Plastic Propeller Test:
Piranha Holds Off Old Foe Plus Newcomer
The four-bladed Comprop's low price and excellent performance make it a worthy contender, but the Piranha three-blade allows you to change blades and pitch.
When it comes to performance, composite propellers can certainly hold their own when pitted against their stainless-steel and aluminum counterparts, we learned this lesson well in our last propeller comparison (July 2000). For example, the two plastic props tested (a three- and a four-blade from Piranha) actually pushed our 22' Grady-White test boat to a higher cruising speed, and subsequently better mileage, than two of the stainless steel wheels and one of the aluminum props tested.
The performance numbers led us to conclude that the plastic wheels from Piranha could indeed serve the Grady well as a primary propeller - better, perhaps, than the metal ones in our shallow, rocky waters: Composites protect the lower unit by shredding instead of transferring trauma through the gears upon impact with a hard object.
For various reasons, we were only able to obtain plastic props from Piranha for our test last year. This year, we've matched Piranha against an old foe - Comprop - and a newcomer, the Swedish-made ProPulse.
What We Tested
The Grady-White is too big and heavy for any of the Comprop propellers (they can only be used on boats under 21' and 3,000 lbs.), so we used another boat: The test platform this time around was our 20' 6" Neptune 212, powered with a 130-hp Honda four-stroke.
Using our engine's original stainless steel prop's pitch measurement of 15" as a baseline, we followed the instructions from each manufacturer to select the appropriate plastic wheels. We ended up testing four propellers: a three- and a four-blade from Piranha, a four-blade from ProPulse and a four-blade from Comprop (the latter two companies make four-blades exclusively). Although the pitches of each varied, our choices seemed to be right on the money since the Honda 130 with each of the four props tested achieved 5500 to 5600 rpm at wide open throttle - right in the middle of its operating range of 5000-6000 rpm.
The Piranhas consist of a center hub, a rear cap and the blades. The four-blade model does not require the original propeller's thrust washer because the aft section of its hub is beefed up with a 1/2"-thick brass washer. Piranha attaches a large red tag to the propeller to make sure the owner does not install the original thrust washer. It would be nice if the directions concurred with this warning. The installation instructions (on Page 2) tell you to reinstall your original thrust washer, which is incorrect, confirmed Piranha sales manager. The Piranha three-blade prop utilizes the original thrust washer.
The ProPulse's components, a rear hub section and ring, a slip gauge, a front hub and the blades' are held together with four stainless steel bolts that are tightened and loosened with the Allen wrench provided. A series of notches on the hub serves as a scale to adjust pitch. The larger mid-position mark represents the original pitch, which is stamped on the blade foot, and (+) plus and (-) minus signs let you know whether you're increasing or decreasing pitch.
Of course, the one-piece Comprop required no assembly and therefore was the easiest to install.
How We Tested/What We Tested For
Our analysis included recording speed and fuel consumption at cruising rpm ranges and at wide open throttle. We tried to get a handle on acceleration by measuring how quickly the boat reached 20 mph and 30 mph with each of the propellers. We used our boat's Standard Horizon fuel meter to record fuel usage (gallons per hour), and our fixed-mount Garmin 125 GPS to measure speed. This information is listed in the chart on Pages 10-11. We ran the boat through the same tests with the stainless steel propeller provided with the Honda.
We deliberately tried to chew up each propeller in the sand to make sure they worked at advertised. As we said, composite propeller blades are supposed to break or tear to avoid damaging the lower unit. We noted ease of assembly and installation and the clarity of the instructions. Back at the office, we gathered other pertinent data, including price and warranty information (see Page 10).
The Comprop and the Piranha three-blade outperformed the other two, holding a 1-2 knot advantage at 4000 and 4500 rpm. At wide open throttle, the Comprop and Piranha three-blade pushed the boat to nearly 28 and 29 knots, respectively, compared to the Piranha four-blade's 25.4 knots and the ProPulse's 26.5 knots. Acceleration numbers followed suit, with the Comprop and Piranha three-blade propelling the Neptune to 25 mph in 11.75 and 12.5 seconds, respectively. With the other two props, it took the boat a long time to get up on plane (achieved at about 15 mph) and reach the 20- and 25-mph marks. For instance, it took the Piranha-propped boat 7 seconds longer to reach 25 mph than the Comprop-propped boat.
In comparison with the stainless steel wheel, the Comprop and three-blade Piranha pushed the boat as fast - if not faster - at most rpm levels. The other two composites fared well against the stainless, as well. In fact, all four plastics reached 20 mph quicker that the stainless.
The composite propellers did indeed tear during our grounding test at the beach; the ProPulse was chewed up the worst, but all the blades on each of the propellers were damaged to the extent that they would have to be replaced.
Let's weigh the other pluses and minuses of each. The Comprop costs less than the other three, but its one-piece construction doesn't allow you to change blades or adjust pitch, meaning you have to buy another prop if you hit something and ruin a blade[s].
While it's the most expensive of the group, the ProPulse offers the greatest flexibility: The pitch of our test model could be adjusted from 16" to 20" simply by rotating the hub left or right. You have to change the blades on the Piranhas to adjust pitch.
The ProPulse's drawbacks? Changing blades takes slightly more work than the Piranhas, and it carries a 3-year hub warranty compared to the life-time coverage of the Piranha and Comprop wheels.
The Piranha's strengths are their simple and cheap blade replacement. The four-blade's lack of bite, or inability to quickly push the boat onto plane, proved to be its greatest drawback on this boat. The three-blade model did much better.
The Piranha four-blade and ProPulse's performance on this outboard on the boat lags too far behind the other two. Therefore, it comes down to either the Piranha three-blade or the Comprop four-blade. Both seem like good matches for our test boat. We'd give a very slight performance advantage to the Comprop, which gets the boat up and onto plane quicker than the Piranha. Prices are close, too ($100 for the Comprop and $116 for the Piranha).
We like the Comprop a lot. But its minimal acceleration and price advantages over the Piranha three-blade don't outweigh its lack of changeable blades, in our opinion. If you destroy a blade on the Comprop, you have to spend another $100 for a new prop, compared to spending $19 to replace a damaged blade on the Piranha.