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Andrew63

Prop sing at ski speed

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Andrew63

Hi.

Boat came with a ACME 525 (13x11.5)

Had a slight vibration so had it checked & balanced.

Slight improvement, but still not ideal.

Purchased a new ACME 515 (13x12)

Speed was down with a max speed of 39.5 MPH at sea level with 2 adults full tank of gas & one footer hence the change to the 515.

2011 RLXI with 350 Monsoon.

Speed picked up to a max of 40>40.5 MPH.

WOT went from 4520 to 4570, stil below the max operating range 4600>5200.

Yes, doesnt make sense RPM would pick up with speed using a higher pitched prop.

Have noticed the old prop has more cup so this may have been altered from standard specs.

The new prop runs good with regard to balance & vibration with no noticable vibration.

But, at cruise & ski speeds say 30>36 mph, I have this high pitched almost tuning fork sound I beleive to be prop sing.

No prop sing at low speeds which is where this normally occours if an issus with a prop.

Any ideas where to start?

Most of the posts I have read regarding prop sing occour at low RPM

Edited by Andrew63

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toddthelineman

The responses I ski behind are much faster than that. More like 47. 45 with a footer or two and a boat full, no problem. I wouldn't think that has anything to do with the sound you are hearing.

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Indebound

Is the sound your packing nut packing? I have the Virtually Dripless type and it makes some noise sometimes.

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Andrew63

The responses I ski behind are much faster than that. More like 47. 45 with a footer or two and a boat full, no problem. I wouldn't think that has anything to do with the sound you are hearing.

Only mentioned the speed as the reasopn for changing from the 525 to the 515, bit of an experiment & the newer TXI or older LXI generally come standard with 515

Agreed, the speed is down which I have been chasing reasons for awhile now.

Tried removing the CATs, plugs.

Is the sound your packing nut packing? I have the Virtually Dripless type and it makes some noise sometimes.

Have the old fashioned Gland type nut with packing.

have lifted the floor & the sound ain't comming from the engine, transmission or shaft seal

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WINEGRAPEGROWER

The new LXIs are slower even with added HP...Malibu changed the hull, specially the bow somewhere in 2004 -2005 and later. I ski buddy has a LXI 2004 and the bow is more sloped, while my 2010 LXI is more angled....say 60 degrees off horizontal, while the 2004 is more 45 degree or less off horizontal.

The 2004 has the monsoon while the 2010 has the LS3.

I swapped props to get a better hole shot as the 13x13 would drag a skier a tad before planing....dropped to a 31x12 and began experimenting...ending up with a 13x12.67 with lots if cup.

even with the LS3, which is more TQ and approx 150 # less engine weight than the 2004 monsoon, I can't get close to 50 mph....only did WOT throttle a couple of time, so not sure exact RPMs and MPH

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ahopkinsVTX

FWIW, the hull changed in 07 with the second gen LXi and then again in 12 when the TXi was introduced. Not as much of a change to the TXi though.

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Bill_AirJunky

The singing can easily be the prop. My own prop did it at around 1500 or 2000 rpms. It was reworked after it was bent hitting the sandy lake bottom a couple years ago.

You can take a sanding block & run it lightly over the leading and trailing edges of each blade. Sometimes it takes a few passes with the sanding block for the singing to go away.

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Andrew63

You can take a sanding block & run it lightly over the leading and trailing edges of each blade. Sometimes it takes a few passes with the sanding block for the singing to go away.

This is where I am finding various fixes.

Found talk about dulling off the sharp square edge on the trailing suction edge

Then ACME talk about squaring off the trailing edge to ensure sharp edges in previous posts but this is to rectify sing at low RPM

This is the first time I have heard about dulling the leading edge & trailing edge.

I have a query in with ACME & will see what they offer as a soloution.

Thanks for the replies I think I will work on the most popular answer as a starting point

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Bill_AirJunky

Try running your fingers along both the leading and trailing edges instead. I'm not saying to sharpen or dull the edges, but to check for any oddities. Usually you will find the problem is a burr or odd transition on one blade.

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bandStrider

I had similar problem, reworked prop was singing at low cruising speed, like 25 mph. Sanded the edges and it went away. When you do sand, make sure you're not overdoing it, and one way to stay consistent is to put a full sheet of paper on a flat surface, like a tablesaw if you have one, and lightly move the prop across it. This will keep you from doing one blade more than the other. Of course if the burr is running down one of the faces of the blade you have to do it by hand. For mine, I just needed to slightly flatten the sharpened ends of the blades.

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Andrew63

Had some recent prop work done & requested they look for an answer to the singing as speed.

they were stumped & tried altering my 525 to have a variable pitch from 11 leading edge to 12 on the trailing edge.

made no difference still sings at ski speeds.

almost at the stage of buying another new 525 as this is getting frustrating to say the least.

the singing is so loud you can hear it over the engine noise

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Dare2goBare

Prop sing...you got to love it, ya right, mine sounded like a phone ringing.

Had the same issue when I bought a brand new replacement 515. Though it was at low RPM,

and as op have stated squaring off the trailing edge is the answer, now in your case your experiencing

it at a hight RPM, could it be a combination of slight out of balance prop, with a unsquare trailing edge?

I would start with the trailing edge and go from there. Good luck with it all.

 

Edited by Dare2goBare

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electricjohn

First thing that came to my mind was cutlass bearing.

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