On May 19, 1993, at 1407 Alaska daylight time, a float equipped Cessna 180H, N8237V, registered to and operated by the pilot in command, crashed into Ketchikan Harbor during initial climbout from the seaplane harbor in Ketchikan. The commercial pilot and the one passenger were not injured and the airplane was destroyed. The intended destination of the 14 CFR Part 91 flight was Lake McDonald. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed. On the morning of May 20, 1993, the pilot and passenger were interviewed separately by telephone by the NTSB investigator in charge. The pilot said that as part of his pre departure preparation, he drained the wing tanks and engine fuel sumps, conducted an engine runup and performed a flight control continuity check. Confirming that the plane was airworthy, he commenced a takeoff from the sea plane harbor on an eastbound heading. He climbed straight out at an indicated airspeed (IAS) of 80 to 85 miles per hour which provided a relative flat attitude and rate of climb of 100 to 200 feet per minute. Up to this point in the flight, the air was smooth and stable. At approximately 400 feet above the water, he initiated a 15 to 20 degree right banking turn toward Gravina Island. The pilot said that as he was in the process of rolling out of the turn the flight encountered without any prewarning a severe downdraft which he likened to the sensation of descending in an elevator. He applied full engine power, pointed the plane's nose earthward, and initiated a "hard right banking turn of 45 to 50 degrees" to parallel the islands shoreline. He glanced at the airspeed indicator and observed an IAS of 70 mph. The stall warning horn did not go off and there was no buffet indication of a stall. Just prior to contacting the water, he brought the plane's nose up to the horizon. The airplane contacted the water in a relatively flat attitude. The passengers comments essentially paralleled those of the pilot. Both the pilot and the passenger reported that there were no problems with the engine. A commercial pilot who departed along the same route as the accident flight approximately 15 minutes after the accident reported that the air was stable and that no down drafts were encountered. On the day of the accident the Flight Service Station (FSS) in Ketchikan did not receive any pilot reports of severe downdrafts in the Ketchikan Harbor area.