Can prop damage cause prop singing?

[nicknorman]

When our boat was new, it suffered from bad prop singing at normal canal cruising engine rpm of 1200-1400rpm. Fixed by dry docking and taking a grinder to the trailing edge of the blades. It’s been fine for the past 7 years. Just recently, we have started to get an annoying howl which is not identical in tone, but quite similar. And in the exact same rev range. Oddly it doesn’t immediately do it on setting it it cold, it starts after perhaps 5 mins. I have checked the gearbox alignment and whilst the drive was disconnected, felt the gearbox output bearing which was smooth and with no detectable play. Turning on the stern greaser doesn’t affect it and anyway I have adjusted the packing with no effect. So I am wondering if the prop singing has returned. It all started shorty after Minworth middle lock when once again we were aground and thrashing the engine over the pile of stones  with some clonking coming from the prop. I know that singing is normally an issue with a “perfect” prop and thatchunks out of it usually reduces any tendency to sing, but is it possible that an ill-placed notch could cause singing?

[Ray T]

Does it sing this song?

 

 

[Tony Brooks]

As its resonance I can' see why damage would not cause singing.

[WotEver]

WotEver’s little egg whisk sang and the next time it was docked we found it was both bent and had a chunk out of it. The yard swapped it for an identical (apart from the damage) one they had kicking around. No more singing. So that suggested to me that the damage was the cause. 

[nicknorman]

Ok thanks everyone. When we get back to the marina and once the water has settled clear, I’ll have a better look. I think I’d rather it was the prop than the stern tube or gearbox!

[X Alan W]

2 hours ago, nicknorman said:

Ok thanks everyone. When we get back to the marina and once the water has settled clear, I’ll have a better look. I think I’d rather it was the prop than the stern tube or gearbox!

Have a peer/feel down the hatch & feel the blade edges to ascertain any damage, a peer at the prop in "cleanish" water may let you see any problems+ an up/down pull/push on the prop will show any play in the stern bush & possibly show up if the props come loose after it"s stone chattering exercise

[nicknorman]

11 minutes ago, X Alan W said:

Have a peer/feel down the hatch & feel the blade edges to ascertain any damage, a peer at the prop in "cleanish" water may let you see any problems+ an up/down pull/push on the prop will show any play in the stern bush & possibly show up if the props come loose after it"s stone chattering exercise

Thanks, so far I have had a good pull on the prop, doesn’t seem to be loose, the split pin is still in and nut won’t turn by hand. When we had it out for blacking a couple of years ago, there did seem to be more than expected play in the stern tube once all packing and grease was removed, but it wasn’t horrendous. If it was some resonance of the prop shaft in stern tube I would have though a couple of turns on the greaser would have had some effect, even if only temporary.

 

Yes the prop has various small nicks and dents - from 7 years cruising in too-shallow canals, around the BCN etc - but it’s hard to know which if any might cause a problem.

 

[NB Esk]

A short piece of soil pipe or drain pipe, with a piece of glass or clear plastic bonded to one end with sealant, would allow you to closely inspect the prop.  A cheap waterproof torch taped to the end, and you have the deluxe version.

[Mikexx]

2 hours ago, nicknorman said:

Yes the prop has various small nicks and dents - from 7 years cruising in too-shallow canals, around the BCN etc - but it’s hard to know which if any might cause a problem.

 

 

Would it be possible to apply a file to the prop through the weed-hatch?

 

[nicknorman]

3 minutes ago, Mikexx said:

 

Would it be possible to apply a file to the prop through the weed-hatch?

 

Yes, however what sort of file? Presumably the prop is some sort of bronze, does it file easily? I have tried to file brass in the past, doesn’t really work! But maybe bronze is hard enough?

[Boat&Bikes]

42 minutes ago, nicknorman said:

Yes, however what sort of file? Presumably the prop is some sort of bronze, does it file easily? I have tried to file brass in the past, doesn’t really work! But maybe bronze is hard enough?

A big file!

[bizzard]

A big Bastard one.

[nb Innisfree]

Waterproof one. 

[Bee]

As you say new props often sing. Filing the edges is supposed to work but mine stopped after a while when it just got scabby with marine growth and green stuff. I expect you have picked up a few nicks with sharp edges on the stones and they have caused some sort of resonance, I would have a go with a file and see what happens - can't do much harm, I've never had a problem filing brass and bronze, I can't remember what alloy props are usually made of but it seems quite soft and bendy, good luck with it. (Oh, don't try putting the angle grinder down the weed hatch - Bad Idea)

Edited May 28, 2018 by Bee

[MtB]

41 minutes ago, bizzard said:

A big Bastard one.

 

All bastard files are big.

 

If it isn't big it isn't a bastard, Shirley.

[ditchcrawler]

1 hour ago, bizzard said:

A big Bastard one.

That's the one