M25XP w/ HBW50 Transmission - Singing Prop

[Ward H]

My second season with our C30. New this season is a noise while motoring.
This is a 93 C30 with M25XP & HBW50 Transmission. PPS dripless water seal and 3 blade prop.

Motor sounds great at all RPMs while in neutral. It idles at 800 rpm.

When motoring in forward gear there is a whine like noise at 1,000 rpm. Going back to idle or advancing to 1,200 or higher rpm the noise goes away. The transmission does not appear to be slipping.

At first I thought it was the alt belt slipping but belt is tight and there is no sign of belt dusting.

The sounds appears to come from the prop shaft. The cutlass bearing had no play in it while it was on the hard this spring.

Other than the usual winter prep the only thing I did to the drive train was to add new zincs and cleaned up the bronze prop and shaft with a brass wire wheel.

Looking for direction to investigate the noise.

Thanks

 

[Capt jgw]

Do you know how old the Cutlass bearing is? Maybe the rubber has gotten hard causing the noise. That would actually reduce the apparent free play. One of my commercial boats had a pretty loud howl at certain rpms from one shaft. Bearings looked fine with no play at the last haul out (every five years for USCG inspection). At the next haul we replaced both bearings and the noise went away.
You could uncouple the shaft from the transmission and see if the noise is present then. If not it must be the Cutlass bearing or something else with the shaft or prop. While you have the shaft uncoupled you can turn it by hand to see if anything feels odd.

 

[jssailem]

Now that you are sailing more has the noise lessened?

 

[Maine Sail]

Sounds like prop tip singing... If the edges are not squared off a prop can sing a bit.... Could also be the PSS just needs to be burped.

 

[Ward H]

Do you know how old the Cutlass bearing is?

No clue. Surveyor said it looked good.

Now that you are sailing more has the noise lessened?

Not at all. The rpm range for the noise is very narrow, 1,000 to 1,200 rpm.

Also noticed the noise with engine off and in neutral, just before I put it in reverse for sailing.

Sounds like prop tip singing... If the edges are not squared off a prop can sing a bit.... Could also be the PSS just needs to be burped.

I did clean up the prop and shaft this spring with a brass wheel. Very well could have rounded off the edges a bit. That would be good news.

I burped the PSS but will try that again.

Here is a before and after of the prop and shaft. I started off just cleaning it up to check the size and didn't stop.


Many thanks.

 

[Richard19068]

I don't have a solution but I have what probably is the same noise in a narrow band at low RPM while in gear. Universal M-18 with the same transmission, standard packing gland and two blade prop. It has been going on for a few years. I thought it might be the cutlass bearing but at the last haul out it seemed fine so I didn't replace it. Maybe it is the problem as jgw suggested. Or possibly the prop tip, but I don't know if I want to file / sand much off the prop.
My workaround has been to just not run it at the RPM that generates the noise.
Please post if you find the cause.

 

[Ward H]

As I went out for a sail today I noticed the “whine” noise was lower in volume. Total engine hours so far this season is about 3 so I thought maybe it was going to resolve itself. Wishful thinking?

Once Sail’s were up I stopped the engine and as normal practice put the gear shift in reverse, which locks the shaft.

I was sailing on a close reach doing around 5.5kts when I thought I heard the “singing” again. Went below and pulled the cover exposing the shaft, PPS seal and flange. The shaft was not turning. Got a long screwdriver and used it to isolate the sound.

Sure enough the shaft, which wasn’t turning, was singing or at least transmitting the singing of the prop tips Maine Sail suggested could be the cause.

So I think @Maine Sail nailed it. The prop tips are singing at certain speeds through the water.

I can live with that.

 

[Richard19068]

Nice

 

[jssailem]

Good thinking, finding an answer.

 

[Maine Sail]

Once Sail’s were up I stopped the engine and as normal practice put the gear shift in reverse, which locks the shaft.

You'll sail faster if you let the prop spin....

 

[jssailem]

You'll sail faster if you let the prop spin....

True, but what happens to his transmission?

 

[dLj]

True, but what happens to his transmission?

I know I've heard of tranny's that need to be left in gear, but honestly, I've never been on a boat where this was the case.

The owner of this boat should know if his tranny needs to be left in gear.

I'm with Mainesail, unless this specific tranny needs to be in gear, put it in neutral and let the prop spin...

dj

p.s. I just looked up the manual for the stated transmission and it said to sail with the tranny in neutral. Now the owner should make sure the transmission in question is as stated...

 

[Ward H]

p.s. I just looked up the manual for the stated transmission and it said to sail with the tranny in neutral. Now the owner should make sure the transmission in question is as stated...

My copy of the manual for the Hurth HBW 50 says to use neutral, which allows the prop to rotate OR reverse to lock propellor shaft.

From the C34.org website:

The volume of the singing prop increases to an annoying level with the engine off, tranny in neutral and shaft turning.

 

[dLj]

Gotcha. Well, you certainly know your boat best. Good luck. Certainly looks like Mainesail nailed the source of the noise. I wonder if you could put some kind of dampening material on your shaft for now and when you pull the boat out of the water again figure out how to fix it.

For sure keep us updated on how you take care of this. Happy sailing!

dj

 

[jssailem]

For sure keep us updated on how you take care of this. Happy sailing!

And Happy Singing.
And Happy Trails to you til we meet again.

 

[Ward H]

I wonder if you could put some kind of dampening material on your shaft for now and when you pull the boat out of the water again figure out how to fix it.

Good idea, wondering how I could go about it.
It also makes me wonder if I could have picked up something on the shaft or prop that has altered something. I may dive on it just to take a look.

I did have the yard mechanic check it but I wasn't there when he did. With the boat tied in the slip he couldn't reproduce the sound.

Thanks

 

[dLj]

Good idea, wondering how I could go about it.
It also makes me wonder if I could have picked up something on the shaft or prop that has altered something. I may dive on it just to take a look.

I did have the yard mechanic check it but I wasn't there when he did. With the boat tied in the slip he couldn't reproduce the sound.

Thanks

Yeah, not real sure how to do that. First thought is to have a short length of some of that thick walled tubing, like sanitation hose, that has the same inner diameter as the diameter as your prop shaft. cut it so you can slip it over an open area of the shaft and then hold it on with like nylon zip ties. I would sure want to make sure it's not coming loose or moving if I were to try this... I'm sure you can come up with a better idea. Like maybe wrap that free section of shaft with gorilla tape... But from what I've seen you post on things, I'm sure you'll come up with a better method than what I'm throwing out here ....

dj

 

[jssailem]

Could you slightly alter one or more of the prop tips. That is if as MaineSail states the harmonic is in the prop tips.

 

[Ward H]

Could you slightly alter one or more of the prop tips.

Good idea.
If I dive on it I could take a file and run it across the edge of each tip. Worth a try.
We have a nice protected anchorage near the marina where we can edge in to 4-5' of water. At that depth it may not be too hard to do.

 

[jssailem]

You should be able to walk around on the bottom.. Watch out for snapping turtles.