Would just a bent prop cause vibration?

I hit an underwater log today on the Willamette. I wasn't going very fast... probably only 5mph or less when I heard that terrible "thud" underneath. Honestly, I might have even been in Neutral... can't remember.

After that my boat vibrates when you give it throttle... the more throttle the more vibration. So I limped back to the ramp and pulled her out of the water... looks like just a bent prop (only one of the blades... see top blade in pics below)

But would a bent prop cause that vibration? The shaft and everything else appears okay.

I'm trying to decide if I should take the entire boat to the dealer or pull the prop off and take it in for repair at an independent prop shop. I'd hate to get just the prop fixed only to find the vibration is still there.

Thoughts? What would you do? I'd like to keep this repair to a minimum $$ as it's my 2nd underwater hit of the season. The first one was ugly.

Is there a way I can diagnose this myself? Run some sort of out-of-water test to see what's causing the vibes?

What would you do?

Good bend!
Yes, a bend much less than that will cause a lot of vibration. Pull the prop and get it repaired. I doubt there is any other damage.
I keep a second prop in a kit with replacement tools.

Art is right, a bend that you can hardly see with your eye will cause a bad vibration.

You can remove the prop yourself with a prop puller. You can rent them from a marina, or purchase one for about 50.00 - 70.00.

When using the puller, you will tighten it down until the prop "pops" loose. Putting the repaired or new prop on is easy, Just tighten the nut and use a new cotter pin.

been there, done that - well my buddy was driving to pick me up in the water after i fell. he felt a little thud. prop had a little bend. caused huge vibration. fixed the prop and all was well again.

btw - they guy at my marina just banged it out in 3 minutes ... but he has years of experience...

I once hit a log, simular situation, ... boat was vibrating like mad. I pulled the boat, looked at the prop, it looked fine... so i got all worried, sent it to a shop for THREE weeks JUST to get an estimate on a new shaft, etc... (Expecting several grand worth of repairs)

I eventually got frustrated and pulled the boat from the place. My friend told me to go ahead and replace the prop cause sometimes even "unseen" damage on the prop can cause vibration.

$400 dollars later, my boat was running like new. After I pulled the prop I could see a slight bend in it (so very little) -- its amazing how if you get the things off kilter just a bit, they totally vibrate the boat to death.

I sent the prop in and now have a spare in case the situation happens again.

If your worried about additional damage, you can pull the prop, start the boat up and watch the shaft turn.

You'll want to get behind the boat while you have a buddy just putting it into gear. watch the shaft for wobbling. There should be a little line, like a spiral on the end of the shaft where the cotter pin goes through. If it turns a smooth rotation, your good. If it kind of wobbles you need to have it looked at.

Do not put it in gear out of the water; you'll cook the cutlass bearing. 98% chance your only damage is the prop.

Correct prop installation instructions, just for reference.

I just tore up my prop a few weeks ago. I took it to the prop shop and had it repaired. I put the repaired prop back on and the next time out I noticed a slight vibration just as you described with yours. So I took the prop back to the prop shop and sure enough, although the blades looked fine the prop was out of balance. The prop shop rebalanced it and now the vibration is gone.

So to answer your question, yes the slightest ding can cause a vibration, even if there is no visible damage.

(Message edited by Nauty on May 17, 2009)

your best bet would be to send it back to ACME or OJ (whichever it is) and you will know they will get it as close to normal as possible. You do know that it will never be as perfect as when it was made, but the difference would more than likely be negligible. CNC props are cut out of a block of metal to very tight tolerances. It can not be repaired to this tolerance.

One option would be to buy a new one and use the repaired on as a spare.

edit
by the way, I have seen a very small knick (1/8 of an inch in the tip of a blade) make a prop vibrate so bad it was unusable. If you were going slow, you probably didn't do any damage to the shaft and the prop should fix your vibration.

(Message edited by 1boarder_kevin on May 17, 2009)

Trace, if he's using a fake a lake and just dropping it into gear... no additional throttle, he'll be fine! Do I recommend slamming the throttle w/ a fake a lake.... no way, but just dropping it into gear, is fairly safe for a short time.

I've done this many times on boats and never had issues. Dealers have even told me to do this.

CNC props still have to be balanced by hand before they leave the factory. They can be repaired good as new by a good prop shop.

Tanner - a fake-a-lake doesn't do anything for the cutlass bearing, but don't let me stand in your way. I would at least soak it with lube.