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PIRANHA COMPOSITE OUR TOP CHOICE IN OUTBOARD PROP SHOOT-OUT

It seems everyone, including boat dealers, mechanics and friends, has an opinion when it comes to what kind of propeller works best. And this possibly explains why Powerboat Reports receives numerous inquireies from reader about prop selection.

Common questions: Aluminum or stainless? What about four blades? Can you really trust a plastic propeller? To answer with firm, conclusive findings, we needed to test all of these types of props on the same platform. And that's what we did.

WHAT WE TESTED

We wanted to cover the same range of propellers that the consumer encounters in the marketplace. These days, that includes props made of different materials, with a varying number of blades and sizes - even blades that are interchangeable for adjustment of pitch.

We chose five propellers to match against the three-blade stainless steel Yamaha prop (14-1/4" x 19"), which came with our test boat.

Our test boat was a 3,600-pound 1998 Grady-White 223 Dual Console, powered by a 1998 Yamaha 225 TXRW Saltwater Series II outboard. We launched our boat in a freshwater lake (Waquaquet Lake in Barnstable, MA) to eliminate the variable of current and therefore maximize the accuracy of our test readings.

These are the propellers we chose:

  • Two propellers from Michigan Wheel: a three-blade stainless-steel that measured 14.25"x 17.9" and a three-blade aluminum tha tmeasured 14.25" x 18.8".
  • A 14.25" x 17" four-blade stainless steel by PowerTech Marine of Shreveport, LA
  • Two composite nylon-fiberglass propellers (with replaceable blades) measuring 14" x 19" three-blade and a 14" x 18" four-blade from Piranha Propellers of San Luis Obispo, CA.

Boat owners may have also encountered another composite propeller on the market, Comprop. The Lenexa, KS, company declined to participate because our platform was too large for a Comprop to perform up to its potential, according to company president Tom Cray. Comprop does not recommend its propellers for boats larger than 21' or mor ethan 3,000 pounds.

HOW WE TESTED

Motor trim was the same for all propellers - set for optimum speed at each rpm test. On this boat, it meant raising the motor as far as possible short of ventilating the propeller, which minimizes the hull's wetted surface by raising the bow out of the water. Using our trim/tilt gauge, we made sure the motor trim was the same throughout the rpm spectrum for each propeller test.

Our course was east and west on the lake. Moderate wind and calm water was present during each trial.

Our performance data collection included readings for fuel consumption and mileage, speed, range and acceleration. The latter was accomplished by clocking the boat's time-to-plane. We also noted differences in maneuverablility and handling. To arrive at our conclusion, we analyzed the pros and cons of this performance data and weighed it against each prop's price and physical characteristics.

While we did record the wide-open speeds each propeller delivered, open speeds each propeller delivered, those readings did not play a role in our final recommendations. Most of our readers do not run their boats at WOT that much, sensibly opting to operate at cruising speeds. Running an engine primarily at high RPM will result in faster engine wear and shorter engine life.

PIRANHA COMPOSITES (3-BLADE: $144; 4-BLADE: $170)

Both the three - and four - blade Piranha composites are advertised as making stadnard aluminum propellers "a thing of the past for recreational boaters," only because you can replace blades on site if damaged.

We put this claim to the test by inadvertently chewing up the Piranha four-blade propeller while powering our testboat onto its trailer. The manufacturer sent four new blades. We put them on, and the prop worked fine.

We also encountered a mishap while testing the three-blade - we hit alog on the way back to the launch ramp, which sheared a blade in half. We got home fine at 1500 rpm. If this had been a badly bent aluminum prop, the resulting vibrations would have been greater and made getting home a lot slower. We concluded it's better tp have tha blade shear off than bend, if only froma "get-home" perspective.

Vibration levels for both three- and four-blade Piranhas were at least as low as the metal props, and the acceleration time was 3.9 seconds for each, also comparable to the stainless steel props. Backing response was on a par, too. Our only complaint: The instructions provided were porr, failing to walk you through the assembly process. The company should have improved directions available by summer's end, says president Brad Stahl.

BOTTOM LINE: These props were a nice suprise. We can easily recommend them as spares on a boat like ours, or even as a primary prop as long as spare blades are on board.

If operating extensively in unknown waters or shallow waters with a rocky bottom, we'd definately choose the composite prop over a stainless steel or aluminum prop since damage potential to the gear case would be greatly reduced. The composite simply shreds when it hits a rock, while a stainless prop may absorb the trauma and transmit it through the gear case. An aluminum prop offers more give, but not as much as plastic.

MICHIGAN THREE-BLADE ALUMINUM ($155)

Our single aluminum prop performed well but was a step slower than the stainless props, falling behind a couple of knots in the higher rpm ranges; it was also the slowest to accelerate by nearly half a second.

The Yamaha outboard managed to swing the aluminum about 100 rpm faster than the others, probably due to a combination of lighter weight and less effective pitch at a high rpm (compared to the stainless props) and less rotational drag (than the composites).

This prop backed well, no different than the stainless three-blades, and produced low vibrations level across the spectrum.

BOTTOM LINE: Like the Piranha, its price is attractive and its performance is comparable to the stainless steel wheels. This would be our second choice behind the Piranha three-blade for a primary propeller for this boat.

MICHIGAN THREE-BLADED STAINLESS-STEEL ($380)

This prop was a solid performer across the board, edging out out the aluminum and composites and nearly matching the other stainless steel wheels. At 3.8 seconds time-to-plane, it produced strong acceleration, and like the four-blade stainless steel propeller, vibration levels were very low. Along with the three-blade Yamaha prop, it backed the best.

BOTTOM LINE: If we wanted the durability and better performance of a stainless prop, we'd lean toward this prop. It performed comparably to the Yamaha and retails for $80 less.

POWERTECH FOUR-BLADE

STAINLESS-STEEL ($597)

This prop was a solid performer, turning in some surprisingly impressive mid-range and top-end speeds. Acceleration was fast, just 3.8 seconds on average during three time-to-plane tests. Vibration levels were minimal throughout the speed range. We noted about the same bite backing down compared to the three-blade metal props.

BOTTOM LINE: We'd describe this propeller as unassuming, almost making you forget it's there. It was second only to the Yamaha stainless three-blade in overall performance. But paying nearly $600 for this prop does not make much sense for this boat, since we got similar performance out of the less expensive Yamaha and Michigan stainless wheels.

We'd give this propeller more consideration if we expected to be cruising with a full boat or pulling water skiers. Its potential for power would have been demonstrated more if our test boat were heavier or carrying a full load. The four blades give it more blade area and therefore more bite in the water.

YAMAHA 3-BLADE STAINLESS ($457)

The best overall performer, the Yamaha squeeked out the fastest top end, 36.55 knots. It also handled admirably and showed little vibration.

BOTTOM LINE: For performance, you can't beat this porpeller. And don't forget, it's 2 years old. But we don't feel its very slight performance edge over the Michigan stainless is worth the extra $80.

PERFORMANCE VS. PRICE

We ranked wach prop according to its speed, fuel economy, mileage, and range at trolling speeds (1000 and 1500 rpm) and cruising speeds (35

We ranked wach prop according to its speed, fuel economy, mileage, and range at trolling speeds (1000 and 1500 rpm) and cruising speeds (35

We ranked wach prop according to its speed, fuel economy, mileage, and range at trolling speeds (1000 and 1500 rpm) and cruising speeds (35

"If the pitch, diameter and blade area are the same, propellers are going to behave pretty much the same regardless of material," says Dave Gerr, author or the "Propeller Handbook." But if those same propellers are called upon to move heavier loads, the material becomes more of a factor. The aluminum and composite props would flex more than the stainless props, enabling the latter to better maintain power and speed. Also, the power advantage of the four blades should also be more evident simply because their greater blade area is pushing more water than the three-blade props.

Let's look at the data:

SPEED. There's no noticable difference between the stainless and plastic/aluminum props in speed at trolling rpm (about a half a knot at 1000 rpm and barely 1 knot at 1500 rpm). The gap widens at cruising speed, with a 4-knot variance between the best and worst performers at 3500 rpm and a 5-knot difference at 4000 rpm.

But look who is the best- the composite props, delivering the most speed at both cruising rpm ranges.

ACCELERATION. The three stainless props registered 3.8 seconds time to plane, which was only 0.1 second faster than the composite props and 0.4 seconds faster than the aluminum. The numbers are close. Even a nearly half second advantage is not that substantial. And most of our readers aren't concerned much with acceleration.

FUEL BURNED. The stainless props burned about 1/3 of a gloon to 1 gallon less per hour than the composite props at 1000 rpm. All props burned just over 3 gallons per hour at 1500 rpm, except the Piranha four-blade, which used nearly 4 gallons.

The compostites lagged behind at 3500 rpm, burning a full 2 gallons per hour more than the stainless steel Yamaha and about a gollon more per hour than the others, inlcuding the Michigan aluminum. The difference in numbers is simialr at 4000 rpm, although the PowerTech joins the Piranha as the least efficient of the group.

MILEAGE. At trolling speeds, the stainless props show an advantage over the aluminum and plastic props, with the Yamaha getting about one-half nautical mile per gallon more than the Michigan aluminum.

The PowerTech gets slightly more than 2.4 nautical miles per gallon at 3500 rpm; the others lag behind, getting from 2.1 to 2.2 nautical miles per gallon. At 4000, the stainless props hold only a .2 nmpg advantage over the aluminum and plastic wheels.

RANGE. The performance advantages of the stainless wheels are greatest at trolling speeds. Still, you'd have to do a lot of trolling to make up the difference in price between the two props.

With the Michigan stainless prop, it would cost you about $85 to troll 100 miles at 1000 rpm, and $132 to troll at the same speed and distance with the Michigan aluminum. (These numbers are bades on the use of 90% of the Grady's 92-gallon fuel tank, with gas at $2 per gallon.)

The stainless retails for $224 more than the aluminum. So at an annual gas savings of $47 with the stainless steel, you'd have to troll 500 nautical miles before you'd make up the $224 price difference. That's a lot of trolling, about five seasons worth if you average about 100 nautical miles per year.

At 3500, the Grady-White has a range of 201 nautical miles with the PowerTech, compared to 175 nautical miles with the Michigan aluminum or Piranha four-blade. (The difference equates to 15%). Interestingly, the Piranha three-blade has better range at 3500 than the Michigan stainless (181 vs. 176 nautical miles.)

At 4000, all three stainless wheels are able to travel 184 nautical miles, which equates to about a 10% advantage over the non-metal props.

PIRANHA AND ALUMINUM

OUR CHOICES

On this boat, you'd have to pay at least $200 more to gain the slight performance edge that the stainless wheels hold over the others. In our opinion, it's not worth it for this boat. Stainless will last longer than aluminum, better at withstanding contact with sand, rocks, and logs.

But that durability must be weighed against the increased vulnerability a stainless brings to a lower unit. A stainless won't bend like an aluminum or shred like a plastic prop upon impact with a solid object, therefore the chances of damaging the lower unit increases.

A stainless would be a stronger candidate if we were operating solely in familiar waters or waters with sandy bottoms, where the chances of introducing a traumatic blow to the prop would be less.

The three non-stainless steel props-the Michigan aluminum and the Piranha three- and four-blades-are all abou the same price. The Michigan aluminum holds a slight edge in overall performance, although the Piranha three-blade has excellent range at 3500 rpm. The composites are easier and a lot less expensive to repair or replace. It will likely cost at least $50 to repair a bent aluminum prop, and $155 for a new one. But you can get a replacement set of three or four Piranha composite blades for $16 or $22 (price depends on hub size). So, our top choice for this boat would be a Piranha. We'd choose the three-blade based on its better performance.

Still, we're a little leary of giving the Piranha our 100% endorsment because we don't have much longterm experience with plastic propellers. We'd feel more comfortable keeping the conventional aluminum prop around as a back-up. Also, replacing a propeller at sea-no matter what kind- is tricky. And since the Piranha has one more part (rear cap) that needs to be aligned on the shaft and is not assembled until the shaft nut is tight, it makes replacement at sea all that much more tricky.