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Black Dog Propellers uses Prop Scan technology to optically scan props, taking thousands of calculations related to the pitch and blade, down to one thousandth of an inch, to determine the surface profile of the blade and identify pitch imbalance and position. Computer profiling identifies the most efficient tolerance band and creates a map of isolated imbalances along each blade. Then, highly skilled technicians hammer and block the blade into balance. “We have the ability to put a design on each blade,” King explains. “We can pick up anywhere between eight and 12 percent in fuel efficiency, eliminate all propeller-induced vibration, and even decrease overall maintenance just by figuring out where the pitch balance is off.” As Thomas hammers the blade, it’s clear this is a delicate process. “He’s making it look way too easy,” says the shop’s finisher Rick Smit. “An experienced technician knows where to block and where to hit.” Placing the propeller back on the Prop Scan, Thomas’s work has already paid off. An immediate scan of each of the four blades shows the tolerance band tightening on the computer screen. And this is not just a lucky strike. “We go above and beyond ISO standards,” King explains. “The closer the blades are in tolerance to each other, the more

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efficiently your boat will run. Just imagine trying to drive your car with four different-sized tires on it.” Thomas pulls out a pencil and divider and starts to chart the dead center point on each blade to make sure each one is in proper position. Using the PropScan technology, he realizes that the dead center point has a deviation of up to two inches in track on each blade. King says that it’s not a great idea to trust that your props are good to go straight from the manufacturer. “When props are cast, they’re victims of the original cast. The weight can be up to seriously differ between blades, which will affect the shaft all the way to the engine. They’ll shake your teeth out.” Moving the propeller to the Dynamic Balancing Machine, Smit begins to spin the blade at high speed, measuring at what rotation and how many grams the prop is out of balance. “We’re getting there,” Smit says. Perfectionists. Black Dog Propellers performs scans and analyses on propellers for no charge. Considering the costs of annual maintenance, and what a tighter tolerance can do for the fuel efficiency of your ride, we have to recommend that as well. “We can take a prop out of the box and make it better, or we can bring it right back to specifications after significant use.” September 2015 35

PropTalk Magazine September 2015  

Chesapeake Bay Boating