Prop Repair and Selection

Prop Repair and Selection


By Mike Carey

I can remember the exact place and time it happened…

My wife and I were fishing Lake Wenatchee for sockeye in our brand new Thunderjet. The fishing had been good but the dogs were letting us know that they needed a shore break. I scanned the shoreline and found what looked like the perfect spot to ground the bow and let the dogs hop out. I eased the boat on to shore and gave a little throttle to nudge us solidly in place. Then I heard it. Grind grind, chip chip chip. I knew immediately that it was shallower than I thought and my brand new prop had gotten its first official ding. Darn it! I had been so careful up to that point. The damage wasn’t severe, but it was depressing seeing that shiny new prop scrapped and chipped up.

I imagine there are more than a few of us that have had this experience, or something similar to it. A chipped and bend prop is a normal part of boat ownership, I think. That said, chipped and bent props can cause some significant issues to your boat and motor performance. A damaged prop can keep your motor from its optimal RPM to horsepower ratio and cause cavitation. That prop can also send unwanted vibrations up through the whole motor, causing seals to breakdown and leak oil out and let water in causing further damage. In short, nothing much good can come from a damaged prop.
With that in mind, on my winter “to do” list was to visit a prop shop and learn more about getting my prop fixed and also seeing if the factory supplied prop was the right prop for my boat. I visited Precision Propeller Company in Spokane and spoke with owner Darren Prouty to get some answers. Darren is second generation prop expert, having started working in his dad’s shop at age eight. With over thirty years in the propeller business, he knows his craft.

Darren looked at my prop and noted the chips and told me that it would be a fairly easy fix, something his shop does on a regular basis with a one week turn around. However, he noted that the prop I brought in was more suited to a Mercury 115 HP motor versus the 150 HP motor I had. With that bit of surprising news, we had a discussion on the advantages of upgrading a prop for my boat and motor.

Darren talked about the difference between an aluminum prop and a stainless steel prop. He noted that aluminum props were thicker and more prone to cavitation issues. Stainless steel props are thinner, creating less drag. Aluminum props over time no longer measure the same pitch or diameter. The prop is the “governor” on the engine and it regulates RPMs. A full boat can cause issues that may not be seen on an empty, “out of the factory”, boat. Problems like coming up on plane easily can be the end result of a less than optimal prop. Aluminum props are also softer and wear much easier vs. stainless steel. Stainless props, being harder, have a “breakaway” inner sleeve so if you hit something, the sleeve is designed to break before your motor gear shaft does. Darren noted that I should see significant performance improvement with a stainless steel prop. He said that, in general, he didn’t have a favorite stainless steel prop brand. In his experience, the quality across brands is quite good. One nice thing that Darren offers his customers is to test run their new stainless steel props and report back with RPM to HP results. If the prop isn’t right, he’ll make the right adjustments so you do have the right prop. That’s a great company guarantee.

So, to summarize the main advantages of a stainless steel prop, you get a couple more MPH at a given RPM, faster acceleration to plane, and better durability. These are all very compelling reasons to upgrade your prop. One downside, besides the price, or maybe because of the price, is that stainless steel props are more prone to theft. Stainless steel props will run you about 2/3rds more in cost than aluminum. No one ever said boat ownership was without its risks.

After Darren’s explanation of props, I decided to get a stainless steel prop for my boat. I’m excited to see how the boat performs and will be sure to let you know in future reports the results. In the meanwhile, what about my damaged prop? Well, I do a lot of overnight trips in isolated areas and sleep in my boat. If I’m any distance from civilization or other anglers, I don’t want to have to rely on my kicker to bring me home if a break a prop. So I’m getting my aluminum prop repaired, and will have it in the boat for emergency prop replacement. It just makes good sense in my book to have a spare prop. Darren also produces a very nifty prop wrench which is designed to provide the proper torque to tighten your prop nut at just the right pressure, around 60-75 pounds of pressure. The wrench also has a locking and lifting device all on one wrench. Put it in the bag!
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