Hot Boat,
September 1996

Perfect Pitch
AeroStar Enters the Shiftable Performance Propeller Market.
by Bob Brown

AeroStar's Power Pitch® Pro is the product of more than eight years of engineering, testing and evaluation.

It's the ultimate dream of every hot-boater: one propeller and optimum all-around performance. The dilemma is as old as the outboard motor itself. You basically have three propeller choices: less pitch for more low-end punch, more pitch for maximum W.O.T. top speed or an in-between compromise pitch that delivers adequate performance throughout the rpm range. About six years ago, the marine industry saw its first shiftable two-speed propeller. It was a break-through innovation that caught the attention of performance boaters everywhere. Since then, several additional brands of shifting props have been introduced with varying degrees of success.
The newest entries into this marketplace, and easily the most intriguing, are the Power Pitch®; Pro and Switch Blade®; models, designed and manufactured by AeroStar Marine Corporation of Spokane, Washington. This is a sister company to Aerostar Aircraft - makers of the fastest twin-prop aircraft in the world. According to AeroStar Marine general manager Greg Speer, development of this new line of shiftable propellers consumed over eight years of engineering, testing and evaluation.
From a purely aesthetic viewpoint, the AeroStar propeller is an impressive piece of work. The internal hub mechanism, which executes the shift function, appears engineered and constructed with all the thoughtfulness and care so identified with the aircraft industry. Blade and hub configuration are likewise flawless, indicating that extensive study and research was done in creating this new adjustable stainless-steel propeller.
Although the internal hub mechanism looks complicated, the actual use and manipulation of the AeroStar prop couldn't be more simple. The manufacturer called it a "self-contained, bolt-on automatic marine transmission." It starts at relatively low rpm as a lower-pitch prop and then, as rpm and boat speed increases, shifts automatically to a higher pitch by adjusting the position of the three blades. The rpm shift point is controlled via a click-stop twist ring located just behind the prop nuts. No tools are necessary to make an adjustment; simply twist clockwise to increase when the shift point occurs or reverse the direction to delay it. Once the most comfortable shift point is determined, you should never have to touch it again. Also remember, this prop shifts down when you decelerate as well as up when accelerating.
The advantages of having two props in one is obvious. You have more bottom-end power when the prop pitch is less, and you enjoye the benefits (greater efficiency) of more pitch at faster on-plane cruising speeds. In many ways, its is like having a two-speed marine transmission built into your propeller. In theory, it sounds great. What boaters have been wary about in the past, however, is both reliability and actual performance.
From the reliability side of the equation, AeroStar has a confident answer: a three-year limited warranty against any mechanical failures (not related to obvious prop abuse, i.e. rocks, logs, stumps, etc.). As for performance, that can only be determined by trying the prop on a boat, which we did, in fact, on two very different boats.
Our first test candidate was a 20.8-foot Lavey Craft Sebring Mod-VP style tunnel with a 2.5 Mercury outboard (about 240 hp). This boat was fitted with a 26-pitch (there is six inches of pitch range built into the prop so it went from 20 to 26 pitch) AeroStar Switch Blade® three blade (the model designation for an outboard prop). In the past, the best speed this boat has seen is 76 to 78 mph at 6,500 rpm with a light load. The AeroStar ran right at that level with a 77-mph reading at 6,500 rpm, but the real difference was notedin the low range and midrange power and improved load carrying ability. Previously, the boat did not pull skiers with its conventional performance prop. With the AeroStar, deep water starts with a 250-pound slalom skier and carrying over 500 pounds of passengers was a breeze. Using moderate throttle acceleration, the AeroStar shifted at approximately 4,500 rpm (the 20-pitch mode) to 3,500 rpm (the 26-pitch mode). Under full throttle acceleration, the Merc wound out to 7,000 rpm and then settled in at 5,800 rpm after the shift point.
Our other evaluation boat was an Eliminator 250 Eagle XP bowrider (with a stepped-vee bottom) with a MerCruiser 454 MPI (385 pshp) and Bravo One stern drive (1.5:1 gear ratio). The AeroStar prop of choice here was a 24-pitch Power Pitch® Pro. We soon learned that we were a little too conservative in our choice since the engine easily touched the rev limiter at 5,150 rpm, so our top speed reading of 67 mph (radar) was a bit understated. However, our acceleration times from zero to 20, 30, 40, 50 and 60 mph were outstanding showing anywhere from a 30% to 40% improvement in elapsed time over the standard conventional prop.
Driving the Aerostar props truly did give the feeling that the boat was equipped with an automatic two-speed transmission. There's no question that low-end power was enhanced with the initial lower-pitch range. And although it's impossible to generalize about the top-speed characteristics of all boats, it appears that AeroStar has the performance side of the market will covered.
At the present AeroStar offers both outboard and sterndrive propeller models (all three blades) ranging from 17 to 28 pitch, available in one-inch increments. As long as the motor brand has a large style gearcase, AeroStar makes a hub and spline combination to fit it; and according to the warranty information, engines up to 400 hp may be accommodated. If this appears to be the performance cure-all that your particular boat has been looking for, expect to pay approximately $849.00 (suggested list retail) for the medicine.

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