A short walk that Greg Sharrow took in 2012 may have led to one of the biggest technological leaps in propeller design in many years.
“I was trying to solve the problem of reducing unwanted noise from drones when filming live music productions when the idea of the Sharrow propeller and what makes it work came to me in a flash while walking my dog,” he says. “Although we did end up making a quieter drone prop, I realized this idea would have a much larger impact on the marine industry, so that became our focus.”
Now the CEO of Sharrow Marine, Sharrow says the source of the drone’s noise was the propeller tips that created vortices. The same phenomenon occurs on airplane wingtips, which is why most commercial planes have winglets: upturned additions at the end of a wing that disrupt vortices and enhance performance and fuel economy. Sharrow’s fix was to use similar engineering to eliminate the propeller blade tip. He looped the blade back to the hub.
While the concept seems simple, putting it into production required years and millions of dollars in research and development. In 2013, Sharrow reached out to the University of Michigan’s Marine Hydrodynamics Laboratory for help testing his designs. Sharrow Marine’s own research team consisted of engineers with more than 150 years of combined experience in the aeronautical, marine and aerospace industries.
Miniature-scale props were utilized. To better visualize the water-flow dynamics of each design, a 12-stream dye system was put in place. A high-speed camera (750 frames per second) captured the results. And computer-aided design analyzed various elements.
For third-party validation of the performance of the aluminum Sharrow MX-1 prop, a weeklong comparison against two conventional stainless props was conducted. A 20-foot Bayliner bowrider with a Mercury 150 FourStroke was used as the test platform.
For accuracy, test data was recorded on a Maretron VDR100, and fuel-flow information was taken from the engine’s ECU. One of the most significant advantages of the MX-1 over the other two props was its ability to put the boat on plane at just 2,700 rpm, compared to 3,700 rpm for stainless prop 1 and 3,400 rpm for stainless prop 2. Normally, when a propeller is faster to plane it’s slower at cruise and top speeds, but the opposite occurred during the test. At 4,000 rpm, prop 1 pushed the Bayliner to 27.7 mph, prop 2 to 27.4 mph and the MX-1 to 32.5 mph.
However, the Sharrow prop’s best attributes might be in other areas, including reducing noise and vibration. Although the Sharrow prop pushed the Bayliner to the highest top speed at 48 mph (vs. 47 mph for prop 1 and 44.9 mph for prop 2), it yielded the lowest decibel reading, which was surprising because higher speeds create more noise. At wide-open throttle, the MX-1 registered 87 dBA, while props 1 and 2 reached 90 dBA and 91 dBA, respectively. Comparing fuel economy at cruise speed, the Sharrow achieved 4.6 mpg at 32.5 mph, compared to prop 1’s 4.2 mpg at 32.3 mph and prop 2’s 4.1 mpg at 32.1 mph.
Peter Truslow, CEO of MJM Yachts, has tested Sharrow props on the water. “I was taken by the beauty of the design and shocked by the performance,” Truslow says. “The boats I ran came on plane at lower speeds and ran significantly faster and more efficiently throughout the rpm range. I also noticed a big improvement in handling. The Sharrow props grip the water at higher trim and don’t cavitate in hard turns.”
Given that the prop’s design is new, it’s natural to wonder about repairs. All new props come with a one-year Sharrow Care warranty that covers damage. Owners can purchase up to four additional years of coverage and must send the props back to Sharrow Marine for the work, though the company is looking to establish regional repair centers.
The MX-1 won an NMMA Innovation Award at the Miami International Boat Show earlier this year. The judging panel saw this technology, which has been awarded 24 patents, as a significant development for everything from runabouts to supertankers.
However, Sharrow props have a higher price point than traditional models. The props are milled to order from solid blocks of metal using a five-axis CNC router, a process that doesn’t lend itself to mass production. The aluminum version of the 15-inch-diameter Sharrow for engines up to 450 hp retails for $4,500, and the stainless version is double that amount. (A similar-size stainless Mercury Max 5 prop retails for about $2,200). Sharrow says the stainless steel version yields slightly better performance than its aluminum counterpart because the looped blade design makes the aluminum version more rigid than standard aluminum props. n