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Whining high pitch noise - is it Prop Singing?


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Hello Everyone,

 

We have a 65 ft narrowboat with a isuzu marine 42 engine.

 

Our issue is that when moving at a certain speed (not sure the exact rpm as our rev counter is broken ) we hear a high pitched noise coming from our engine bay? if we go faster or slower it goes away. I have checked the alternator belts but they seem fine and it doesn't make this sound when we are out of gear and we rev the engine moored.

 

I think it sounds like prop singing from other forums. I would love some advice if it prop singing or  if anyone knows if it could be something else? Should i be worried that it is doing damage?

 

Thank you!

Edited by DannyboatVictoria
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I don't think anyone can say with certainty that it is prop singing  but if it is, it is unlikely to do any actual damage. If it's a growling sound it could be cavitation and that can do damage. Make sure its not the anti-caviation plate that often hangs down from the weed hatch vibrating against the trunk.

 

The usual cure is to grind the prop edges to a certain profile, but its a bit of a black art.

 

 

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Has it always done this or is it a recent change?

 

I had a hash buzzing noise that recently occurred at a repeatable fairly narrow rpm band.  After spending a fair bit of time checking lots of nuts & bolts etc, I checked the prop.  There was a big ding on the tip of one blade, sort of torn and folded at right angles, say 12x5mm.  Filed off the projection and all back to normal.  
 

If you do check the prop blades for damage that can cause the blade to resonate, take care (wear cut proof gloves) as my ding was sharp enough to cut, and canal water and cut fingers are not a god combination.

Edited by Chewbacka
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19 minutes ago, Tony Brooks said:

I don't think anyone can say with certainty that it is prop singing  but if it is, it is unlikely to do any actual damage. If it's a growling sound it could be cavitation and that can do damage. Make sure its not the anti-caviation plate that often hangs down from the weed hatch vibrating against the trunk.

 

The usual cure is to grind the prop edges to a certain profile, but its a bit of a black art.

 

 

 

It definitely doesn't sound like growling more of a wheeeeeeee at a constant pitch

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45 minutes ago, Bee said:

Hard to say. Our prop sings, its a bit like a slightly wobbly tuning fork noise, G Major I reckon, Son reckons its nearer F.

 

Get a tuning fork. or a frequency analyser, or any stable musical instrument (ie not stringed).

 

A is 220 or 440 Hz in modern concert pitch (at the two most likely octaves).

G is about 196 or 392 Hz.

F is a bit under 175 or a bit over 349 Hz.

(All in equal temperaent, of course).

 

 

 

 

You might then be able to relate the frequency to the propeller rotational speed and number of blades.

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I'm gonna guess in dark that it's a prm, solely based on the prm stamped on the side.

 

Have you just acquired the boat or changed the prop ? Or have you had it for a while and it's just started.

 

May need the propellor edge chamfered to a point.

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I once suffered a loud clonk going under a bridge (not the sort of urban bridge hole which warrants cruising through in neutral) after which my prop began to sing.  A couple of minutes down the weed hatch dressing a small dink in the prop fettled it. Worth rolling up a sleeve and feeling the prop blade edges - be careful though as canal water isn't the cleverest medium in which to give yourself lacerations! 

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14 hours ago, Paul&Sam said:

I'm gonna guess in dark that it's a prm, solely based on the prm stamped on the side.

 

Have you just acquired the boat or changed the prop ? Or have you had it for a while and it's just started.

 

May need the propellor edge chamfered to a point.

 

We have had the boat for a year. And kept it moored in a marina over winter. It's pretty much always been happening. 

 

For a while i thought it was an alternator belt and we have tightened them and loosened them and all sorts but it still happens. It is also only happens when moving forward (doesn't happen in reverse) 

 

 

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On 16/06/2021 at 18:14, Tracy D'arth said:

PRM 150 or maybe a Delta, hydraulic box, unlikely to make much noise, if its short of oil it will lose drive. Look elsewhere for the noise. How loud is the noise? any chance of a recording being posted?

 

Looks very much like my PRM150, except that the engine marinator has painted it blue, not green.

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36 minutes ago, Machpoint005 said:

 

Looks very much like my PRM150, except that the engine marinator has painted it blue, not green.

I suspect that -- unlike the pork for tonight's vindaloo -- the engine has not been marinated but marinised... ?

Edited by IanD
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