It’s one thing to haul a boat out of the water periodically to remove encrusted marine life from the hull and propeller, but today’s high-performance engines call for high-tech methods to balance and tune propellers for maximum efficiency.
Two companies use computers to fix boat propellers: Hale MRI and Prop Scan, an Australian propeller inspection system with a number of independently owned shops. Here in the U.S., one such Prop Scan shop is AccuTech Marine Propeller, Inc., of North Hampton, New Hampshire, owned by Larry Kindberg.
Kindberg says he “backed into the high-tech propeller repair business” when he couldn’t find anyone to fix his propeller after his charter fishing boat ran aground. He found Prop Scan on the Internet, took his propeller to a shop that used the system, and was so thrilled with the difference in his vessel’s efficiency, he became interested in the technology.
“This whole concept of using computers to tailor boat propellers really intrigued me, especially after I had it done to my own boat — it made all the difference in the world — and what I found out is that the repair of boat propellers is very basic. It’s like what a blacksmith does.”
Eventually he established his own business, using the computerized Prop Scan propeller assessment system. He’s at the shop from 7 a.m. every day.
Both the MRI and Prop Scan systems are alike, Kindberg said. “We want to know our customers’ boats as well as they do, so we can reach optimum efficiency.” Optimum efficiency in this sense refers to propellers being re-manufactured or modified to extreme accuracy.
“With computers,” Kindberg said, “we can see the accuracy of each blade down to a thousandth of an inch. We can also see the actual contour to a thousandth of an inch and can correct defects by bending metal to fix the blade using hammers or hydraulic machinery. The repair is very basic. We bend metal, we repair it, we weld it, we grind it, and we make it work. The computer helps us see what the design of the propeller is. We are just high-tech blacksmiths.”
Casting propellers, Kindberg said, is a matter of taking sand and mixing it with resin so it can harden, then taking a pattern of a propeller and sticking it in the wet, resin-y sand. Once the impression or mold is complete, molten bronze is poured into the form. When the bronze cools, it’s taken out of the mold, polished and machined into its final shape. New propellers straight from the factory, Kindberg said, may not be very efficient.
As an example, he took a hypothetical propeller with three blades. Theoretically the pitch of the propeller should be a 20-inch pitch (pitch is how far the propeller will move forward in one revolution). In theory, a 20-inch pitch propeller should move the vessel forward 20 inches for each full revolution of the blade. But in reality the propeller may move the boat forward only 18 inches because it also has to push the weight of the boat. This loss of two inches of pitch is referred to as “slippage,” and it occurs in propellers for many different reasons. The boat may be too heavy for the propeller, one blade could be at a different pitch from the others, or the entire propeller may be inaccurate. “It doesn’t take very much to affect the efficiency of a propeller,” Kindberg said. “Just because you have a new boat or propeller doesn`t mean it runs right.”
Donald Dewsnap of New Castle, NH, got dramatic results on his 37-foot Bertram, which has large, 550-hp diesel engines. Dewsnap’s propellers were way out of tune. He took them to Kindberg, who did the computerized assessment of the situation. The Prop Scan computer allows the technician to see the accuracy of the pitch of each blade. The pitch of Dewsnap’s propeller was 28 inches, his rpm was 1900, and his speed had been 22 mph. With reconditioned and tuned propellers from Kindberg, Dewsnap was able to achieve the correct engine rpm, the engines synchronized properly, and his speed increased to 28 mph.
Kindberg explained that a propeller is like an airplane wing. The propeller’s job is to move a boat through water by creating suction on the back side of the blade and thrust, or pressure, on the face of the blade, the side that pushes the water.
The computer also allows the technician to see the actual contour of a propeller blade to the accuracy of one-thousandth of an inch. Once the blade contour is corrected, efficiency increases, fuel consumption decreases and speed improves. In other words, Kindberg said, “fine tuning improves the efficiency of the propeller, and this improves the efficiency of the boat.” The final benefit, he said, is total elimination of all propeller-induced vibration.
One satisfied customer, lobsterman and lobsterboat racer Ira Guptil of Jonesport said, “I love the propeller. I think it’s phenomenal.” He explained that three-bladed propellers classically have more vibration than four-bladed propellers. Most lobster boats run four-bladers. “The way that [Kindberg’s] guys tune the propellers, they’re a cut above.” Guptil said he’s experienced absolutely no vibration and stated, “You wouldn’t know there was a propeller on board.”
John Hutchins, of Downeast Boats & Composites in Penobscot uses AccuTech propellers for his Northern Bay 38 lobsterboats.
Of his experience in dealing with Kindberg, Hutchins said, “I’ve never dealt with anyone as careful and professional with propellers as Larry. In my book, he’s a guru.” Hutchins said Kindberg takes the guesswork out of propeller repair. He said all Prop Scan facilities have to meet certain specifications, but that Kindberg takes it one step farther. Hutchins said Kindberg has given him information he’s never gotten any other place. “He has a tremendous amount of data in his computer. Up until I used Larry, it’s been more of a guessing game.”
Lobsterman Leroy Bridges, of Deer Isle, who said, simply, “I’m very pleased with the performance. It’s very smooth. It seems to be everything it was bragged-up to be.” For more information, go to www.accutechmarine.com.