Advanced props, rudders provide new efficiencies below the waterline
Professional Mariner|December - January2021
It took a decade or two from the invention of the marine propeller in the 19th century for the technology to become widely accepted. Thereafter, adoption has been nearly universal, but progress toward improved efficiencies has come in fits and starts.
Alan R. Earls

Now, though, a combination of factors — ranging from advances in computer numerical control (CNC) machining and modeling software to plain old ingenuity — have been speeding developments for propellers as well as for their stablemate, the unglamorous rudder.

A particularly interesting innovation in propulsion recently emerged from U.S.-based Sharrow Marine, which offers a new propeller technology that so far has been adopted primarily in the recreational market, but also should find a ready place aboard workboats, ferries and other commercial vessels.

The design was invented by Gregory Sharrow and subsequently developed by Sharrow Engineering LLC in Philadelphia. According to the company, 46 international patents have been filed related to the design, and 24 patents have been awarded in the United States, Japan, Canada, Australia, Europe (14 countries), Taiwan, China, and South Korea.

A key claim in the U.S. patent abstract is that the Sharrow propeller has “a means for creating fluid flow in a non-axial direction and redirecting it in an axial direction.” In other words, the centrifugal flow created as a byproduct of creating thrust is largely captured and redirected by employing the Sharrow design, which uses blades that resemble a slightly twisted loop rather than a curved paddle. That unique shape helps explain the company’s claims of improved performance and efficiency.

Translating tech gains into savings

To tap the full savings potential of improved propellers and rudders, you need advanced and flexible components farther up the drive train, especially in an era of evolving power sources.

Gary Aucoin, president and general manager of Schottel’s U.S. office in Houma, La., said one of the more forward-looking developments in the sector is his company’s response to the hybrid trend. In particular, Schottel is targeting workboats that have low engine loads during as much as 90 percent of their operation and therefore would have a duty cycle appropriate for hybrid technology. Those cycles tend to be less than optimally efficient, leading to increased pollution and high relative fuel consumption.

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