The oscillating steam engine, built by John Penn & Sons, is located aboard the famed paddle steamer Diesbar. Diesbar is the second oldest of a fleet of nine paddle steamers in Dresden. What makes the Diesbar unique is its coal fueled engine and single deck design. The John Penn and Sons engine that runs the steamer is the oldest operational marine steam engine in the world. It has been in operation for over 165 years.
Built in 1841 by John Penn & Sons of Greenwich, England, the Diesbar’s engine is a two-cylinder oscillating steam engine. The oscillatory feature allows for the incorporation of fewer parts in comparison with other steam engines of the era. This ultimately cut down on total material and helped to address two major engine design issues that plagued the time period, size and weight.
John Penn & Sons Oscillating Steam Engine - Diesbar CrankshaftThe John Penn engine is put into motion when steam from the boiler enters the cylinders of the engine. The steam enters the cylinders through the outboard trunnions and exhausts through the inboard ones. The third cylinder is fixed and is used to maintain a partial vacuum in the condenser. The crankshaft then turns two paddles with feathering blades. The feathering blades turn twice as fast as fixed, radial blades and thus are twice as efficient.
While this particular John Penn & Sons engine has resided above the Diesbar for 124 years, it was originally aboard the Bohemia, starting in 1841, and then the Stadt Meissen in 1857. The John Penn engine was both a unique design and major contributor to early steam engineering. The mere fact that the Diesbar’s engine has been operational for over 165 years speaks for the quality of the design and manufacturing engineering that went into John Penn & Sons engines.