Marine Steam Engines: Determine True Horsepower Demand of a Workload

The S.S. Badger is a passenger and vehicle ferry that has been in service since 1953. Currently, she shuttles across Lake Michigan between Manitowoc, Wisconsin and Ludington, Michigan.  What makes her unique is this: she is the very last coal-burning steamship in service in North America.

Due mostly to environmental regulations, burning coal on the Great Lakes has become prohibitively expensive.  The owners, Lake Michigan Carferry Service, are investigating whether to replace the 60 year old coal-burning steam engines with modern engines.  But how much Power is needed from the new engines?  The old steam engines were rated (60 years ago) at 3500 Hp each, 7000 Hp total for the vessel.  Does the ship need all that Power?  How much Power does she use now during normal operation and the routine crossing of Lake Michigan?  These questions must be answered now, before the new engines are specified.

Binsfeld Engineering and OpDAQ Systems were hired to make live measurements of Torque, RPM & Power on the two propeller shafts while underway, using the TorqueTrak 10K instruments plus Op-Torq Field Test data acquisition system.  The results were quite interesting and exactly what Chief Engineer Chuck Cart had expected.  Normal Operating Power for the steam engines was about 1700 Hp per shaft, 3400 Hp total.  Max Power output of the engines was about 2500 Hp per shaft, 5000 Hp total.

Conclusion: 7000 Hp is not needed for the new engines. 5000 Hp will be more than sufficient.