Refurbishing My Grandfather's Boat Propeller

My grandfather’s old boat propeller needed some care. It had some buildup, had lost its shine and had some scars from a previous attempt at cleaning it up.

Scraping and 80 grit

I started by scraping away the barnacles and the calcium carbonate deposits they leave behind. Most of it is calcite, the same mineral that makes up limestone, and an important part of the carbon cycle.

I then did a quick 80 grit sanding by hand to knock down any remaining buildup and highest points. I noticed, and was told by my grandfather, that someone else had used an angle grinder to remove buildup at one point. This dug a bit deep into the propeller and removed too much material, leaving deep scratches.

I could have sanded the rest down further to even those marks out, but I chose not to. Removing too much material has more negatives than positives: I could end up making the prop less efficient by changing the blade shape, or I could make the balance worse by removing material unevenly. Better to leave them as they are.

At this point we had to end the day, so I went home and researched how to properly sand and restore a propeller because I hadn’t polished a prop before, and sometimes simple things can have important details. I learned about how important it is to maintain the designed edges and not to sharpen them too much, as well as tips for what types of sandpaper to use. Pretty straightforward.

Stepping through the grits

The next day I started with 120 grit on an orbital sander, which cleared off the oxidation and remaining buildup. I then did a quick round at 180 grit. It was nice to see what a big difference just these two rounds had done, but now the elbow grease had to come out, as this was the last grit that I had for the orbital sander.

I hand sanded everything at 240 and 400 grit. From what I read, 400 is sort of the limit where the performance gains really happen. Beyond that you’re past the point where it meaningfully reduces cavitation nucleation sites and pitting.

With that in mind, I only sanded with 800 grit on the outward facing side. I did this just to make it look extra nice.

Polishing

This is where hours of hand sanding pay off in just a few minutes of easy polishing.

Closing thoughts

The result was fantastic. I am happy with it. The deeper scratches are still visible, but I know it is in a better state than it was. It was fun to surprise my grandpa with this. Fishing with him throughout the years has been the source of many of my favorite memories. It is just the best, spending time with him and other family, getting to see the beautiful Norwegian fjords from the water, AND getting the freshest and highest quality fish and crab.