Propeller vibration

[GreenLake]

I have a three bladed Kipawa propeller for my trolling motor and it's started to show strong vibrations. (Definitely not the "good vibrations"). Vibrations are strong enough that the shaft will not stay locked and the motor starts pointing sideways... makes me think that whatever the impalance is, it's not a simple question of weight imbalance - nylon isn't very heavy to begin with.

Also, no vibrations can be felt when the propeller runs in air.

Anybody ever have the same/similar problem and is there a remedy other than sending it back in?

[TIM WEBB]

Hey GL,

I bought one of those for my old troller (34#), and it vibrated right from the get go. Same as you say too: only in the water, not in the air. I chalked it up to worn seals/bearings/possibly bent shaft on the old motor. Has yours only started to vibrate after it's been on there awhile? Mine doesn't fit on the new troller (45#), so it's been relegated to my box of "stuff that didn't work but might at some point in the future" ...

[GreenLake]

Yep mine was fine for many seasons and suddenly showed this symptom. I think it happens when one of the blades gets bent a bit, and since you can't rest the motor w/o putting weight on the propeller (unless you have some kind of stand) I think I might have simply bent one of the blades. If it was weight difference in the blades, it would vibrate in air - if anything the propeller spins faster.

I placed the propeller on a flat surface (hub down) and compared the distance of the blades to the surface. That was not totally even, so I tried to bend the offending blades in the right direction. They look closer now. If they don't relax overnight, I'll try them tomorrow and see whether I got an improvement. I also sanded out a very miniscule nick in one of them (less than 1/16") just in case it contributed.

If this is not fixed, then I need to check whether the bending relaxed, and / or whether - even though the tips line up - the pitch of the blades differs.

[K.C. Walker]

Greenlake,

It doesn't seem to take much of a distortion in the blade to cause vibration. I look after our family boats at the summer place where a lot of different inexperienced drivers use the boats. We end up sending aluminum props to the prop shop on a somewhat regular basis. My observation is that even if the props get dinged without losing any material, they still vibrate. I don't think you can get plastic props reconditioned so I think you'll need a replacement if you want to totally eliminate vibration. I've tried filing props to try to even out dings without a great deal of success.

[GreenLake]

Well good news. I tried the motor today with the propeller manually "bent" as described in my post and the vibrations are gone. Not just "less" but it's like day and night. I motored for nearly 15 min today at high speed. To prevent future issues, I plan on knocking together a simple "stand" or propeller guard. Something that will keep the blades from taking weight when the motor is resting sideways.

[TIM WEBB]

Good to hear GL! Never even thought to check blade alignment when mine was on the old motor ... DOH!

'Course, my trollers have always lived on the transom, so they've never been set down in such a way as to put any weight on the prop. But, my Kipawa vibrated right out of the box, so it could have been defective from the factory, or been damaged in transit ...

Just for kicks tho, I'd like to check the prop as you have: by "hub down", do you mean the end facing towards the motor (forward) or the aft end?

[GreenLake]

Aft end. The tips of the blades then almost touch the surface.

[TIM WEBB]

Well, just took another look at mine: placed it on the flattest surface I could find (tempered glass dining room table top), and sure enough, two blades almost touched the surface, and one was about 3/16" up. Bent it down, and it was close, but then over a few minutes, it *did* "rebound" back up. Did you use any heat or anything to aid in your bending effort? Looking at it again, I also see that the part of the hub that faces the motor is not really round, but kind of "oblong" in the three places where the three blade roots are ... ?

Again, it had to have come from Kipawa like this, because it vibrated right from the get go, and I never put any weight on it or hit anything with it ...

If I *can* get the blades even, it's a bummer that I can't try it out on the 45!

[GreenLake]

I was afraid that the blades would "relax" after bending, whatever the plastic is, it is not metal, but if that happened the result is still that the vibrations are gone.

The one thing that may have changed is how tight I cranked down the nut on the propeller. I think it's tighter now than when I took it off.

If I find a spare moment, I might take it off again and double check the shape.

[TIM WEBB]

Yeah, when mine was vibrating on the old motor, I played around with the tightness of the bolt, but it didn't seem to make any difference. Part of the reason I chalked it up to something wrong in the motor itself ...

[GreenLake]

So, checked it out, and the blades are fairly nearly aligned, that is, I'd be hard pressed to measure the difference and they look more like when they went on than when they came off previously.

If you really can't get yours to keep its shape, then I don't know. Have you tried bending more than needed, with the idea that partial relaxation would then hit the sweet spot?

If that doesn't work, I'd think "mild heat" but that can go horribly wrong (esp. since I don't know what kind of plastics are involved). Another idea might be some kind of jig where you can try to pull the blade into the right position over time.

[TIM WEBB]

I bent the one blade pretty hard - to the point where I was afraid I might break sumthin' ... ?

Didn't use any heat, but again, for me this is an empirical test, as I can't use that prop on the new motor anyways ...

I believe the Kipawa props are ABS, and I have no idea how that plastic behaves under "duress" ... ?

[GreenLake]

Tim, if these are ABS, then heat would allow it to be formed. However, knowing how much heat... Somewhat below 250 is enough to get a sheet to lose all form so you can vac pull it... lacking a mould, perhaps not what you want to do.