Captain conquers engine puzzler
From Ocean Navigator #116 September/October 2001
On its return, the vessel's captain, Don Treworgy, was puzzled about mysterious shutdowns his diesel engine was suffering. It occurred typically, he wrote in email from the schooner to his home office, when the vessel was pitching heavily in rough seas, more specifically, when the vessel was pointing downward on the face of a steep wave.
Suspecting fuel flow problems, Treworgy changed out filters and found they were cleaner than they were after regularly scheduled changes, times when the engine was running fine. He ruled out dirty fuel for the same reason; the filters would be clogged worse than ever in this event.
"I listened for a long time to the rhythm of the change in rpm and noticed that the engine stalled when the boat pitched in the steep seas. It occurred to me that the water in the long exhaust pipe could be sloshing forward and aft with the deep pitches, thus creating back pressure when the water rushed into the silencers," he wrote. "The engine has an air supply blower which is very sensitive to back pressure, and we have maxed the pressure under the best of circumstances with such a long exhaust run and two silencers in line. For example, when there is too much water in the exhaust line the engine won't start, especially in cooler weather. Draining the water out of the line leads to the engine starting right away. Even a dirty air intake filter affects the starting of the engine."
Treworgy apparently solved the problem or at least figured out why it was happening: "Sure enough, when conditions were smoother, and I cleaned the air intake filter this afternoon, the engine ran smoothly. So it would seem that the unusual circumstances of running the engine under high rpm load (rather than just charging batteries) while the boat was pitching caused the loss of power."
He pointed out that the vessel was just clearing the north wall of the Gulf Stream at the time and was just over 200 miles from Watch Hill, RI., where the crew arrived two days later.