On July 20, 1999, at 1710 central daylight time, a Piper PA-24-180, N6316P, was substantially damaged during a forced landing at Boscobel Airport, Boscobel, Wisconsin. The 14 CFR Part 91 flight had departed Reedsburg, Wisconsin, at 1650 CDT with Boscobel as the final destination airport. The airplane was abeam the runway numbers when the engine coughed once and then quit. The private pilot landed the airplane in the grass that paralleled the left side of the runway. The airplane went into a drainage ditch and was subsequently damaged. The pilot was not injured. Visual meteorological conditions prevailed and no flight plan was filed. The pilot reported that he had pulled on the carburetor heat when he was abeam the runway numbers. He reported the engine coughed and lost power, and he made an immediate turn to the runway. He checked to make sure the fuel pump was on. He tried to pump the throttle, but it had no effect. He reported he decided to land on the grass when he determined the airplane was going to land short of the runway. He reported that during landing rollout, the airplane crossed over a drainage ditch and impacted the far side of the ditch, substantially damaging the airplane. The pilot reported that he had pulled the power back to 20 inches of manifold pressure to slow down so he could lower the landing gear. He reported that he had flown with 20 inches of manifold pressure for approximately two minutes prior to pulling on the carburetor heat. The temperature and dew point spread of 80/70 degrees Fahrenheit put the airplane in the "moderate icing-glide power" range according to the Aviation Safety Bureau Transport Canada guide for favorable icing conditions. The airplane was inspected. The engine started and was run. No anomalies were noted.