Singing prop shaft!?

[Khayamanzi]

Well, just returned from the weekend out. Tried everything and....no difference!

 

One boatyard suggested that maybe the prop was a litle too high in the water and was causing cavitation. During the summer I did move some ballast from the stern a little further forward so have now moved it back. It seems a little better but is very intermittent - comes and goes as it pleases! I have also taken an MP3 recording of the sound if anyone thinks they might be able to help if they heard it.

 

Click here to open up your media player and hear it!

Edited March 20, 2005 by Khayamanzi

[Amicus]

Where was the microphone placed? i.e. where are we hearing it from?

[Khayamanzi]

It was recorded through my Ipaq handheld computer and I simply laid it on the back deck resting on the raised flange around the diesel filler next to the tiller bearing!

[Amicus]

I worked as a boat-builder (salty) for 25/26 years, and still dabble.

I think you would be wise to assume “worst case scenario” here. If it were my boat I would assume a problem with the shaft/stern tube, it is the right “pitch” for the shaft/prop ringing. If that assumption is correct, damage is being done by running the boat. On a salty boat I would put the boat on a drying berth for a tide and check the bearing for wear and lubrication. What the hell one does on a canal I dunno, can one dry out in a lock? Put the back end on the cill?

Don’t want to sound alarmist but I do think some care is in order here.

[Khayamanzi]

Cheers for this. As it happens I have an engineer who should be ringing me this week to book a slot where we can pull the boat out up a slipway they use for hull blacks and take a look. The yard is only about 30 mins from here and that would be the next trip out anyway so hopefully he can sort it out for me then. There doesn't seem to feel any play in the prop shaft at all - no give or rattle when I yank it about.

[Amicus]

. There doesn't seem to feel any play in the prop shaft at all - no give or rattle when I yank it about.

<{POST_SNAPBACK}>

Right, a loose bearing, I dont think, would make that noise, I would be concerned more with a lack of lubrication, but then if your winding the greaser????.........I dont understand what is going on but I do think it needs investigating asap.

Please let us know the result of your trip ashore.

[Khayamanzi]

I agree Amicus, the first thing I thouht about was the grease, I even unscrewed the entire greaser assembly and re-packed it and then pumped a load through to make sure there wasn't any air bubbles. Grease now oozes very freely from round the packing gland so that is a definate one out of the equation, checked the prop for any bits 'anging off, tightened the gland, loosened the gland, been into the weed hatch very thoroughly, (including checking right from the exit to the rudder,) moved ballast to the stern so that the prop is well into the water which it now is. Someone mentioned that the prop may be too big for the engine, (a 42 HP Isuzu,) so the engineer will check that out but if that was the case I am puzzled as to why it has only just started and didn't do it from new. (In fact I'm puzzled as to why it's doing it at all on a boat less than 2 yrs old!!)

 

I will certainly post any solutions that are identified here, so that others can benefit should this topic ever rear its head again!

Edited March 20, 2005 by Khayamanzi

[Amicus]

Did you notice grease oozing out of the rear of the tube, just in front of the prop boss? Thats where it needs to be.

Edited March 20, 2005 by Amicus

[Khayamanzi]

I didn't really notice this. I think it was coming out both sides but can't really be sure.

[John Orentas]

Andy.

 

What Amicus is saying is what I was getting at in my last thread, the grease is needed to the rear of the grease input not forward of it, you must feel around the prop shaft where it emerges from the rear of the stern tube.

[DHutch]

You must feel around the prop shaft where it emerges from the rear of the stern tube.

 

And for this you need to take the top of the weed hatch and get yer hand in there.

[Khayamanzi]

OK, supposing I feel around and can't feel any grease at the back - what might be causing that and how would I solve it?

 

I have to say, I'm not sure if I did feel any when checking the prop shaft in the weed hatch where it exits the stern tube.

[Amicus]

deleted, sorry, I didnt dead your post correctly

Edited March 20, 2005 by Amicus

[Amicus]

OK, supposing I feel around and can't feel any grease at the back - what might be causing that and how would I solve it?

<{POST_SNAPBACK}>

If grease is not getting thru the bearing i can’t imagine where it’s going. This has to be the subject of your investigation when ashore, Am certainly intrigued though.

[John Orentas]

Andy.

 

Tighten the stern gland a little more than normal to make sure no grease can get out at the front end. Force the greaser as much as you dare.

 

Note the grease comes out at the rear in the form of a very, very thin film but if you start off grease free fingers you should be able to detect it.

 

If for some reason it will not force through, substitute the grease tube fitting for a conventional grease nipple, force grease through with a lever action grease gun. Take fittings with you to go from 1/4" BSP female in the stern tube to whatever the grease nipple is.

[Khayamanzi]

Just to update this one - I definately have a 'singing prop' The engineer thinks I've caught it somehow in a way that has made it resonnate at this pitch as it turns through the water. I am now sitting here today as the prop is being replaced. I have tried filing it with a file but can't seem to solve it so decided to bite the bullet and get it changed - will let you all know if that certainly solves it when I cruise the boat back home tonight.

[David]

Amicus is more than likely right, singing props are well known to Carvers who often have to fix cheaper ones by re-machining and putting a sort of groove around the blade edges. Most props cheap'ish or otherwise are OK but sometimes either a chip or knock or even over tightening on the shaft can start the singing. If it turns out loosening fixes it and the gland packing is OK live with the drip (the gland should drip just a drop every so often or else it is to tight). If you still have the singing it sounds like a prop off job and clean up any damage or sending to Carvers or similar for checking and fixing.

Chap moored behind me had his done 3 weeks ago, persistant singing on new prop (fitted after Christmas) they found 3 different pitches on each blade and sorted that and put their groove around the edges £50.00. Before anyone asks why he didn't get it sorted by the place that sold the prop he did try but the replacement sang also. He didn't know til he got it sorted what was wrong and then he got his money back.

Why he had new prop etc is long and complicated and involves a 240V alternator etc etc etc.

David

[Big COL]

Just to update this one - I definately have a 'singing prop' The engineer thinks I've caught it somehow in a way that has made it resonnate at this pitch as it turns through the water. I am now sitting here today as the prop is being replaced. I have tried filing it with a file but can't seem to solve it so decided to bite the bullet and get it changed - will let you all know if that certainly solves it when I cruise the boat back home tonight.

<{POST_SNAPBACK}>

 

I had a singing prop on my first boat and an old wise man of the cut said I can fix that for you all you need to do is hit one of the blades with a hammer and take it out of balance. I could follow the logic of how it would stop it singing but could not for the life of me see why anyone would want it out of balance when you have carefully aligned the drive chain, I declined his kind offer.

When the boat came out of the water I was intending to have the blades machined. The guy who was to do the machining said if you are in any way practical you could do it your self on the boat. What I had to do was square face the edge of each blade, this I did and the singing stopped.

[Khayamanzi]

Thanks for the extra replies - I am now £400 worse off and the singing has also got worse off - where do I go now!? (apart from the samaritans or the local off licence!) A brand new prop hasn't solved a thing can anyone supply the phone number of any of these amazing wizards who can sort it out for me!

[Richard Bustens]

EAR PLUGS ????????

 

52p from Boots

[John Orentas]

Andy.

 

Just to re-cap the noise only occurs, in gear and the frequency changes with the speed of the prop shaft /prop ?

 

I suppose we are grasping at straws now other than the possibility that one of the early suggestions was correct and not fully followed up.

 

Gearbox output shaft bearing, badly worn stern tube bearing, engine mounts allowing metallic contact to the hull. Did you run it without the prop shaft coupled up, if not can you try that.

 

Did you pull the prop shaft out and have a look at it.

 

Going back, have you actually seen grease emerging from both ends of the s'tube bearing.

 

Silly question but does it 'sing' when moving through the water as well as moored.

 

What type of stern tube is it, welded in, bolted in, 'flexible' type.

[Khayamanzi]

John thanks for the detailed reply and ideas. yes I did check the grease situation the last time this thredad was alive and grease is definately coming out of the back end of the tube. The noise is actually most pronounced when the boat is moving through the water - in fact it is sometimes hard to replicate when moored. Just spoken to the yard and they are going to change the prop again on Monday for me but this time use a slightly smaller prop as I have a 42 HP engine and rarely use that amount of power so we will see if that stops it, again - watch this space!

 

I think the ear plugs idea might be the best thing yet, someone in my marina suggested a CD player and a recording of a very loud bollinder engine!!

[Richard Bustens]

No chance that there is a bit of plate dislodged that the water is hitting is there?

[Khayamanzi]

Where abouts might that plate be Richard?

[Richard Bustens]

Anyware on the back end or a rubbing strake bent a bit that the water could hit etc is there a bure on the rudder where something has hit it and set up disterbance,

You say it is only when mooving not when moored up so it sounds like there is nothing wrong with the drive chain.

Only a thought but worth looking at as you seem to have done everything else.