Reconditioning a Propeller

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Keewaydin’s propeller prior to reconditioning (left). It may look OK, but in fact it was horribly out of balance. It came back from the shop with the boat’s name engraved on it (right), and the improvement in performance under power was remarkable

Keewaydin’s propeller prior to reconditioning (left). It may look OK, but in fact it was horribly out of balance. It came back from the shop with the boat’s name engraved on it (right), and the improvement in performance under power was remarkable

The original purchase survey for my Allied Seabreeze sloop Keewaydin included a note about the fixed three-bladed bronze propeller: “some cupping noticed on all blades.” One of the surveyor’s post-purchase recommendations was to have the prop reconditioned. That was a number of years ago, but I had studiously ignored the prop until last spring, when I finally decided to have it looked at.

I had heard about the benefits of computerized prop scans, so I sought out a local shop that uses this technology. Prop Scan, an Australian company, is a pioneer in the field and licenses its technology to approved shops worldwide. One of these is AccuTech Marine Propellers in Dover, New Hampshire. AccuTech’s president, Larry Kindberg, said they could do the work before I launched in late May and quoted me what I thought was a fair price.

A computer measures the prop’s blades, but it takes a bit of old-fashioned hammering to true them up again

A computer measures the prop’s blades, but it takes a bit of old-fashioned hammering to true them up again

But first I had to remove the prop, last taken off the boat at least 15 years ago. I borrowed a rugged prop puller made by Walter Machine and went to work. The aperture for the prop made for a tight fit, but eventually I got the puller set up correctly and began to tighten the nuts. Just as I was wondering if the project was doomed to failure, I heard a crack and the prop released from the shaft neat as could be. It was a challenge finding just the right arrangement of blade and rudder angles to open the aperture enough to allow the prop to slip off, but eventually I had a three-blade prop resting in my hands.

Once in the shop, the AccuTech team put my prop on its Prop Scan machine and made careful measurements across each blade. Larry’s comment, “this prop is a complete mess,” was enough to convince me that I had made the right decision. None of the blades showed a matching, consistent pitch, they all had some cupping on the edges, and the prop itself was horribly out of balance. These factors all contributed to poor performance, including vibration, below-spec engine performance, and lower boat speed and handling characteristics.

The graph at the top shows how far out of whack the three blades on my prop were in relation to each other. The bottom graph shows their relationship after reconditioning

The graph at the top shows how far out of whack the three blades on my prop were in relation to each other. Thegraph on the left shows their relationship after reconditioning

After several days (spring is a busy time for any prop shop, and AccuTech is no different), I retrieved a beautiful, shiny like-new propeller. The boat’s name had even been engraved on one of the blades. AccuTech had gone through several steps with my prop—measuring, “adjusting” the blades until they matched each other (this involved a lot of noisy hammering), and then measuring again until its shape was perfect.

Installing the prop was pretty straightforward—no grease, just a couple of measurements to ensure proper location on the shaft and then a good tightening of the prop nuts.

The results? Less vibration, a noticeable reduction in the boat’s tendency to pull to the left under power, higher engine RPMs, and an overall improvement of at least a half a knot at cruising speed. Although I wasn’t initially sure propeller reconditioning was worth the trouble on a cruising sailboat, I am now convinced of its value. A quality shop like AccuTech services all makes and types of props, for all types of commercial and recreational craft, including feathering props. If you’re not sure your prop is true, it’s well worth looking into having it reconditioned.

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