On September 11, 1999, about 1145 Alaska daylight time, a float equipped homebuilt/experimental William Diehl, Interstate S-4 airplane, N4BZ, sustained substantial damage while taking off from a private lake, at Anchorage, Alaska. The airplane was being operated as a visual flight rules (VFR) cross-country personal flight when the accident occurred. The airplane was operated by the pilot. The private certificated pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on September 13, 1999, the pilot reported he was departing from Sand Lake toward the east. While waiting for a departure clearance, he was taxiing in a tight left turn in a cove located at the west end of the lake. The water rudders were extended and displaced to the left. The pilot said the water rudders are stiff when they are deployed. After receiving his clearance, he began his departure from the cove. During the takeoff run, he left the water rudders extended. When the airplane became airborne, he said the airplane continued to turn left. He was unable to prevent the airplane from colliding with a small boat dock, and the top of a small boat. The airplane then collided with trees along the edge of the lake. In the Pilot/Operator report (NTSB form 6120.1/2) submitted by the pilot, he stated, in part: "...At rotation, could not control P-Factor of engine with max right rudder." The pilot also indicated there was no mechanical malfunction/failure. A Federal Aviation Administration (FAA) airworthiness inspector, Anchorage Flight Standards District Office (FSDO), reported that he inspected the airplane at the accident scene. The airplane received damage to the left wing, the left wing lift strut, and the left float. The inspector said the distance from the cove used for departure to the dock was about 500 feet. The distance from the dock to the trees was about 100 feet.