Noise after changing Prop

[stingray609]

Hey all,
First time posting here so take it easy on me! Yesterday I found a "new rock" in the lake...chewed up the aluminum 3 blade prop a bit and called it a day. I went to get a new one and decided to try a 4 blade setup this time to help on the initial hold shot when wakeboarding. My 3 blade was a 14.25X21 but the 4 blade the shop had was 14x20. I know its been reccomended to drop a inch of pitch when going to a 4 blade and the shop said the 1/4" diameter wouldn't be very noticible.
So, later in the evening I put the boat back on the lake and noticed a quicker start and improved cornering as expected...the issue is a whistling or whining noise when you get over 2900 RPMs now. I don't remember hearing it even after the hit on the other prop yesterday. I lifted the engine cover but couldn't hear it in the compartment when I was going so it sounds like its coming form the stern. Anyone have any experience or suggestions?

1994 Stingray 609ZP- 180hp Mercruiser- Alpha one Gen 2 drive (rebuilt 3 years ago)- 1575lbs plus engine- quicksilver aluminum props before and after

 

[sho3boater]

Re: Noise after changing Prop

Like it is coming from the outdrive? Double check the prop to make sure it can't contact the case or rub it. Check your lube level, I guess I'd start there. Also check the power steering fluid and belt tension on it.

 

[stingray609]

Re: Noise after changing Prop

I can't nail it to the specific location but its not from the engine or belts. ...not a screaching noise....more of a whistle or whirring. Lube level was fine, I'm gonna duck out of the office for an hour and go fire it up in the driveway.

 

[sho3boater]

Re: Noise after changing Prop

I get a noise like that with the force outboard I am running right now. It does not change with rpm it just does it above a certain rpm and stops when you go back under it. It does not always do it right away. Best I can figure right now it is the LU gears slinging the lube off the gears. It almost sounds like a carb howling, like an old quadrajet on a 1980 GM car when you floor it. But again, if I hammer it WOT it does not do it right away so I know its not the carbs. It could be a bearing in the motor I suppose, when or if it breaks I would find out I guess. Kind of a foghorn sound and barely loud enough to hear over the normal motor/boat sounds at wot. I don't think it is the prop, it does not sound like a surfacing prop sound to me and IIRC it does not change if I move the trim.

 

[hwsiii]

Re: Noise after changing Prop

Stingray, what you probably have is what is alled a singing propeller, it an be ured by either hamfering the edge of the prop or adding a little up to the trailing edge. You an try another prop on the motor and if the sound goes away it is definitely a singing prop. Usually they only sing at a ertain RPM range beause the noise itself omes from harmonis set up by the prop.If it is still there start heking your lower unit as you have a problem that needs fixing before it beomes major.


H

 

[sho3boater]

Re: Noise after changing Prop

Possible it is the prop. I had mine worked to lower rpm a little and it was not as bad after, but I figured it was the lower rpm causing it. They thinned and polished it as well as adding a little cup. I told them 100-200 less rpm. It didn't go faster but rpm was in range instead of too high.