Nor-Tech 392 w/Quad Mercury 350s: Enertia Eco Props vs. Sharrow Props

Every week Sharrow Marine’s techs test a boat or two to see how its props perform in different applications. Having established its superiority with single and twin applications on monohulls and catamarans, on both fiberglass and aluminum boats, with both boat gas and diesel outboards, the company was curious to see how it props performed on quad installations.

Also, many more of the comparative tests that have been reported on by BoatTEST have been on Yamaha engines with Yamaha props. Ironically, the very first test we performed was on a 20’ boat powered by a 150-hp Mercury outboard engine with a Mercury prop.  With their 26” centers, and high horsepower, Mercury engines are the coin of the realm when it comes to quads.

Not only did Sharrow want to see how its props would perform on high-horsepower Mercury engine sin a quad configuration – but it also wanted a throw-down with Enertia Eco props, which to many people were the gold standard for props, when it came to fuel efficiency. 

Mercury’s Enertia Eco Prop

But first, a little background on the on the Enertia Eco prop. It was reportedly designed over the course of 18 months by Mercury Marine prop engineers lead by Roger Koepsel, one of the most respected prop engineers in the country.  The Mercury team used the latest CAD programs, and 3D printing to test and perfect their design before releasing this prop to the public in 2014.  

At the time it was heralded by some as “revolutionary” because it could demonstrate 10% improvements in fuel efficiency, something rarely achieved by any new prop.  Indeed, BoatTEST investigated the claims and found them to be true. Its captains noticed that Mercury-powered boats seemed to perform better than they had with the older designs.

Testing a Nor-Tec 392

The Nor-Tech 392 SuperFish measures 39’ LOA, has a 10’ beam and weighs 17,000 lbs., dry. (11.88 m x 3.04 m x 7,727 kgs.) The boat is powered by triple or quads, depending on the top speed wanted.  She’s built of fiberglass and Kevlar and designed to go fast and take the punishment. The test boat was powered by quad Mercury 350-HP engines with Enertia Eco 16” x 23” props intended for high speed.

The Sharrow props were 15.5” x 22” – shorter in both dimensions. 

All data published here was recorded by Sharrow Marine techs and supplied to Boat TEST for publication.

Because on the vaunted reputation of the Enertia Eco prop, Sharrow techs were eager to see how their brand would fare against this worthy opponent.  The numbers in the chart above tell the story. The Sharrow design was from 5% to 19% more fuel efficient above 15 mph – except for one very interesting data point.

At 35 mph the 16” x 23” the Enertia Eco props were .0077% more efficient than the Sharrow design.  Perhaps not without coincidence, it was precisely at 35 mph where the Enertia Eco prop was 10% better that its 4-blade stable mate in 2014. 

When we compare speed data between the two props, we see that even though the Enertia Eco prop was designed to be more fuel efficient at 3500 RPM, the Sharrow prop was 2.9 mph, or 8% faster at that mark.  Note that from 4500 to 5500 RPM the Enertia Eco prop was from .7 to 2.5 mph faster.  Nevertheless, the Sharrow prop won fastest WOT honors by 2.4 mph, or 3.8%.  

In this comparison test, the question everyone asks is, how can the Sharrow prop be both mostly faster and mostly more fuel efficient?  The answer lies in the chart below. 

Get a Grip

Because of the Sharrow loop prop design, it’s able to simply get a better “grip” on the water, and “slip” less.  With every 360-degree revolution of the prop, it advances farther than the conventional prop. At higher RPM the conventional props slip relatively little and are at their most efficient at those speeds.

Mercury outboards have made their reputation, almost since the beginning of the company, on having engines that went faster.  Both its engines and many of its props are designed for top speed, so it is not surprising that it is there that they perform best. But, when it comes to normal cruising speed fuel efficiency, the  numbers that Boat TEST has published has shown that the Sharrow prop design is hard to beat. 

But fuel efficiency is not their only attribute.  Increasingly, consumers a draw to them because of their quiet operation and better control when docking.  But those are other reports for another time.  

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