Harmonic resonance from outboard

lloyds · Posted: Mon Jul 23, 2007 5:14 pm Post subject: Harmonic resonance from outboard

Anyone ever hear the "wet finger on the crystal goblet" sound emanating from their outboard? Mine started doing it about 30 hours of use earlier. It is between 1800 and 2400 rpm. I finally got worried enough about it to take it to the shop. They pulled the magnetic plugs to be certain I didn't have a bearing going out. No filings were found. They could not duplicate the sound with the engine in the tank. This is on a Honda 50.

Sea Wolf · Posted: Mon Jul 23, 2007 7:45 pm Post subject:

lloyds-

Do you have someone else who can drive the boat while you investigate the sound's origin?

Can you tell what part of the motor it's originating from?

Does it resonate with the cover (shroud) off?

If it's harmonic resonance, you should be able to change something and defeat it, at least according to theory!

Do you have a different prop you can switch out with it?

Do you have a hydrofoil you can remove or adjust differently to change something about the resonance characteristics?

Have you checked your transom bolts and motor control connections for looseness or vibration when it's happening?

Could it be coming from a tuned intake or exhaust system?

How about some good, cheap ear plugs? (Just kidding!)

Hope you find it's origin!

Joe.

TyBoo · Posted: Mon Jul 23, 2007 8:15 pm Post subject:

If this strange noise happens only when in gear around that RPM range then my guess is you have a Solas or Honda-branded (made by Solas) aluminum prop on it. Nine out of 10 will do that. Sportcraft Marine, the Oregon City CD dealer, at one time wouldn't even sell Solas props because of the squeal they would make. All three Honda brand props I have used would make the racket in that RPM range, which just happens to be at no-wake speed while running the channel to my marina. Annoying, but harmless.

Fairbro · Posted: Mon Jul 23, 2007 9:12 pm Post subject:

I've had the same shrill note from ONLY ONE of my two Honda 40's. I noticed it on the first cruise and the fact that it is 5 years later and I am still hearing it testifies to it's elusiveness. It is especially aggravating in no wake areas which I am often in. If you find the answer be sure to post it!

lloyds · Posted: Tue Jul 24, 2007 11:46 am Post subject:

Thanks everyone for the replies. I had a feeling the prop was the problem but when I couple the beginning of the sound with the fact that the gps has been giving me a low voltage alarm when I restart the engine, and that has been happening about the same amount of time I got a little worried. I took the boat to the shop and they put the engine in the tank and couldn't reproduce the sound. I would guess because of all the turbulence in the tank. They did check out the alternator and it was okay. They pulled the magnets in the sump and there were no filings or particles so they are reasonably certain no bearing is going out. I have three props, all Honda. One is too much diameter, one is the correct prop but was damaged in Alberni Inlet and poorly repaired, and the third is a brand new prop with correct pitch and diameter. Thinking back using the damaged prop I don't notice the sound. So that is probably the solution. Thanks again.

dogon dory · Posted: Tue Jul 24, 2007 2:26 pm Post subject:

Sorry, Folks - Post Deleted By Author

TyBoo · Posted: Tue Jul 24, 2007 3:01 pm Post subject:

Moxieabs · Posted: Wed Jul 25, 2007 9:11 pm Post subject:

With my Honda 90 it is definitely the Solas aluminum prop; no squeal with a four blade composite prop. Problem is the ComProp is a lot slower on top end so I put up with the noise at no wake speeds and carry the platic prop for a spare.

Mr. Fisherman · Posted: Fri Jul 27, 2007 6:47 pm Post subject:

I had a similar issue with my Suzuki. It was a loose bolt on the steering arm. Check all the bolts on the transome for looseness.
Hope you find the culprit. It sure made a difference when I did. Also check your cowling. Occasionally you may need to tighten it as well.

jlastofka · Posted: Mon Jul 30, 2007 1:45 am Post subject: High pitched engine sounds....

I have a high pitched sound at a certain narrow RPM range on my 9.9 Honda kicker. It seems to drop off some if I tilt the engine up away from the nearby trim tab, although holding the trim tab by hand doesn't damp the sound.....

Perhaps it could be something about the prop, as others have suggested.

I have just barely heard the sound a few times from the Honda 90 main engine, but extremely faint and rare.

It doesn't sound like a prop noise to me, but I have no real idea where it's coming from, so... maybe. I may get another kind of prop as a spare and see what happens.

Jeff Lastofka

jlastofka · Posted: Sun Sep 16, 2007 1:53 pm Post subject: High pitched prop noise?

I've had a ringing sound (or squeal as some others have said) at one particular narrow RPM range on my kicker.

Yesterday, in the driveway, while working around the back of the boat, I noticed the kicker prop will ring like a bell if I whack it with a fingernail. The ringing sounds like the same frequency as the squeal when it's running; at least from memory it seems that way. The main prop just makes a dull thud. I also noticed the kicker prop was rattly loose on the shaft (just a tiny amount), so I tightened it a little. It still rings with the fingernail trick, but it's mounted differently, so maybe things will change.

I've also noticed at times a very faint version of the same sound when running the main engine. I'm now guessing that the kicker blade ringing can be slightly set off by what little vibration comes through the transom from the main when I get to just the right RPM for it.

The main prop is rubber mounted I believe (VTEC 90) and the kicker prop is just metal to metal on a spline (9.9 Hi Thrust). They're both the stock Honda props that came with the engines.

I could try a rubber bushing of some sort, but I have a feeling the blades will still ring. I need to start searching for a different prop to try as a test. Plastic, wood, rubber, whatever Smile

Jeff

lloyds · Posted: Mon Sep 17, 2007 7:19 pm Post subject:

Be interesting to see what you find. I am still having the ringing, but try to ignore it.