How do I know if my prop is bad?

How do I know if my prop is bad or if maybe my lower shaft is tweaked?


  • The only time you should have to change your boat prop is if you've damaged it or compromised its structural integrity. Or if you want to change the pitch to alter percormance. If your boat is sluggish, or has an unnatural vibration take a closer look at the prop for damage. You can also spin it freely and listen for any damage in the lower shaft housing. Take a look and see if it spins straight. The smallest bend can lead to much worse damage to the bottom end if it is ran at higher rpm's

  • @StevieRyder If you feel that your prop shaft is bent you will notice a new vibration that should be fairly significant or you will be able to stand behind the prop and spin it to see. If you have physical obvious damage to your prop, its always a good idea to have it checked just to ensure there was no further damage that may end up costing you much more down the road.

    Bad Prop Symptoms

    A lot of signs to take into account to verify you’ve got a bad prop or the wrong prop. 

    The Wrong Prop Pitch

    Prop pitch is the distance the blades move forward every rotation. If your prop’s pitch is too low, the engine may run higher than the recommended WOT rpm, leading to engine damage. If the prop’s pitch is on the high side, the motor will run below the recommended WOT range. This makes the boat feel sluggish and could harm the gearbox. 

    Propeller Damage

    Prop damage happens a lot and can be caused by many different factors. 

    Cracks or nicks, corrosion, warping, worn blades, strikes causing unbalance. Some damage is repairable and some props can be restored. 

    Mismatched Boat Prop

    Having the wrong-sized boat propeller can lead to engine problems that end up costing much more than replacing the prop with a correct one. A few things to look for that may indicate a mismatched prop: Is the boat laggy or hard to get onto a plane, Is the boat over or under-revving at top speed, is the engine consuming too much fuel? 

    If you take these things into consideration, you’ll be able to tell if you have a bad prop, or the wrong prop for your boat. 

  • If you have a feeling that your prop shaft is bent you can test it with a micrometer gauge. They sell some that clamp to the trim tab and it rests on your prop shaft. As you turn the prop shaft, it will read the difference in the micrometer gauge and let you know if your shaft is straight or not. This might eliminate some of your variables.

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