Scary, loud, intermittent transmission/bearing noise

[CdS2 Roland]

Growth on propeller and hull.... Its ideal for propeller cavitation.

[cwyckham]

Originally Posted by CdS2 Roland

Growth on propeller and hull.... Its ideal for propeller cavitation.

True. In this case, though, it has occurred with both a clean hull/prop and a dirty one. I do believe the vibrations from a fouled prop have made it worse recently.

[Lepke]

DeepFrz is right. Check your alignment. Also make sure everything is properly bolted down and not moving. Too many mechanics think they can unbolt the engine, trans, v-drive, etc., repair it, and bolt it back in without doing a proper shaft alignment. I'm 67 and been around ships and boats my whole life. In that time I've only had one shipyard do a proper alignment I didn't have to redo myself. Your alignment needs to be checked at every flange set. The flanges need to be within .002". Otherwise you get premature bearing wear. Most likely you have some damage (excessive wear) now.

[cwyckham]

Update: I've finally been down and checked the alignment.

First step was to spin the shaft. There was some crunching that sounded like mussel shells, then it spun freely.

Then I unbolted the coupling and tried to decide where the center point should be. Nigel Calder says you can approximate it by flexing the shaft around and finding the limits and then choosing the center of that.

With a Hurth v-drive, I can only flex the shaft so far before it hits the inside of the transmission output ring flange. It hits the flange before the shaft log in all directions and "feels" centered, but it's hard to say for sure (note, I have a PSS, so it's flexing all the way from the cutlass bearing).

I had trouble judging the alignment. It seemed to be a bit off, but when I spun the flanges it would be good. I was worried that I had a misaligned coupling or output flange, but then noticed there was a lot of gunk on the output flange. Once I cleaned it up, the alignment was excellent. I'm not sure if this would have been a problem once bolted on hard, but I'm glad I cleaned it up.

This is getting long-winded, but I'm not sure I'm closer to a solution. I feel like I have two possibilities:
1- There's some sort of problem with the cutlass bearing. This might be due to the inboard shaft end being in a slightly different place with the new installation. The cutlass bearing is only 3 years old, but maybe it was worn one way and now is getting pushed in a different direction?

Honestly, I don't understand how this issue would mean that I'd get this very sudden onset of the very loud sound that would then go away for a while once I decreased rpm for a few seconds.

2 - This is a new theory... The boat is horribly covered in sea life (coming out tomorrow for cleaning). I've read that a poorly cooled PSS can howl or squeal when it overheats. This is an issue on fast boats where a vacuum can be created and the cooling water sucked away.

The problem started after a new engine (maybe 20-30 hours after install), but this might be a coincidence. The boat is slowly choking with life and I could hear it around the shaft in the log. When I "burped" the seal, the water that came in stank like the water in the head flush hose after it's been sitting for a couple weeks.

What if there's so much life in there that cooling water isn't circulating and the shaft starts to overheat?

Last time we came in to dock, the howling was happening every minute or two. It's never been that bad before, but it always gets worse as a trip progresses. When I ran the engine in gear at cruising rpm for 15 minutes last night, I couldn't get it to go. Perhaps because the PSS seal hadn't heated up enough yet?

Is this plausible?

All that's left for me to do at this point is to inspect the cutlass bearing and prop over the weekend while I'm out of the water and hope for the best if they seem fine. I can't think of any other possibilities.

[cwyckham]

Hauled it last weekend. Incredible amount of growth on the boat and running gear.

The cutlass bearing looks fine. There is no play side to side and about 1/32" up and down. Nigel Calder says I'm fine up to 1/16".

Had no issues on the way to the haul-out (quarter mile from the slip). We were going really slow, though!

Had "the noise" again on the way back. But... I had forgotten to burp the PSS. So my theory may still hold out. Need to play some more.

[shakey doug]

1/32''[30+thou] is a lot of clearance for shaft dia you are running.
Try "Singing Propeller" at Dr Googles Clinic.

[cwyckham]

Originally Posted by shakey doug

1/32''[30+thou] is a lot of clearance for shaft dia you are running.
Try "Singing Propeller" at Dr Googles Clinic.

Cool. I'd never heard of prop singing. Thanks for the pointer.

However, since it's a harmonic vortex shedding effect, it would be very limited in rpm range and would always be there. It wouldn't "turn on" suddenly.

[Sailmonkey]

Our prop sings when the boat is being pushed by wind or waves.....ie the prop is turning but not really thrusting. All other times it's quiet.


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[shakey doug]

This situation will and does turn on and off randomly.

[cwyckham]

Originally Posted by shakey doug

This situation will and does turn on and off randomly.

Interesting. I'll file it away as a possible cause.

I burped the PSS today and had a nose free trip. We'll see if this keeps up

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[transmitterdan]

I think you are on to something with the dripless shaft seal. When they are dry on the ocean side they can make some really frightening sounds. A lot of sound but no real harm is done if stopped in time.

Sometimes a lot of marine life will create gas bubbles in the shaft log tube. Also, some sea bottoms have a lot of naturally occurring gas bubbles. If your shaft is like most the uphill end of the tube is where the shaft seal sits. So bubbles tend to accumulate at the seal. Burping every day or two will remove the bubbles. I think this is one reason that new seals now come standard with a hole for installing a piece of tubing to form a stand pipe so the bubbles can escape.