On September 3, 2017, about 0920 eastern daylight time, a Piper PA-32R-300, N544DG, was substantially damaged when it collided with water during takeoff at Merritt Island Airport (KCOF), Merritt Island, Florida. The private pilot and three passengers were not injured. The personal flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and a visual flight rules flight plan was filed for the planned flight to Marsh Harbour International Airport (MYAM), Marsh Harbour, Bahamas.The pilot reported that prior to the flight, he fueled the airplane to a total of 80 gallons of 100-low-lead aviation gasoline. He then completed a preflight inspection of the airplane and subsequent engine run-up prior to takeoff, with no anomalies noted. The pilot added that although the automated surface observation system reported the wind from 350° at 5 knots, the wind was light and variable at the time of the accident. Additionally, an airplane was in the airport traffic pattern and using runway 11, so the pilot elected to depart in that direction. The pilot initially stated that he extended the flaps "two notches" and rotated the airplane at 80 knots, about two-thirds down the 3,601-foot asphalt runway. He later stated that the flaps were retracted during the takeoff attempt. A witness, who was a flight instructor at a fixed-based-operator, was standing near a hangar and observed the accident takeoff. The witness stated that his attention was drawn to the accident airplane as it used more of a ground roll during the takeoff attempt than what he was accustomed to seeing. Specifically, the airplane did not rotate until about 2,300 feet down the runway. The nose initially pitched up about 5° and the airplane climbed about 20 to 30 feet above ground level. Then, as the airplane approached trees, the nose pitched up about 15° and the left wing dropped, consistent with a stall. The witness added that the pilot initially reported the engine "quit," but the witness heard engine noise throughout the takeoff, until the airplane impacted the water. Review of airport surveillance video revealed that the airplane had not lifted off as it traveled off the right side of camera view, about 600 feet prior to the departure end of the runway. Examination of the wreckage by a Federal Aviation Administration inspector did not reveal any preimpact mechanical malfunctions. The inspector rotated the propeller and confirmed crankshaft, camshaft, and valve train continuity to the rear accessory section of the engine. During rotation, the inspector noted saltwater emitting from the exhaust. The inspector did not attempt a test-run of the engine as saltwater remained in the engine and had corroded one of the magnetos. The pilot provided weights of the occupants and baggage, and estimated 75 gallons of fuel onboard at takeoff. Based on information provided by the pilot, the airplane was about 117 lbs. below its maximum takeoff weight of 3,600 lbs. The witness estimated 12 bags on board and their combined weight more than double the 100 lbs. that the pilot reported; however, the bags were wet after the accident and could not be accurately weighed. Additionally, the airplane held a total of 94 gallons of useable fuel and the exact fuel load during the takeoff attempt could not be determined. The recorded weather at an airport located about 8 miles southeast of the accident site, at 0853, was: wind from 330° at 6 knots; visibility 10 miles; few clouds at 6,500 ft; temperature 26° C; dew point 24° C; altimeter 30.09 inches of mercury. Review of a pilot's operating handbook for the make and model airplane revealed that at 80° F, with flaps retracted, at 3,600 lbs., with a 3-knot tailwind, at sea level, the airplane required about 2,900 feet to clear a 50-foot barrier. The data assumed a liftoff speed of 64 knots and a barrier speed of 69 knots.