Mercury has gone back to the drawing board and designed a new prop to operate more efficiently in the realm where most of us spend the bulk of our running time -- at cruising speeds. It seems that most props are focusing on quick hole shots or maximizing top speed but those areas mean little to someone operating a center console on an hours-long run to the fishing grounds. That’s why a prop that focuses on cruising speed performance is so much more advantageous.
Mercury Enertia ECO Prop Captain's Report
The Mercury Enertia ECO Prop was designed to provide more efficiency at cruise speed and directly save on operating costs.
The all-new Mercury Enertia ECO prop was designed to provide better fuel economy in the cruising speed range of the performance envelope. It was manufactured using a proprietary X7 stainless steel alloy only available to Mercury. The strength of the X7 alloy allows for a progressive rake to each blade that delivers better bow lift. It is available in both left and right hand rotation and in three pitches: 19", 21", and 23” (.48 m, .53 m, and .58 m) -- all with a 16” (.41 m) diameter. A 17” (.43 m) propeller is also under development.
Given current gas prices, even a 10% improvement in fuel efficiency at cruising speeds can result in a significant annual savings. That is the mission of the new Enertia ECO prop.
The Enertia ECO prop is designed with a progressive rake that increases as the blade moves from the hub to the outer edge.
- Large Blade Area. There is much more blade area on the ECO prop than is typical of a 3-bladed prop. In fact, in our comparison we tested it against a 4-blade Revolution 4 prop. The extra blade area of the ECO prop means comparing to a 4 bladed propeller is the closest comparison in the market.
- Larger Diameter. Typically a 19” (.48 m) pitch prop is going to be anywhere from 14" to 15” (.36 m to .38 m) in diameter. What makes the ECO prop unique is it’s a full 16” (.41 m) in diameter. This means that we not only have a larger blade area, but we’re now taking full advantage of the largest propeller diameter that the gear case allows.
- Designed for High-Horsepower Boats. This prop was made specifically for boaters who typically make long runs offshore. The fishermen running big center consoles with big engines. We tested it in a Mako 284 CC with a pair of 300-hp Verados, right smack in the crosshairs of the target customer.
- Progressive Rake. As the eye moves from the inside of the blade up to the outer edge, there is an enhanced rake, or cupping, that can easily be seen. This gives better performance out of the hole, and also adds a bit of bowrise to the cruise attitude, which means less resistance, producing better performance and fuel economy.
- Fabricated with the X7 SS Alloy. X7 is a proprietary stainless steel alloy exclusive to Mercury and it’s what makes the ECO prop possible. It allowed the design team to create a prop with a larger diameter and a progressive rake while still delivering the strength needed for hard offshore use.
It is not often that we get to perform an "apples-to-apples" test, but this was one of those rare opportunities. In a matter of minutes we were able to change out the Mako's props and go back to testing in the same conditions and on the same boat.
The Mercury Enertia ECO prop test results.
The Mercury Revolution 4 prop test results.
Props for a Purpose. With a hard-working offshore boat, a typical propeller would be the Revolution 4 with a 19” pitch and four blades. This application wouldn’t typically be using the same propeller as the ECO prop. And that is why our comparison test is so enlightening.
Similarities. When we compare the surface area of the two props, we discover they are roughly the same because the Enertia ECO's blade size is larger than the Rev 4s four smaller blades. Thanks to ECO's larger diameter, the blade area is roughly equivalent. And there are some other similarities between the two props --
Our test platform is a typical one for the ECO prop’s target customer, a hard working offshore center console. In this case, the Mako 284 CC with a pair of 300-hp Verados.
- The Rev 4 is the 4-bladed cousin of the 3-bladed Tempest Plus prop; so comparing it to a 3-bladed prop isn’t a stretch.
- Both the Enertia ECO and the Rev 4 are designed for hard offshore use.
- Both are made for high horsepower engines: 150-hp and up.
- Both are offered with the Performance Vent System. This system has holes in the sides of the hub that can be fitted with vent inserts of varying sizes depending on the application. This allows air into the prop stream so it can spool up to speed quicker and with less resistance. This provides for better hole shots and quicker times to plane.
The Comparison Test
We tested the Mercury Enertia ECO prop on a Mako 284 Center Console with a test weight of just over 8,900 lbs. (4,048 kg). With a pair of 300-hp Mercury Verados turning the Rev 4 propellers we set out on our first test to establish a benchmark.
Between tests, the Rev 4 props are changed over to the ECO props under the watchful eye of Captain Steve. We knew he wasn’t going to get his hands dirty.
Here’s a look at the standard Rev 4, to the left, and the new Enertia ECO prop, to the right, in the middle of the changeover process. Both props are made of stainless steel.
Here we can see a marked improvement in the bow rise as we come up on plane. With the Rev 4 we had a 14-degree bow rise (left), and with the ECO she got on plane with only 9-degrees (right). However, when running at cruise speeds the bow will be slightly higher with the ECO prop providing less resistance and wetted surface.
- Top Speed Improved. Well, our top speed increased from 52.5 mph to 54.7 mph, that’s an improvement of 4.2% but there was little improvement in the fuel economy at wide open throttle.
- Hole Shot Improved. We also found an increase in hole shot, from 3.5 seconds to 3.4 seconds in time to plane. That’s an improvement of 2.9% but again… not the target of the Eco prop, so we’ll consider these two details as perks, but not reasons to switch props.
- Bow Rise Change.
It quickly became clear that to make a proper comparison, we needed to do so at fixed speeds rather than fixed rpm settings, as we usually test boats. That would be the only way to properly assess the improvements, or lack thereof, of the ECO Prop. We noted that at speeds the Rev 4 was slightly more fuel efficient than at most settings.
ECO Efficiency Takes Hold. At 2500 rpm the two props produced almost the same speed -- 13.5 for the Rev 4 and 13.6 for the ECO prop. Here we recorded a gph fuel burn for the ECO prop of 9.80, a full 1.0 gph better than the Rev 4 at 13.5 mph burning 10.8 gph -- or, a 9.3% fuel efficiency improvement.
Efficiency Grows with Speed. From that point right up to the speed and rpm ladder the Enertia ECO prop was significantly more fuel efficient than the Rev 4. At two typical cruise speeds, 30 mph and 35 mph, let’s see how each prop did--
30 mph Cruise. At a cruise speed of 30 mph our total fuel burn for both engines dropped from 19.4 gph with the Rev 4 props, to 15.8 gph with the Enertia ECO props. That’s in improvement of 18.6%.
35 mph Cruise. At 35 mph our total fuel burn dropped from 22.8 gph to 20.8 gph for an improvement of 8.9%.
The apogee of the ECO efficiency curve appears to be at about 30 mph. As we approached WOT speeds of 54.7 mph for the ECO prop and 52.5 for the Rev 4, the disparity in fuel efficiency once again narrowed. At WOT, the ECO prop's advantage was simply +2.2 mph and only a very slight advantage in fuel consumption.
At 30 mph the Enertia ECO 3-blade props outperformed the Rev 4 four-blade props by an impressive 18.6% in fuel efficiency.
Time to Plane: Huge Improvement
- 0-20 mph. Our time to reach 20 mph went from 5.9 seconds with the Rev 4 to 3.9 seconds with the ECO. That translates to an improvement of 34%.
- 0-30 mph. The time to 30 mph went from 12.5 seconds to 7.5 seconds, an improvement of 40%.
22.7% in Greater Range
Greater fuel efficiency does not only result in money saved, but it also gives the boat far greater range. For example, at 30 mph our test boat will have a range with the Rev 4 prop of 317 statute miles. With the new ECO props, it will have 30 mph at a range of 389 statute miles for a 22.7% increase in range. (Calculated with a 228-gallon tank and a 10% fuel reserve.)
At 35 mph the Enertia ECO 3-blade prop was 8.9% more fuel efficient than the Rev 4 four-blade prop. The ECO also had the highest WOT speed at 54.7 mph compared to 52.5 mph for Rev 4. Even at WOT speed and going faster, the ECO prop was slightly more fuel efficient than the Rev 4.
At 35 mph the economy improved 8.8%. The higher we went, the less improvement there was. Staying at the mid-range showed the best improvement.
So What Have We Learned? Clearly, the low range shows little improvement, and the high range shows a little more, but not a significant savings. However, in the speed range where Mercury designed the new prop to perform, she came through with flying colors in our apples-to-apples test.
That means that our tests have indeed validated the goals of the Mercury Enertia ECO prop in saving boaters money by utilizing this higher efficiency prop. The more the boat gets used, the more money saved over the standard props -- and, we're talking real money here.
Bottom Line. For example, assuming fuel costs $5.00 per gallon (to keep the math simple), and the boat was run at 30 mph for 100 hours during a long season, the difference in fuel consumption would be 970 gal. - 790 gal. = 180 gal. 180 gallons x $5.00 = $900.
Greater Range. Many blue water fishermen we know carefully calculate the distance to the offshore canyons where they like to fish and often buy boats and engines based largely on the range of the boat. Now, these same fishermen will find themselves with a new set of options for simply the price of a couple of props.