The best thing a boater can do to ensure the integrity and performance of a boat’s propellers can happen in a grimy prop-tuning shop, but longer propeller life is something you can strive for every day. Here’s a list of the top four tips for keeping your propeller, or propellers, in top shape.
Maintaining your boat propeller
1. Longer propeller life begins with reading nautical charts.
Prop shops and professional prop tuners stay in business not because people want to eke out those last few MPH of performance from their boats, but because people hit things—a lot. The most frequent problem—and this is just the nature of boating—is running over things, running aground, hitting sand bars, rocks, and so on. I have heard stories about boaters from four different parts of the country who ran over a chain. Long story short, use your depth finder and charts—that's what they're there for.
2. Address Nicks and Scratches
Obviously, it doesn’t take much to damage a propeller. Many propellers on the market today—Mercruiser's Alpha- and Bravo-style drives, for example—are so thin at the leading edge and so finely tuned that even small debris in the water can cause scratches and nicks. And those nicks and scratches can develop into cracks.
So, every time you wash the boat, pull the prop off, grease the prop shaft, use what the manufacturer recommends for grease, and spray the propeller with some CRC 656. Visually look it over for any scratches, cracks and little nicks. If there are any nicks in it, it’s highly recommended to remove them with sandpaper or a file. If it’s a larger ding, consider getting it fixed professionally because nicks can turn into a crack over time.
How can a scratch turn into a crack? The answer lies in the loads a propeller endures and the amount of flexing it does during the course or regular use. Scratches are easy to see, particularly on polished propellers, but it can be difficult to distinguish between a crack and a scratch. Professional shops use Magnafluxing, which uses ultraviolet lighting, sensitive dyes and magnetic particles to identify cracks. For home use, Magnaflux also offers a Spotcheck kit, which runs about $70, which go-fast boaters can use to check for cracks right in their garage.
The Spotcheck kit doesn’t require UV lighting to highlight surface cracks. The kits come with complete instructions, but the short story goes like this. Clean your propellers and spray on the penetrating aerosol and wipe it off with the supplied cleaner. After that, you spray on a developer, which will cling any cracks the penetrant has located.
3. Cracks Require Professional Help
If you do find cracks, it’s time to turn it over to professionals. Depending on their severity, cracks can be repaired by welding them closed and refinishing them. Once a blade breaks, however, there is nothing you can do to repair it. It has crossed the threshold from propeller to paperweight. Time for a new wheel.
On the leading edges, a nick or two might not seem like much, but they truly diminish the performance of your propeller. Nicks on the leading edges cause more cavitation, create more drag and can even manifest in a vibration you can feel throughout the boat.
If you catch them in time, techs can fill in the nicks by building them up with a weld, then refinishing them to a polished finish.
4. Propeller Tuning
The way propellers are mass produced, it’s rare that any two propellers are the same, let alone two blades on the same propeller. A competent propeller shop can make all the blades the same dimensions, which is hugely beneficial in terms of performance.
They can match each blade, match the profiles and the cup for each blade. That procedure not only makes a propeller run truer, but it also makes for a better balanced propeller, because each blade does the same amount of work.
Now, go find those nav charts and stop hitting things.
For more on propeller maintenance, read:
- How to Change a Boat Propeller
- Understanding Propeller Pitch
- Which is Best: Aluminum or Stainless-Steel Boat Propellers?