Preliminary Sharrow Prop Testing on a 37’ Center Console

Recently, the Sovereign Boat Club, a division of BoatTEST, decided that it wanted its fully equipped 37’ (11.28 m), 14,000-lb. (6,363 kg.) center console to be able to go 150 miles off the New Jersey shore this summer for big-game fishing over the canyons and return in a single day. Further, we wanted to have enough time over the fishing grounds to make the trip worth the time and money.

Mission Impossible

Unfortunately, that is a “Mission Impossible” with the boat’s standard Yamaha Saltwater Series II 15” x 21” (38.1 cm x 53.34 cm) props. With them, the boat’s greatest planing range was 301 nautical miles with a 10% fuel reserve, going just 23.9 knots. At that speed it would take 6 hours to get out to the fishing grounds, leaving just 1 hour and 30 minutes over the fish before having to take the 6-hour trip back to dock by nightfall.

Clearly, we had to change a major element of the equation to make this a “mission possible.”  We needed the large boat because she is seaworthy and will hold a party of anglers in relative comfort. And we needed the triple F300 Yamaha outboards because they are as efficient as any engine on the market to propel this heavy boat. The only variable left was the props.

Are Sharrow Props the Solution?

Would fitting Sharrow props — which we know are more efficient — make a big enough difference to make this mission possible?

We called Greg Sharrow, the props’ inventor and CEO of Sharrow Marine, and he suggested that we buy a set of his MX-2 props that would be custom-made for our boat and power package. With the props, he said we would be able to optimize our fuel burn and our speed specifically for our boat and its intended mission.

Within 2 days, Sharrow shipped us three off-the-shelf prop sets that were all about 15” x 18” (38.1 cm x 45.72 cm), but with subtle differences that are possible when using CAD-CAM technology. We tested all the props and recorded the data. This is the first step in the process of creating a set of custom MX-2 props. 

Conventional Props

When boat owners select the geometry of a conventional prop, the pitch and diameter determine if the boat’s performance will excel at the low-end, mid-range or the top of the RPM range. In most cases, buyers of new boats and engines rarely specify their prop geometry and accept what the engine maker or boatbuilder provides.  In most cases, these props are a compromise, designed for generally good, all-around performance.  

Testing the New MX-2 Design Protocol and Data Collection

We used a Maretron DVR 100 data recorder for our tests so that data points can be accurately averaged. BoatTEST was able to provide Sharrow with this data that enables its software to zero-in on the optimal design for our specific application. As of this date, several sets of beta Sharrow props were tested on the boat over four days. The final MX-2 props are now in the design and manufacturing phase and it will take about 8 weeks for the finished products to arrive.

Sneak Peek at Preliminary Results

Even though the final testing of this boat with its custom-made Sharrow props is weeks away, the preliminary testing indicated some important attributes that are worth passing along.

#1: Planing RPM is Remarkable

Perhaps the most dramatic takeaway from our preliminary testing of the Sharrow props on the 370CC was the fact that she could solidly stay on plane at 2500 RPM. Planing speed on this boat was between 17 and 18 mph, and we recorded an average speed at 2500 RPM of 19.4 mph on reciprocal courses.  

With the conventional props, we recorded 12.3 mph at 2500 RPM, 15.1 at 3000 RPM and 27.5 at 3500 RPM. With the beta Sharrow props, we recorded 28.1 mph at 3000 RPM and 34.5 mph at 3500 RPM — 25% faster than the standard props.  

#2: Speed Retention When Turning

One problem characteristic of larger, beamy boats with a deadrise of more than 20-degrees is when they are thrown into a hard turn, the speed tends to fall off quickly. When we tested the 370CC with conventional props we found this to be the case. At cruising speeds of 35 and 40 mph entering a relatively hard — but safe — turn, the boat quickly lost speed and fell off plane, or nearly so, unless we added throttle during the maneuver.

With the Sharrow props, it responded more nimbly in turns and held its speed much better, dropping only a bit, but we did not have to add throttle to keep the boat solidly on plane. In turns, the 370CC felt like a smaller boat, according to two of our test captains.

#3: Backing Down

Virtually all props are designed to optimize performance going forward, so when backing down on a gamefish, or even docking, outboard performance can be feeble with standard props. On outboards and sterndrives, the exhaust is routed through the prop’s hub, which ventilates the water behind the prop. When in reverse, the exhaust is now in front of the prop, and that, together with the prop geometry, makes backing slow.

Because of the more advanced hydrodynamics and blade design, the Sharrow props shined when backing down, allowing the 370CC to go faster and turn with alacrity because they grip the water better.

#4: Less Vibration

At Greg Sharrow’s suggestion, we switched back to the conventional props after testing the Sharrow props all day to see if we could detect any difference in the smoothness of the ride. Once underway, there was a noticeable increase of vibration with the standard props. Testing this setup last also made the other attributes more noticeable. While this was a subjective observation, all the persons on the test boat agreed that vibration was noticeably reduced with the Sharrow props.

Custom-Made MX-2 Sharrow Props

We eagerly await the custom-made Sharrow props. From our preliminary testing, it seems fairly clear where we will see marked improvement from the beta props we tested. We’re told that a set of three of the MX-2 props will cost $13k, which is just 1.74% of the MSRP of $750,000 of the boat. Given its promise of greater range, handling enhancements, less vibration and possibly lower bow rise on some boat models, that seems like a small price to pay.

A lot of work and man-hours go into making a custom MX-2 Sharrow prop:

1. After ordering, a Sharrow tech arrives at the boat’s location and sea trials the boat with standard props and several sets of “benchmark” beta Sharrow props with which to collect data points.
2. These data points are fed into Sharrow software and a computer designs the props down to a tolerance of +/.003 of an inch.
3. This information is fed into a 3-D printing process that makes a wax plug for the prop.
4. That plug is then covered in a ceramic material and the number of investment casting molds required are made.
5. The stainless steel is poured into the molds, using the lost wax method, and the resulting product has ½” greater material than required.
6. The raw props are then put on a 5-axis router and are machined down to the +/- .003 spec required, precision which is more than 10 times greater than what is found on conventional props.
7. A Sharrow tech then travels to the boat, fits the props to the engines and tests the boat to make sure that the performance desired has been met.

Once the 37’ center console has been fitted with the finished MX-2 props, we will test the boat again and report on our findings.