Sharrow Props

Sharrow Props on a Robalo R302 Center Console — A Comparison

Captain’s Report 



The First Center Console Tested 

Last year, more than 35,000 new center consoles were sold of all sizes, making them the most popular fiberglass boats on the market. While we have tested four boats with Sharrow props over the years, this is the first center console. But that doesn’t mean Sharrow Marine hasn’t been testing and perfecting their revolutionary prop design on all manner and sizes of center consoles over the last three years.



Sharrow Marine has largely held off from independent 3rd party testing and the resulting publicity – and sales -- simply because it was unable to produce enough props to satisfy the demand, due to the incredibly time-consuming and difficult process required to make them. The result was the company could only produce a limited number.



Happily, earlier this year Yamaha and Sharrow Marine signed an agreement whereby Yamaha would cast Sharrow’s complicated props in its state-of-the-art foundry in Indiana. Further, Yamaha is also distributing the new props through its network of 2,200 dealers nationwide. Thanks to Yamaha, all boaters will now have a chance to own a Sharrow prop.

A Proxy for Center Consoles

Early this fall, we tested our first center console with Sharrow props. Because the boat tested was a Robalo R302, we think of it as a proxy for many other center consoles on the market.  Robalo is one of the largest selling CC brands, and by testing a 30-footer we can expect to see similar results from others below and above 30 feet (9.1 m).



We should hasten to point out that any comparison tests between Sharrow props and any other brand of conventional props, is simply comparing new technology with old technology, that hasn’t changed much since the 1830s. There is nothing wrong with the conventional props we test, as they are usually the best of their type.  

We commend Yamaha for being intellectually honest, by validating the development of a new technology, even though they didn’t invent it.  

sharrow mx-3 props

Recently Capt. Steve was able to test a pair of Sharrow MX-3 props that were designed specifically for Yamaha V-6 outboard engines.  Sharrow is offering props with 22 different pitches, both left and right hand. 

The Sweet Spot

Typically, outboard manufacturers prop their engines with “general-use” props that favor top speed, while maximizing mpg at about 3500 RPM.  If a boat is unusually heavy, or the owner only cares about top-end speed, then other props will usually be specified by the builder or dealer. 19” props are generally considered to be at the top of the sweet spot for a large number of center console boats, as they are a fair compromise among the three major prop performance parameters of hole shot, fuel economy and top speed.

The conventional props on the Robalo R302 test boat were stainless steel SWS II 15.25” x 19” (38.73 cm x 48.26 cm). The Sharrow props were 15.36” x 19” (39 cm x 48.26 cm).    

Getting on Plane

One of the most critical aspects of every center console’s performance is at what RPM the vessel gets on plane. It is here that the Sharrow prop’s performance is remarkable on most boats that we’ve tested. In the test we conducted on the Robalo R302, powered by twin V-6 Yamaha 300-hp engines, the Sharrow props showed significantly more thrust than standard props in the critical RPM range of 2500 to 4000.

In the chart below, it can be seen that the boat equipped with Sharrow props is nearly on plane at 2500 RPM and 15.4 mph. At 2700 RPM (see the green arrow at left), the boat is firmly on plane (typically about 18-20 mph for these types of boats). And, at 3000 RPM, the vessel was recorded going 25.4 mph. 

With the conventional stainless steel props, the boat was not able to climb over its bow wave at 3000 RPM, and did not get on plane until about 3400 RPM (green arrow at right).

MPH by RPM

The center console hit 20 mph at 2700 RPM, but when propelled with the standard wheels couldn’t reach 20 MPH until 3500 RPM.

Critical Point of Operation. Just as an airplane must reach a certain speed before it can take flight, so too, must a powerboat reach a certain speed before it can get on plane and level out. Further, just like an airplane, the thrust required for “take-off” depends on the weight of the craft. The greater the number of people on a boat, the more thrust is required to raise the boat up on plane.

Zeroing-in on the speed chart above, we see that at 3000 RPM the Robalo R302 goes 25.7 mph --over 10.4 mph, or 69% -- faster with the Sharrow props than with the conventional ones. This occurs because of the greater thrust produced by the Sharrow props. Further, the Sharrow props also raise the stern slightly, which helps keep the bow down. 

Bow Rise Danger. We all experienced excessive bow rise 20 years ago when builders were switching from 2-stroke engines to 4-stroke on the same hulls.  Since 4-stroke engines have considerably less torque in the low RPM range, they struggled to get on plane. This can be an important safety consideration on some boats. 

R302 Sharrow Props

The Robalo R302 had minimum bow rise with the Sharrow Props.

The Importance of Planning Quickly

Who among us has not suffered the embarrassment in front of friends invited aboard, when the boat struggled to get on plane, and only did so with the engines loudly racing? Still worse, is the amount of bow rise which often obscures the horizon, restricting visibility, thus creating an unsafe few seconds of operation.

There are several important reasons why getting on plane quickly is important – and most revolve around safety. When a boat is struggling to get on plane, the operator has difficulty controlling the vessel as it can hunt from side to side, as it tries to climb its bow wave.

This is where novice operators can get into trouble by either slowly accelerating – which only prolongs the squirrely control – or, by slamming the hammer down with the result that the boat bursts forward leaving passengers with white knuckles, and possibly rushing up faster than anticipated on another boat or obstruction.

Sharrow MX-3 Prop

The conventional prop at left and the Sharrow MX-3 at right, which was specifically designed for Yamaha V-6 engines.

Cruising Speed Comparison

One of the most remarkable aspects of the Sharrow prop is the fact that it got this center console on plane at 2700 RPM, while the boat was still wallowing along at 11 or 12 mph, at that RPM with the standard props. 

At 3000 RPM, the R302 was shooting along at more than 25 mph, but with old technology props she could make only 13.8 mph.  It is at this point that the Sharrows are 86% faster.  This remarkable 11.9 mph speed difference is held to 3500 RPM where the Sharrows went 32.2 mph. The standard props were just getting solidly on plane at that RPM.

In fact, the Sharrow props were faster than conventional ones at all RPM settings except one – WOT.  Here the Sharrow props were .2 mph slower.  

R302

Center consoles constitute the largest category of fiberglass boats sold in the U.S. Their owners are typically the most demanding when it comes to boat performance. Above, the Robalo R302 on the way out to the testing grounds.

Sharrow props

Sharrow props are now being cast in Yamaha’s state-of-the-art foundry facility. Because of their thin blades, they are difficult to cast.

MPG by MPH

The red line represents the performance of the conventional 15.25 x 19 props, and the blue line is that of the Sharrow 15.36 x 19 props. Data points are miles per gallon (MPG) across the mph range. To be read: at 25.4 mph, the boat with Sharrow props got 1.8 mpg, 29% better than the conventional props at the same speed.

Much Greater Fuel Efficiency

The raison d’etre for Sharrow props is improved prop efficiency, resulting in fuel savings. In the chart seen above based on our test data we can see that the Sharrow props get more miles per gallon (MPG) than the conventional props at all speeds, except at WOT.  

Cruising Speed Efficiency. For a boat such as the Robalo R302 center console, cruising speeds are generally considered to be from 25 mph to 40 mph, depending on sea state, and how much of a hurry the operator is in. Here we see MPG improvements ranging from 5% to 29% for the Sharrow props over the conventional units. 

High-Speed Operation. Most boat owners don’t run their boats at high speed for very long. This is simply because it is very expensive to do so, greatly reduces the boat’s range, is not good for the engines, and, depending on the sea state, can be very uncomfortable. It is here, in excess of 40 mph, that the conventional props come into their own, nearly matching or equaling Sharrow's MPG performance at WOT. 

 

Range in Statute Miles

The Sharrow props on the Robalo R302 had greater range than the old technology except from 8 to 10 mph and at WOT.

Range Matters

For offshore anglers, the name of the game is range. The improvement Sharrow props deliver at cruising speeds from 25 to 33 mph is significant, providing from 65 to 107 miles more than the conventional props.  Once over the fishing grounds and trolling, again the Sharrow props are more efficient at speeds under 8 mph.  

Advance Rate

The numbers by each of the data points are the number of inches the props move forward with each 360-degree rotation at each RPM setting.  Since both sets of props have a 19” inch pitch, moving forward 19” would be a 100% advance.

How is All of This Possible?

In previous reports we have discussed the virtual elimination of blade tip vortices, reduced cavitation and the fact that Sharrow pros have twice as many blades than conventional props.  But the “magic” of the revolutionary Sharrow design boils down to the props’ advance rate with every 360-degree revolution.  

If you have heard the term “prop slip” and didn’t quite know what it meant, the chart above will be instructive.  In our tests we have seen that Sharrow props simply advance further with every rotation than conventional props (aka old technology). In the chart above, the most dramatic example of this is at 3000 RPM where the conventional 19” props advance 8.5” for every revolution, while the Sharrow 19” pitch props advance 15.83” for each full rotation – nearly twice as far.  

Observations

There is a lot about the Sharrow prop that we haven’t mentioned in this report, but BoatTEST’s Director of Testing, Capt. Steve, covers some of it, such as boat handing, in the video. And there are still other benefits that we have yet to properly quantify, such as their drastic noise and vibration reduction. That will come soon.