Anyone owning an outboard-powered boat for long will need- or want – to replace their propeller. For most of us, that means doing the prop swap ourselves. The main reason props need replacement? Damage.
That floating log you didn’t see? The rock you found cutting across the shallows? At any speed, either of those chew-up a prop in no time.
The other reason people change a boat motor prop is to improve performance (here’s a handy calculator). Either way, knowing how to change a prop is a good skill and easy to learn. So let’s run through the basics.
What You Need
You’ll definitely need three things for your prop repair in the tool category: needle-nose pliers, a prop wrench (or socket set to fit the prop nut), and a chunk of wood. A short piece of 2″ x 4″ works fine. A flashlight and a sharp utility knife might come in useful, too. More about that later.
What else? You need the new prop, a replacement cotter pin, waterproof grease, disposable gloves, and a few rags. Make sure the grease doesn’t contain graphite – graphite is a surefire way to cause galvanic corrosion.
A Word About Hubs
If you hit something hard enough to damage the boat propeller severely, the odds are you’ll need to replace the hub while you’re at it. How do you know? If you had to idle home, your hub needs replacing. That’s the bad news. The good news is the hub saved your driveshaft. And almost all outboards built in the last 25 years have easy-to-replace hubs.
Many boaters keep spare outboard boat props and hub kits as standard boating equipment. You can swap them both out and be on your way in no time. It’s a simple boat repair.
Changing a Boat Motor Prop
First, tilt the outboard up, so it’s at a comfortable height. Then, using the needle-nose pliers, straighten out the cotter pin that runs through the castellated prop nut and pull it out. That goes in the trash.
Next, wedge the block of 2′ x 4″ between the cavitation plate and the prop blades. That keeps the prop from turning while loosening the prop nut with the prop wrench or socket.
Now, take off the prop nut and washer and set those aside. Now pull off the prop. Props usually slide right off. If your prop hasn’t been changed for years, you may need to tap it on the backside using a hammer and the 2″ x 4″ (for protection).
Take off the thrust washer – that should slide right off. Clean off the splined shaft with a rag. Check for any damage or wear, and cut away any fishing line you see.
Now, grease the spline, then reverse the process: thrust washer, new prop, prop nut, and cotter pin. And you’re done!
New Prop: 15 Minutes
Now you know how easy replacing modern outboard boat motor props is. So the next time you need to replace your propeller, you’ll be back on the water in no time!
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