A bent prop usually shows itself as a new vibration, a change in top speed or engine rpm, or a boat that handles differently after hitting something. To confirm it, look along each blade for bends, curled edges and missing material, then check that every blade tip passes the same fixed point at the same distance as you turn the prop by hand. Always stop the engine, remove the key or kill-switch lanyard, and put the engine in neutral before touching the propeller.
Signs your prop is bent
- Vibration through the steering or hull that was not there before.
- Lower top speed, or higher or lower rpm at the same throttle.
- Poor hole shot or trouble getting on plane; see boat won’t get on plane.
- Visible damage: bent tips, curled edges, chips or cracks.
How to check a prop for bends
- Stop the engine, remove the key or lanyard, and shift to neutral.
- Look closely along each blade from the side and from the tip; compare the blades with each other.
- Set a fixed pointer, such as a block clamped to the skeg or a marker on the cavitation plate, just clear of one blade tip.
- Turn the prop slowly by hand and see whether each tip passes the pointer at the same distance. A tip that sits closer or further away is bent.
- Check the hub for slipping; see spun prop hub.
How to tell if the prop shaft is bent
With the prop removed, turn the shaft slowly and watch the shaft end or splines against a fixed point; any wobble suggests a bent shaft. A dial indicator gives an accurate runout reading. A shaft can bend in a hard strike even when the prop looks fine, and running with a bent shaft damages seals and bearings, so have it checked by a marine technician if you suspect it.
Repair or replace?
Prop shops can often straighten and refinish aluminum and stainless props, and bronze inboard props, if damage is limited. Badly bent, cracked or heavily worn props are usually replaced. Aluminum props bend more easily and can protect the lower unit in a strike; stainless props are stronger but pass more force to the drive. See stainless vs aluminum props.
Fit the right replacement
Match diameter, pitch, rotation and hub to your engine, and confirm the engine reaches its rated rpm range at wide-open throttle; see the propeller sizing guide, prop slip and 3 vs 4 blade props.
Props and tools we list
- Yamaha M/T Series stainless 3-blade prop, 15-1/8″ x 25: $1,088.67
- ACME 1235 14-1/2″ x 14-1/4″ LH boat prop: $832.49
- 18 inch DynaQuad 4 blade bronze prop: $1,318.49
- PropSmith 3.00 prop pusher puller: $942.99
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More guides: how to remove an inboard prop.
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