June 21, 2008
High lift rudders enhance pusher tug's steering
Seeking to improve the steering of its 4,000 HP Columbia River pusher tug MV Clearwater, Shaver Transportation Company of Portland, Oregon, fitted two high-lift rudders designed and built by Deflector Marine Rudder of Naselle, Washington.
After six months use, Shaver has found the rudders perform as predicted, producing more turning force and markedly improved steering, which is especially valuable when pushing barge trains in the restricted channel and strong winds in the Columbia River Gorge.
According to Shaver's port engineer, Dennis Malloy, the Clearwater had recently been fitted with a new set of Kaplan propellers and nozzles. The change in waterflow across the plate rudders significantly reduced the rudder force, particularly at low power settings. Large trailing edge wedges were added to the rudders, but the Clearwater still had less maneuverability than before the nozzles were fitted
Malloy contacted Lowell Stambaugh at Deflector Marine Rudder, who has built high-lift rudders for many different applications. He designed a pair of foil-shaped high-lift rudders with articulating trailing-edge flaps that fit the tug's existing flanges, rudder stocks and rams. They are heavily built of zinc-primered steel with upper and lower flap actuator mechanisms that fence the water flow.
At small angles of helm, the Deflector rudders present a very streamlined low-resistance foil shape. At larger angles, the bull-nosed convex leading edges grab a larger percentage of the nozzle flow and re-vector it. Hard over, the rudder's cross-section delivers powerful stern-thrusting.
Stambaugh says he has demonstrated that his high-lift rudders develops at least twice the force of a conventional rudder, and can improve the efficiency and safety of most conventionally-powered working vessels.