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Hum and vibration


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Just got a 2005 Response LXi and during water test noticed a hum and vibration between 30 and 36 mph then it goes away. No hum or vibration under 30mph. 

Had a pre-purchase mechanical and electrical inspection done at the local Malibu dealer. I specifically asked to have them check for the hum/vibration.  They indicated shaft seal is good, shaft itself is good, prop is pristine (Acme 13X12.5) and they say tracking fins look properly aligned. Their explanation was hum and vibration caused by the tower (tube style). 

The boat had previous damage to the hull, prop/rudder/shaft and fins. All were replaced at the same dealer that did the inspection on an insurance claim to the time of about $14K (Canadian). 

What are the chances that the hum and vibration are coming from the tower as the tech indicated on the report; or the non spec prop being the issue (spec according to Malibu is 13X13); or maybe the tracking fins actually being slightly out of alignment (that can’t really be noticed on visual inspection)?

Boat looks great, runs great (other than the hum/vibration) and is pretty low in hours at about 450 hours. 

I appreciate any feedback from anyone who has experienced the same issue or had thoughts on the potential causes. 

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7 hours ago, Eagleboy99 said:

Grab the tower when it is vibrating and you will know.

I’ll definitely try that, but it sounds so strange that a tower could be the cause of the problem. Has intone else experienced that type of issue?

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On 7/18/2019 at 5:00 PM, formulaben said:

I'd check for any looseness of the tracking fins, strut, rudder, and shaft (cutlass bearing.)  They all should be rock solid.

I had a pre-purchase inspection done and tracking fins were aligned, shaft seal and shaft were all in good order (no unexpected play) and rudder was all good.

No vibration in the tower that I could feel @Eagleboy99 so now starting to second guess my self and wonder if I felt a vibration or if it was just coincidental with chop in the water.  Taking off the tower to see if that eliminate the noise/hum and then will feel closely to see if there is actually any vibration in the floor.  If there is I anticipate it could be an alignment/strut/bearing issue and will have to get that taken care of right away.

I"ll let you know what comes of tonight's testing.  I'd attach a video clip (not great quality) where you could hear the hum and the speeds (from about 28 mph to 36 mph), but not sure how to attach a video clip in the forum.

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  • 2 weeks later...

I had an alignment done and while the vibration has cleared up, I"m still hearing a whistle/sing between 28mph and 38 mph.  I haven't been able to talk to the tech that worked on the boat to find out if we're talking about the same thing, as he said the sound is normal, and that doesn't seem right to me.

If you click on the youtube link in my previous post you should be able to hear the higher pitched whistle/sing I'm referring to.  Any insight would be appreciated.  The only thing I can think of at this point is prop sing since I've had an alignment done and the tracking fins appear to be properly aligned as well.

I appreciate any thoughts any of you may have.

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7 hours ago, pnyk67 said:

I had an alignment done and while the vibration has cleared up, I"m still hearing a whistle/sing between 28mph and 38 mph.  I haven't been able to talk to the tech that worked on the boat to find out if we're talking about the same thing, as he said the sound is normal, and that doesn't seem right to me.

If you click on the youtube link in my previous post you should be able to hear the higher pitched whistle/sing I'm referring to.  Any insight would be appreciated.  The only thing I can think of at this point is prop sing since I've had an alignment done and the tracking fins appear to be properly aligned as well.

I appreciate any thoughts any of you may have.

That sound would drive me crazy

The earlier video is unavailable 

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Is there any way you could borrow a different prop to see if the sound changes or goes away? They say it's the tower; I don't accept that. I would take it off to prove otherwise 

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I’m betting on prop.  Put a new prop on it and I bet it goes away.  I had that hum at idle speed and high end and ended up being tiny little dings along the edge of the prop and a blade slightly out of alignment with the other three. .  I switched prop and then sent the noisy one off for redo.  Prop shop said one blade was out of alignment with the the other three and that is what set up the harmonic distortion/whirring/hum like what you have recorded.  All the best! Safe and happy boating! 

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17 hours ago, toddthelineman said:

Is there any way you could borrow a different prop to see if the sound changes or goes away? They say it's the tower; I don't accept that. I would take it off to prove otherwise 

I did remove the tower, sound persisted afterwards.  

Took to a different Malibu Dealer who found the shaft out of alignment and the cutlas bearing worn.  Had those changed, but the sign/whistle was still there in the same speed/rpm range.  I too am pretty convinced it's the prop and read that 4-blade are more prone to this than 3-blade.  The original owners manual calls for a 3-blade and when you look at props through Acme, using the manufacturer/model selector it recommends 3-blade props.  I don't know that prop sing is the reason they recommend a 3-blade, but going to give it a shot and see.  Unfortunately I don't know anyone who has a 3-blade in the right size (nearby) that I can borrow, so will have to buy one and try it.  At least then I'll have a spare prop if I ever need one.

 

Thanks for the feedback @BlackBluMalibu and @toddthelineman

The sound is really annoying, but at least you know it's me coming down the lake...

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Sounded like you were up to "noise" speed and quickly throttled back yet it persisted until the hull slowed down, not the prop (which was immediate.)  My guess is a tracking fin or strut is either loose or cavitating.

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No, we were accelerating from 28 mph to 38 mph and the sound persisted through that range. When we slowed down, the sound persisted until we fell under the 28mph. Strut was just replaced and shaft aligned.  Fins are straight and in line.

Acme indicated dull edges on the prop likely the issue. Just got a new ACME 525 prop so plan to change it shortly to see if that corrects the issue.

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On 8/13/2019 at 5:35 PM, formulaben said:

Sounded like you were up to "noise" speed and quickly throttled back yet it persisted until the hull slowed down, not the prop (which was immediate.)  My guess is a tracking fin or strut is either loose or cavitating.

So I’ve changed out the prop and the sound is still there. Since I know it’s not the prop, or strut/alignment issue that leaves the tracking fin. @formulaben you suggested possibly the tracking fin, any suggested fixes if the fins are all aligned?  I read something in another forum about the trailing edge of the fin needing to be lightly sanded or polished?

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I'm not an expert on the tracking fins but I thought they were supposed to be offset slightly? As for the cavitation issue, make sure they are all tight and check for nicks/dents all around. File and sand them smooth and see if that changes it.

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I think I would try to eliminate a few variables. 

Pour a little dish soap on your prop shaft just above the cutlass bearing and wet it with a garden hose so it is lubricated.  Make sure your kids aren't playing with the prop, then run the engine on a hose, at singing speed, in gear.  If it sings, it's not the boat.  If it doesn't, it is probably the boat. 

 

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