Vessel Repair Receives Second Patent For Pacesetter Class Towboat
Vessel Repair announced that it has received a second patent on its Pacesetter class of inland towboats.
The first patent was for the hull design that combines a single chine with a double chine and arranges the two distinctly different hull forms into specific areas of the hybrid hull. (See WJ, May 24, 2021.) This takes advantage of the positive features of both while reducing the negative features, the Groves, Texas, shipyard said in an announcement.
The new patent is on the Pacesetter flanking rudders. The rudders are foiled or shaped blades, but only one side is foiled, creating an asymmetrical shape. The flat sides of the rudders are toed inboard to the shaft, like most flanking rudders; however, on the standard flanking rudders, the foil shape on the inboard side—even with toeing rudders—does not completely offset the outward foil taper. The distance between trailing edges is greater than the distance between the rudder stocks. The result is an opening effect from rudder stocks to the trailing edges. Water passing through this area slows to fill a larger area, and the pressure drops, the company said.
The asymmetrical-shaped rudders, with the flat surfaces toed in and with no offset for stocks, speed the water flow to the wheel and increase the water pressure instead of decreasing the flow and pressure, Vessel Repair said.
The propeller on a vessel is similar to a pump. Like any pump, the faster the flow and greater the inlet pressure, the greater the resulting thrust. Standard flanking rudders just forward of the propellers reduce efficiency, especially during long runs. However, asymmetrical flanking rudders are designed to increase flow to the propeller and increase efficiency.
Vessel Repair’s patented asymmetrical flanking rudders can not only eliminate standard flanking rudder inefficiency, but add efficiency to the propulsion system, giving them a dual purpose, the company said. The new rudders are equally balanced with the same length leading and trailing the rudder stock. The quadrant keyway is offset to position each rudder in the correct direction and amount. The rudder stocks are also double-keyed to allow each rudder to fit either inboard or outboard of the shaft. This allows for only one spare to fit in any position.
Both the hybrid chine and the asymmetrical flanking rudders were tested using a Computational Fluid Dynamic study, or C.F.D., with favorable results, and they are both included as standard features on all Pacesetter pushboats.
Vessel Repair has built eight Pacesetter vessels with patented hulls; the last three were also outfitted with the recently patented asymmetrical flanking rudders.