High-Pitched Whine

[edwardc]

It seems that every time I clear up one problem, another one emerges.

This afternoon, after getting my shaft packing redone right, I took the boat out for some engine sea trials. Finally! This is the first time the boat's been under its own A4 power since last July!

The new Moyer-rebuilt engine ran great. Was able to run it (breifly) up to just over 3000 rpm at wide-open-throttle (1500 shaft rpm due to 2:1 v-drive). Never could get above 2400 before.

But somewhere around 1200-1500 rpm, a loud high-pitched "whir" or "whine" develops. Wooooooooo... Sounds like a cheap halloween-ghost sound effect. It dissapears at 2000 rpm and beyond. I ran below and stuck my head in the engine compartment, but couldn't localize it. It actually seemed louder in the cockpit than in the engine compartment.

My only idea for the cause is that the boat has "flexed" or relaxed some since it was launched 2 weeks ago, and the engine alignment I did is no longer correct, and the sound is coming from the cutlass bearing in the strut.

Does this noise sound like the sort of thing that be produced by a bad alignment? Or is it something else?

[Al Schober]

Certainly could be a stick-slip noise from the strut bearing. It's kinda like the noise you get when you rub a wet finger on the rim of a wine glass.
I wouldn't blame your shaft alignment job. It's probably more that the strut is out of line with the shaft. You may have changed the way the shaft goes through the strut when you did the alignment, but it's what it is without a major redo.
Personally, I'd live with it a while and see what happens. The new contact points inside the bearing will wear in eventually. It's not like you were a sub driver, worried about someone picking you up on sonar..

Al

[hanleyclifford]

I don't know too many who can get 3000 rpm - can I ask what size and pitch prop you are using?

[edwardc]

The prop is a 3-bladed, bronze, Michigan, 15RH8.

Remember, I've got a 2:1 V-drive, so 3000 engine RPM is only 1500 shaft RPM.

[hanleyclifford]

Understood, but even with 2:1 your rpms are impressive. Your pitch is low for a 2:1 and that probably explains it. You could probably get away with more prop, say, 9 or 10 pitch.

[67c&ccorv]

Propeller cavitation maybe?

Anything like the sound of this pump cavitating at :34 seconds?

http://youtu.be/guHGpOzDa9A

[edwardc]

Propeller cavitation maybe?

Anything like the sound of this pump cavitating at :34 seconds?

http://youtu.be/guHGpOzDa9A

Nope. Doesn't sound like that at all. More of a high-pitched moaning or wail. Somewhat like the sound of high winds in the standing rigging.

I did some more tests today. Here's what I found:

* Sound starts around 1100 rpm, peaks at 1400, disappears at 1800.

* Sound occurs when in-gear and under way.

* Sound does NOT occur when moving in reverse at any rpm.

* Sound does NOT occur when in-gear tied off at the dock at any rpm.

* Sound does NOT occur in neutral at any rpm.

* Using a broomhandle "stethoscope", I listened to the alternator, the new raw-water pump, the fresh water pump, and the v-drive. None of these seemed to be the source of the noise.

The fact that it only occurs over a limited range of rpm suggests that its a "resonance" phenomenon, rather than a slipping belt.

The fact that it only occurs in-gear seems to suggest components from the transmission through the propeller.

I don't know WHAT to make of the fact that it doesn't occur while in-gear but tied off to the dock..

[hanleyclifford]

When the boat is tied to a dock and run in gear the most force is being applied to bearings in the gear box. Possibly the increased pressure blocks the bearing noise in the box that might otherwise be heard if the boat were moving freely.

[edwardc]

After trolling through lots of related, and unrelated, posts here, I came up with the following two items that seem to possibly be relevant:

I had the same funny noise on my boat. Kind of a whining noise. It went away when I shifted into netural. While in gear it would be there up to ~1200 RPM then sort of go away when I increased throttle. At some throttle settings it would fade in and out. I thought the belt to the alternator might be slipping. After I removed the belt to the alternator the noise was still there.

Anyway it turned out to be the packing gland. On my boat the end of the engine and the packing gland are close together. It was hard to tell where the noise was comming from. Adjusted the packing gland and the noise went away.

My engine would "sing" at 900-1,000 RPM...it ended up being the shaft rubbing a hole in the shaft tube.

Both of these describe a "singing" or "whirring" that only occurs at mid rpms, in gear.

If its the packing gland, that's harmless and easy to fix.

If its the shaft rubbing the tube, I don't want go through what Shawn had to last season!

Unfortunately, rubbing the tube is starting to sound likely. It explains why it only happens in fwd gear, not reverse. In fwd, the shaft is under compression. This would exagerate any slight bowing. This would then resonate at a particular rpm making it worse.

In reverse, the shaft is under tension, which wouldn't make it bow.

Still doesn't explain why it doesnt do it at the dock, though.

[sastanley]

ed,
It took 30 years to rub a hole in it, though.

As for the no sound at the dock, I agree with Hanley, & here is my $0.02. It is all harmonics and a certain chain of events..simply, at the dock, you aren't moving, so the loads and motion on the shaft are different, and it won't sing..(it may still be rubbing though!)

Once you get all this worked out, you need to make a movie of the engine at 3,000 RPM..I bet it sounds impressive!!

Mine was really out of whack...you could see the prop shaft wobble. I'd try a re-alignment..I know they are a pain, but yes, the boat may have settled. It must really be a pain with the V-drive in the way!

[Dave Neptune]

Singing

Edward, many times I have come across this on engine redo's. Did you have any work done on the prop? If so it could be the prop "singing" from resonation of blade vibration at a specific rpm range, it will come and go at more than one speed (RPM) sometimes too. A prop shop can put a small relief grind on the face side of the leading edge of the prop. Most reputable prop shops do this on sailor type props. When they sing like this the noise seems to come from almost everywhere as it transfers through the drive line into the hull. You may even be able to hear it by sticking your head over the side and listening.

A likely suspect if the prop was changed at all.

Dave Neptune

[edwardc]

No, the prop's the same. All I did was clean it and recoat it with Pettit Zinc spray coating.

[Dave Neptune]

Cleaning?

Edward, did you happen to "clean" and file the leading edges of the prop? If the prop is unchanged it's probably not it.
Have you tried a stethescope on the prop shaft. To have a "hi-pitched" whine at low RPM's would probably be a bearing and the only one spinning very fast is the alternator.
Since you said you could hear it outside almost better it still makes me think of a prop "singing" still.

Dave Neptune

[edwardc]

The cleaning was with a drill-driven wire brush, a hand wire brush, and some 120 grit sandpaper on the "flat" surfaces only.

The old zinc paint (it appeared to have been brush-applied) was incredibly tenacious. Rather than risk removing any bronze, I left the most stubborn of the old paint on. I figured if it was bonded THAT well, it wouldn't be a problem, as long as I got it smooth.

See for yourself:

[JOHN COOKSON]

This May Be A Red Herring

Is whatever that was giving you a tight fit around your shaft during the recent repacking job have anything to do with this noise?

TRUE GRIT