On June 16, 2013, about 1620 Hawaiian standard time, a Piper PA-28-181, N9160Q, was substantially damaged during an off-airport landing following a reported loss of engine power near Waihee-Waiehu, Hawaii. The airplane was registered to Mokulele Iki LLC., Kihei, Hawaii, and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91. The commercial pilot and his three passengers were not injured. Visual meteorological conditions prevailed and no flight plan was filed for the personal cross-country flight which originated from Honolulu, Hawaii, at 1530, with an intended destination of Kahului Airport, Kahului, Hawaii. The pilot reported to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) that while in cruise flight about 1,500 feet mean sea level, he noticed a slight hesitation in the engine. The pilot switched fuel tanks and verified the magneto and fuel selector positions. About 5 to 10 minutes later, the pilot noticed a second hesitation in the engine and performed the troubleshooting procedures a second time. Shortly thereafter, the engine began to run rough. The pilot noticed that the engine revolutions per minute (RPM) was fluctuating between 1,500 and 2,450, and the airplane would not maintain altitude. He initiated a forced landing to an open area, and during the landing roll the airplane struck various bushes and trees, before it came to rest in a nose low position. Examination of the airplane by a Federal Aviation Administration inspector revealed that the left wing and fuselage were structurally damaged. An unmeasured amount of fuel was located in both wing fuel tanks. The airplane was recovered to a secure location for further examination. A representative from the insurance company reported that during the wreckage recovery process, a Bell 206 helicopter was moving it from the accident site to the airport via an external long line operation. During the flight, the wreckage started spinning; the pilot jettisoned the external load cable attached to the airplane. Subsequently, the wreckage descended and impacted the water of the Pacific Ocean, just offshore from the accident site. The engine and one wing were recovered from the ocean waters about 2 days later. Examination of the Lycoming O-360-A4M, serial number L-31892-36A, by the NTSB IIC revealed that the engine remained attached to the engine mount structure; however, the mount structure was separated from the firewall. No evidence of any catastrophic mechanical malfunction was observed to the crankcase. All accessories remained attached to their respective mounts. The left and right magnetos, carburetor, vacuum pump, alternator, rocker box covers, exhaust, and top spark plugs were removed. The exhaust ports of each cylinder contained salt/sea water and sand-like material. The crankshaft would not rotate by hand using the propeller. The top spark plugs were wet and contained sand/dirt material. The left and right magneto drive shafts would not rotate by hand. Both magnetos exhibited severe corrosion. The carburetor exhibited severe corrosion. The mixture and throttle arms would not move by hand. The carburetor was disassembled. The interior of the float bowl exhibited white and green sludge-like substance, consistent with having been submerged in salt water. Both floats were intact and not damaged. The fuel screen was clogged with sand-like debris. Examination of the recovered engine revealed signatures consistent with salt water submersion. The reason for the loss of engine power was not determined.