Tractor Tugs - Innovation and Espionage

The Henry Foss at Work

"In the early 1920's, a University of Washington aeronautical engineering professor named Dr. Kirsten took out a patent on a totally new form of marine propulsion. Unlike a standard  propeller, Dr. Kirsten's model looked something like an eggbeater because it had six flat blades attached to a turntable arrangement, and the blades protruded straight down from the hull. The turntable spun, and direction of the boat and its speed were determined by the position, or pitch, of the blades."

This new propulsion unit allowed a boat to accelerate quickly, stop immediately, turn 360 degrees, and move almost sideways. It was enough to grab the attention of the Boeing Company, which partnered with Dr. Kirsten in the development of his propulsion system. But it was considered too revolutionary at the time to attract customers, and with the Great Depression and its aftermath in the 1930's, Dr. Kirsten's designs all but disappeared. Except in Germany.

Nazi leaders had learned of Dr. Kirsten's designs and after stealing them, put them to use during World War II on more than 100 minesweepers, aircraft carriers, seaplane tenders, and even self-propelled cranes. 

Toward the end of the war, US troops captured plans and parts of the propellers in Germany, and these then formed the basis for more research in the US after the war. A 135 foot German minesweeper was also captured and delivered to the United States, even though it was not designed as an open ocean-going vessel. Even though it encountered extremely rough seas, it made the crossing, and its skipper said that without the cycloidal propeller's added maneuverability, it wouldn't have made it safely.

Today, this type of propeller is common worldwide.  Workboats of all sizes use it or its near relative, the Z-drive. They have many advantages. There is no risk of stalling the engine or of steering failure. Extremely maneuverable and powerful, one tractor tug can do the work of two conventional ones. They can steer ships moving at speeds of up to 10 knots. In a sad twist of fate, Dr. Kirsten's patent had expired before success of his design really ever took hold, so he never profited financially from his idea.

In the Puget Sound, there are several tractor tugs in use: the Wendell Foss, Henry Foss, Andrew Foss, and Arthur Foss, all built by Tacoma Boatbuilding. The pilothouses have 360-degree visibility.

What was originally an American invention, stolen by Germany, only to be stolen back again, is alive and well on our Puget Sound, aiding large ships as they negotiate the its narrow waterways.

A big thanks to Archie Satterfield and his book, West Coast Workboats, for such a helpful and detailed account of tractor tug history.