co-owner of the aircraft, who is an airline transport pilot and the father of the instructor, made arrangements with a local commercial operator to remove the aircraft from the waters of the bay. The aircraft was then removed from the bay and taken to a location near the home of the co-owners. Neither owner/pilot notified the NTSB that the accident had taken place, nor sought permission from the NTSB to move the wreckage. The NTSB became aware of the accident when a witness reported the occurrence to the FAA, and the FAA passed the information on to the NTSB. According to an FAA Airworthiness Inspector who inspected the aircraft after the accident, there was no indication that there had been any anomaly in the flight control system, nor any indication that there had been a problem with the engine. It was the opinion of both pilots that there had not been any malfunction of the airframe or the engine.