The two pilots, who were both qualified to fly the experimental light sport airplane, were conducting a local flight with two other similar airplanes from the same flight club. After takeoff, the three airplanes proceeded to the ocean shoreline and then flew slightly offshore along the coast. The flight was conducted at a low altitude, which, once over the ocean, was about 300 ft. Soon after reaching the ocean, both pilots noted a "skip" in the engine. They decided to climb for safety and turn around to return to their departure airport. Despite moving their respective throttles to the full throttle position, neither pilot was able to obtain full power from the engine to effect a climb, and the engine rpm began slowly decreasing. Because the airplane was no longer able to maintain altitude, control of the airplane was transferred to the pilot who held a flight instructor certificate. Due to the rocky coastline and traffic on the road along that coastline, the pilots determined that they would have to ditch in the ocean. After the ditching, both pilots escaped from the airplane, and, when the airplane began to sink, they began to swim to shore, which was about 200 ft away. Neither pilot appeared injured. No personal flotation devices were aboard the airplane or worn by the pilots. One pilot successfully swam to shore, but the other pilot drowned.The airplane washed ashore the following morning and was heavily damaged by wave action, contact with rocks, and the salt water immersion. Postaccident examination did not reveal evidence of any preaccident mechanical failures but obscuration or destruction of such evidence due to the ditching and subsequent environmental damage could not be ruled out.The examination revealed several maintenance-related discrepancies. The type of fuel line clamps used and the installation of the fuel pumps were not in accordance with the engine manufacturer's specifications, and this could have affected fuel delivery to the carburetors. After the accident, the throttle cable was found disconnected from the cockpit control, and it could not be determined whether that was a result of a partial slippage during flight, which would have limited or eliminated pilot control of the engine rpm and power.Page 2 of 15 WPR17FA146Although a similar airplane in the flight did not report any carburetor icing, the symptoms described by the surviving pilot were consistent with carburetor icing, and the ambient temperature and dew point values allowed for the possibility of carburetor icing. Despite such equipment being recommended by the engine manufacturer, the lack of carburetor heat provisions on the accident airplane prevented the pilots from being able to prevent carburetor icing, or counter carburetor icing if it did occur.Finally, although the engine manufacturer specified an overhaul interval of 300 hours, the flight club elected to adhere to a 450-hour overhaul interval advocated by a repair facility that was not approved by the engine manufacturer. At the time of the accident, the engine was about 127 hours beyond the manufacturer-recommended 300-hour overhaul interval. Although none of these discrepancies discovered during the investigation was able to be definitively linked to the accident, all were potential factors, and all were maintenance-related.The low glide ratio of the airplane (about 5:1) limited its range in the event of a loss of engine power, reducing the forced landing site options available to the pilots. The forced landing site options were further reduced by the pilots' decision to operate at 300 ft, a very low altitude. The pilots' over-water route and low cruise altitude were reported to be common for pilots in the flight club. Even though the altitude and route combination increased the likelihood of an ocean ditching in the event of a loss of engine power, neither the pilots nor the airplane were equipped for an ocean ditching. Precautions such as higher over-water cruise altitudes and water-ditching equipment, such as personal flotation devices, may have prevented this event from becoming a fatal accident.