How to Fix a Boat Motor Prop
Boat propellers are expensive and, sooner or later, most boat owners will have an encounter with an underwater stump, a floating log or a rock in a shallow spot that will leave their propeller bent and vibrating. Unless the propeller tears itself to pieces, the unhappy boater can usually return to the dock, but once the boat is tied up or trailered, the cost of repairing or replacing a prop can be daunting; even the small aluminum propellers used on outboard motors can cost more than $100 to replace. A bit of old-fashioned work might help avoid these costs.
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Things You'll Need
- Clean bucket
- 1 bag masonry concrete mix
- Undamaged propeller
- Steel file
- Rubber mallet
- Basic hand tools
Instructions
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Mix the concrete and pour the "mud" into the bucket until the bucket is almost full. Let the mix set for 15 minutes. Use an undamaged propeller of the same type that is currently on your boat. Cover the hub (but not the blades) of the good propeller with tape to exclude concrete from the shaft hole in the hub, then push the good prop into the mix, just far enough to make a full impression of the blades, centered in the bucket with the front of the propeller (the side nearest the motor) face down.
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Remove the good prop from the concrete before the concrete is fully set.
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File down any sharp, damaged edges on the bent prop. When the blades of a propeller hit underwater obstructions, like logs, they tend to fold up toward the hub; but when the blades hit a hard, sharp object underwater, like a rock, they will sustain sharp-edged cuts or tears whose edges may dig into the concrete mold or a hand.
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Set the damaged prop into the mold, face down. If the prop has been badly bent, it won't be flush with the surface of the mold, but line up the blades of the damaged prop as nearly as possible with the impression of the prop in the concrete.
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Hit the propeller with the mallet, beginning on the outer edges of the least damaged blade, nearest the hub, then working toward the tip and in toward the center of the blade. Hit this blade two or three times, working along the edges of the blade from hub to tip, then move to the next blade, repeating the hit-hit-hit-move, hit-hit-hit-move process until the propeller fits into the mold tightly.
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Tips & Warnings
Before the boating season begins, you can remove the prop from your own boat and make the mold as instructed, using your own (as-yet-undamaged) prop. After removing the prop from the concrete mix, rinse with detergent and running water. Use masonry concrete mix; other kinds will contain small rocks (aggregate) that will cause damage to the mold or to a propeller repaired in the mold.
Once the mold has set, it will be very heavy. If the mold must be moved, use a furniture dolly to move it.
