PowerStop! Reverse Thrust Propeller Offers Safety and Control

PowerTech!’s new PowerStop! reverse thrust propeller provides new levels of control without diminishing the boat’s overall performance.  This new design (patent pending) incorporates unique cupping on, both, leading and trailing edges to improve stopping, backing, and maneuvering performances. 

The PowerStop! is presently available in aluminum propellers for E-class motors, from 150-300 hp, and in 15.5” x 11”, 15.5” x 12”, and 15.5” x 13”. 

...To Four, or Not To Four...That is the Question

For many years, now, boaters have debated the question of 4-blade propellers versus 3-blades.  The traditional argument is that 4-blades are slow and 3-blades are fast, end of discussion.  Today, new trends in the marine marketplace, higher fuel prices, challenging economic times, and the like have all brought new concerns to the boating world.  Speed is, now, a much smaller part of the equation; while practical, real world performance becomes the consumers primary concern.  In this new modern age, the question arises anew, but this time, with a different answer. 

MYTH vs. LEGEND

In the beginning, the idea that 4-blades were slower than 3-blades was true to a certain extent, but that is because many of those 4-blades were not designed with speed in mind.  Instead, the few designs that were available were intended to cure handling issues such as ventilation, cornering blowout, motor elevation requirements, and holeshot issues.    Without many options in blade design, and very few of them truly intended to be particularly fast, the 4-blade got branded as slow, while their other performance benefits were largely dismissed.  By contrast, today’s 4-blade propeller designs have evolved into, both, all-purpose and highly specialized geometries.  These propellers can be tailored to, not only, address those traditional handling issues, but can also be tailored to improve a boat’s performance envelope, which can, in some cases, even include speed.

The increased blade area afforded by the addition of the fourth blade can provide increased water displacement capability, lift, and grip, as compared to the comparable     3-blade propeller.  In terms of actual boat performance, these characteristics can combine to enhance handling, holeshot, low-speed planning ability, cruise efficiency, fuel efficiency, load-carrying performance, big seas performance, following seas/down current performance, ventilation/cavitation resistance, motor elevation capability, etc.  In short, a 4-blade propeller can improve all those characteristics that make for practical, all-around boat performance.

So, why might a 4-blade generally be slower than its 3-blade counterpart?  To be honest, many 3-blade/4-blade speed comparisons are simply not fair. That’s because the respective propellers in question are simply different styles, designed with different purposes in mind—different diameters, rakes, cupping, and blade shapes.  If, however, for comparison purposes, we take two propellers, identical in design (blade shape, diameter, rake, cup, etc.) that is appropriate for a given application, and simply add a propeller blade, we get a truer representation of just where the difference lies.  The addition of the extra blade causes increased drag, which, in turn, requires more horsepower, in order to achieve the same rpm. Since the horsepower is limited, the rpms drop, and the speed will tend to drop with it.  This is why, when going from a 3-blade to a 4-blade, the pitch is dropped an inch, or more, in order to keep rpm parity.  It is this difference in pitch that causes any potential speed differential between the 3-blade and the 4.

As to any actual speed loss between the two, in many cases, it is actually quite small (generally 1-3 mph).  The reason is, although the 4-blade is one-inch lower in pitch, it runs more efficiently than its 3-blade competitor, allowing it to run closer to its theoretical speed than the 3-blade, thereby, effectively closing the gap presented by the pitch differential. 

TRENDY 4-BLADES

As the result of many of today’s trends in the marine marketplace, 4-blade propellers have become more popular than ever.  As fuel prices have risen, fuel efficiency and cruise efficiency have become prime concerns for boaters, and 4-blades can offer improvements to both.  Other trends in the marine industry, such as, the move toward 4-stroke motors with their heavier weights and higher numerical gear ratios, shallow-flats boats, tunnel boats and cat boats with their ventilation-prone running characteristics, ski-boats with their pulling requirements, heavier deep-V offshores with their big seas control requirements, can all benefit from the additional grip, lift, and efficiency of 4-blade propellers.  In short, 4-blade propellers have become almost indispensable in maximizing boat performance and customer satisfaction. 

Where customers were once resistant to the idea of a 4-blade propeller, we are actually finding that customers come to us asking if their applications will benefit from the use of a 4-blade propeller.  In many of these cases, the answer is a resounding, “yes.” 

DESIGNING THE SOLUTION

As we have learned more about what makes a propeller work and not work, and about how boats and motors perform and do not perform, we have designed propellers that address the inherent strengths AND weaknesses of each of these respective pieces of the puzzle.  These designs have become even more important as more and more specialized boat designs and motor trends have entered the marketplace and as new trends and economic challenges arise.  All that said, the most important part of the equation remains the customer’s performance expectation and satisfaction; so, the goal is to match the propeller to the boat, motor, AND the customer’s needs…as always, the right tool for the right job.

Marcus Clements
a.k.a., Funky Monkey from Maverick Boat Company's customer message forum at www.mbcboats.com

Speed has always been the foul temptress of the marine industry.  Everyone wants to go faster than they “bought,” and fuel has always been relatively cheap.  Global Positioning Sensors (GPS) made this all the more critical, as speed could, then, be measured to the tenth of a mile per hour.  At the same time, fuel mileage was rarely, if ever, a concern.  If speed is the foul temptress, then fuel efficiency has been the proverbial, red-headed stepchild…that is, until now. 

Soaring fuel prices have changed the very nature of much of the marine industry’s focus because their customer’s performance expectations have changed.  Customers who, once, wanted every scintilla of speed they could muster, are now looking to maximize their boat’s fuel efficiency and range, instead.  Just as with any aspect of boat performance, the propeller holds the key. 

The only reason a propeller-driven boat moves, at all, is because the propeller displaces (moves) water beneath the boat.  As luck (and physics) would have it, the hull of the boat and the water, together, are pretty slippery, so as the propeller displaces this water beneath the boat, the boat moves across the top of the water.  The more efficiently the propeller moves this water, the more efficiently the boat moves, which makes the motor’s job easier.  If the motor is working with less strain, it will use fuel more efficiently.

Granted, this is an oversimplification, but it does address the basics of what can be a very complicated scenario.  There are many other factors to consider, such as, does the boat require sternlift to offset a rearward bias in the center of gravity, or bowlift to reduce wetted surface area (friction), or is the inefficiency due to propeller slip (whether hull, motor elevation, or propeller geometry related).  Whether it is weight-, friction-, balance-, or grip-related, all of these issues can often times be addressed, to one degree, or another, just by changing a propeller. 

Whether an application’s fuel efficiency and range can be improved upon with a propeller really depends on just how well it is propped, initially.  In some instances, the boat is propped correctly and there is very little to be gained, while in others, the propeller is incorrect for the application and significant improvements can be found.  The degree to which this can be done will be highly dependent upon just what the boat/motor combination is lacking, and just HOW lacking it is. 

In one particular example, we were asked by an OEM boat manufacturer to address just such an inefficiency on a 32-foot performance cruiser with twin 250 hp 4-strokes.  The boat had an excessively high minimum plane speed (marginal plane below 4100 rpm), poor low-speed handling characteristics, excessively high fuel consumption, and excessive bowlift running the stock moderate-to-high rake 15 ½” x 17” 3-blades. 

In this case, it was determined that the boat was suffering from a rearward-biased center of gravity, and propellers without sufficient blade surface area.  In order to address this, we increased blade area by increasing the number of blades to four, utilized a propeller geometry with lower rake for more sternlift, and dropped the pitch one inch, to ensure that we allowed the motors to run in the heart of their torque band.  As a result, at the target rpm of 3500, the original 17” 3-blades ran 15 mph lightly loaded and 11 mph loaded, using 14.5 GPH.  At the same rpm, the 16” 4-blades ran 23 mph and 22 mph at the same respective loads, and used only 13.5 GPH.  As you might expect, the fuel range was similarly extended.  As icing on the cake, the tester’s comments on the boat’s improvement in “feel” were just as important to the manufacturer as the performance gains.  It’s a bit like redesigning the boat, without ever going back to the mold.  Now, this is an unusual case, and not one that will be repeated often, but it does give a very good example of what can, and sometimes does, happen just by changing propellers.

Whether you are interested in fuel mileage, speed, holeshot, handling, load-carrying, or what have you, it is critical to choose the right tool for the right job.  Just as the right prop can make a boat, the wrong prop can break it, so once you determine the aspects of performance that are most important to you, take the time to find the prop that best satisfies YOUR needs.