Prop Shaft Noise

[pissativlypossed]

We have a strange high pitched whistling noise emenating from the stern of our boat, we are on shafts, and the noise starts when the shafts start to rotate, but it stops above 750 rpm. High speed running does not appear to be affected and the whistling is not present.
When we engage reverse the whistling is present but at a slightly different pitch and again up to about 750rpm.
The two main bearings are water cooled and are not getting hot and there does not seem to be any excessive vibration or movement in the shaft's.
The boat has done 105 hours and this noise has been getting progressivly louder the last 10 hours or so.
We do have Spur's rope cutters fitted.
The engines and gear boxes have just been serviced the engineer was happy that the problem was after the gearbox. The strange thing is that it is on both engines, I can understand if a cutlass bearing has gone where the noise is coming from, but 2 at the same time seems a little too coincidental.
Any ideas please?

 

[hlb]

Has the boat been out the water??

 

[pissativlypossed]

Yes, for antifoul and replacing anodes, not sure if this was when noise first appeared though.

 

[David_J]

You got it. Just been through this myself.
A little tube of blue Volvo grease. Think it was about 80p. Keep quiet though as I thought VP sold nothing for less than £50
Then helped a pal out of exactly same thing and felt all smug and knowledgable.
However did not feel so smug when I then developed an (unrelated) water leak from the engine. See new thread.
The worrying thing for me was that the dealer had the boat lifted out a few times in the first year and the people who did the work had no idea of bleeding or greasing the stern gland after every liftout.

 

[hlb]

It's a small world. We had the same problem for the firt time, last week with the barge. (Just back in water) It made an awfull racket. Not having a confuser handy I rang Tony Boatone and between us we sorted it out. You will probably have an air lock in the stern gland water way. I just took the pipe off, the water gushed out, then stuck it on again. Problem solved. Others apparently have a squeezy rubber thingy to press.

 

[David_J]

On my boat the stern gland is covered in a rubber moulding. Its easy, you just empty absolutely everything out of the lazarette, unscrew a wooden cover then hang upside down while griping/distorting the rubber like Arnie on a bad day untill a bit of water drips out. Then put blue grease on the special little split top hat section plastic applicator. Using the split pop it over the shaft and slide under the rubber and twizzle to transfer the grease to shaft and rubber. Easy,,,, oh, then spend half a day putting everything back. No wonder the dealers boys never bothered. But the engineer who showed me claimed it was an expensive killer if you dont do it after every lift out and at least every year. New stern gland jobbeee. It was actually done on mine as part of the routine service and I watched his every move to catch tips like this.

 

[pissativlypossed]

My stern glands are water cooled, by water pumped by the engine via a 1/2" (13mm) ish, rubber pipe, this exits from the transom and I always check before leaving the berth.
I am making the assumption that there is no other gland or shaft that requires attention before the boat is put back in the water. Am I making the correct assumption?

 

[David_J]

The stern gland on my boat is water cooled with a similar pipe connected to a sea cock. Better check if the type of stern gland fitted to your boat needs this bleeding and greasing procedure after lift out.

 

[blueglass]

I think I can help you relax on this one. You have what is called in the trade a "whistling propellor". We have the same problem, appearing in the very same rev band you have encountered. What happens is that a harmonic resonation is set up by the propellor presenting itself as a high pitched whine as you experience. The good news is that it apart from the irritating noise it is not harmful in any way, other than minutely diminished efficiency. The cure requires a lift ( I would do it next time you lift the boat for the winter rather than lift just for this) It's not a DIY job - you need a prop repairer - what they do is attach a small edge to one of the blades of the prop to alter its harmonic characteristics. Sometimes requires dropping back in/trial/adjustment.
The marine engineer I had look at it told me to use the boat normally for the season and have it looked at next time she was out. This was a second opinion by a professional as I wasn't really convinced by the first one!

 

[pissativlypossed]

Thank You All, I now feel a little bit more confident that the props are not going to drop off.

 

[hlb]

Not so fast. None of us know for sure what your problem is, only things to look at and address.

 

[pissativlypossed]

Thanks Hadyn, I feel much better now. I have asked Mountbatten boat house to have a quick look for me, I will let you know their report.

 

[hlb]

Arg!! Much easier to ring Merv the perv direct. Ask him when he's going to mend some of my oil leaks. /forums/images/graemlins/laugh.gif

 

[Deleted User YDKXO]

Same thing was happening to my boat from starboard prop at idle rpm. Prop was rebalanced and whistling has gone