Sharrow Props Give Grady-White Freedom 307 a Big Boost

Sharrow Marine’s innovative continuous blade propellers have consistently proven their superiority to conventional three and four blade propellers in tests conducted by Sharrow and independent companies — including BoatTEST.com. The results from a recent Sharrow test of a Grady-White Freedom 307 powered with twin 300-hp Yamaha outboards are typical.

The test was first run with the Yamaha’s propped with standard stainless steel 3-blade 15.5” x 17” propellers. The team then swapped these propellers with a pair of Sharrow Marine 15.5” x 17” TrueAdvance stainless steel propellers.

As the chart shows, the Sharrow propellers produce a significant advantage in fuel economy starting as low as 10 mph, primarily because the Sharrow’s plane the boat more quickly. At 30 mph, a speed common in offshore runs in rolling seas, the Sharrow propellers had a 17 percent advantage, delivering 1.74 mpg combined. The reduced fuel use is not only an economical advantage but also significantly extends the safe range of the boat. 

Prop efficiency is a measure of how effective a propeller is in turning rotary motion into forward propulsion. It’s common for standard propellers not to approach maximum efficiency until they get near wide open throttle. That was the case with the test propellers, which got to the 90 percent range only at 5000 rpm and above. On the other hand, the Sharrows jumped to 90 percent at 3000 rpm and peaked at 94% at just 4000 rpm, staying there to wide open throttle. 

The advance rate of a marine propeller is another measure of efficiency. A 15.5” prop at speed typically moves forward about 15.5” per revolution and that’s what the stock props did in this case, maxing at 15.3” at 5500 rpm. The Sharrows reached an advance rate of 15.2 at 3000 rpm and exceeded the design pitch at higher rpm, up to 16.0 at WOT.

Note that the Sharrow propellers, though the same designated pitch as the traditional 3-blade SS propellers, were faster at every given rpm above 2000. They were also faster at top end, where they reached 48.5 mph, even though the motors turned slightly less rpm — a clear indication of better advance rate and better use of the available horsepower with the Sharrows. 

More speed at lower rpm also allows the motors to be run at a slightly slower rate for good performance, reducing wear on the engines.

Users also report that Sharrow propellers produce less noise and vibration and give much more positive control in reverse and at docking speeds.