Installing a New Outboard Boat Propeller

Hey there! Replacing a boat propeller might seem like a daunting task at first, but with the right steps and a bit of care, it can be pretty straightforward. Let's dive into the process together. Remember, safety first, so let's ensure everything is set up correctly before we begin.

Safety Precautions

Before you get started, it’s crucial to prioritize your safety:

Engine Preparation:

Make sure your engine is in neutral and the ignition is either turned off or disconnected. This is to ensure that the engine won’t start accidentally while you're working, which could lead to serious injuries.

Thrust Washer Check:

Never install a propeller without a thrust washer in place. The thrust washer prevents direct contact between the propeller and the engine, avoiding potential damage. If you notice a tapered surface at the gear case end of the prop shaft, that means the thrust washer isn’t there. Sometimes, it might stick to the front of the propeller you just removed, so check there first.

Propeller Installation

Let’s walk through the installation step-by-step:

Step 1: Prepare the Prop Shaft

Inspect for Wear and Damage

Before you do anything else, take a close look at the prop shaft. Look for signs of wear, corrosion, or damage. Any imperfections can affect the installation and performance of the new propeller.


Remove any old grease, debris, or marine growth from the prop shaft. A clean shaft ensures better adhesion of new grease and a smoother installation process.


Apply marine-grade grease to the prop shaft splines. This lubrication helps the propeller slide on more easily and protects against corrosion caused by water and salt. Ensure the grease is evenly applied but not overdone; excess grease can attract debris.

Step 2: Installing the Thrust Washer

Positioning the Thrust Washer:

Slide the thrust washer onto the prop shaft. It’s crucial that the tapered side of the washer aligns with the taper on the shaft. This alignment is key to ensuring the propeller is properly balanced and mounted.

Checking for Fit:

Once in place, give the thrust washer a gentle wiggle to ensure it’s seated firmly and correctly. There shouldn’t be any play between the washer and the shaft.

Step 3: Mounting the Propeller

Propeller and Hub Assembly:

Carefully align the propeller with the hub assembly onto the greased prop shaft. Ensure that the propeller slides smoothly over the splines without forcing it. If it doesn’t fit easily, double-check the alignment and the cleanliness of the shaft and splines.

Installing the Tab Washer and Locking Nut:

Tab Washer Placement for Mercury Motors: After the propeller is in place, slide the tab washer onto the shaft end. This washer is critical as it locks into specific positions to prevent the nut from loosening.
Tightening the Nut for Mercury Motors: Screw the locking prop nut over the tab washer. Using a torque wrench, tighten the nut to the recommended torque, typically about 55 ft-lb. As you tighten, make sure the tab washer doesn’t spin separately from the nut, as this could mean it’s not seated properly.

Installing the Locking Nut and Cotter pin for All other Motors:

Tightening the Nut for all other Outboard Motors: Screw the locking prop Using a torque wrench, tighten the nut to the recommended torque, typically about 55 ft-lb.

Installing Cotter Pin: Make sure the hole for the cotter pin is visible through the castle nut. Place cotter pin through the hole and use needle nose pliers to bend each side of the cotter pin 90 degrees or more in opposite directions

Final Security: Depending on the design, secure the setup with a cotter pin or by bending the tabs of the tab washer into the grooves on the nut or spider washer. This step is crucial as it prevents the nut from loosening under vibration or reverse thrust.

Step 4: Final Adjustments and Checks

Propeller Free Movement:

With the engine still in neutral, manually rotate the propeller to ensure it moves freely. This check helps confirm that the installation is correct and there are no obstructions or misalignments.

Clearance Check:

As you rotate the propeller, watch for any potential strikes against the trim tab or anti-ventilation plate. These components should have a clear distance from the propeller blades to avoid damage and ensure efficient operation.


Trim Tab Interference:

If you notice the propeller hitting the trim tab, you might need to replace the trim tab with a specific type like the Quicksilver flat plate anode #76214A5. This part is designed to avoid interference and can be sourced by calling us.

By following these steps and keeping a keen eye on safety and correct placement, you’ll find that changing a boat propeller is a manageable task that ensures your boat performs at its best. Safe boating!


Replacing a boat propeller involves inherent risks, including but not limited to personal injury, damage to equipment, and improper boat operation. While the guidance provided aims to assist in the safe replacement of a propeller, it cannot cover all scenarios or anticipate every potential hazard.

By choosing to replace your boat's propeller, you acknowledge and assume all risks associated with these activities. It is highly recommended that you follow manufacturer-specific instructions, use appropriate tools, and adhere to safety protocols to mitigate risks. If you are unsure about any steps or procedures, consider seeking professional assistance. Neither the content provider nor any affiliated parties shall be held liable for any damages, injuries, or complications that may arise from the propeller replacement process. Use this guidance at your own risk.



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