Prop damage

[Farey]

I discovered some damage to my prop (it's an Axiom, fitted in 2011, but I'm not looking to start another discussion on Axiom props). A small chunk, about 1 x 3 cm, is missing from one blade. I haven't noticed any significant  vibration, but am concerned that it may unbalance the prop and put extra strain on the prop shaft and bearing. Any views?

[Guest]

You say no 'significant' vibration, which implies there is some.

 

Has this increased or appeared suddenly?

 

I would be concerned if it has, for the reasons you suggest.

[Machpoint005]

If there is no significant vibration, there is no significant imbalance.

 

If there is, there is,

[Tracy D'arth]

Selective rectangular monoblade  cavitation corrosion. If yours is a 4 cylinder engine, one cylinder is running faster than the others.  

Ita a 4 bladed prop on a 4 cylinder engine?

That's why proper props are 3 bladed.

Edited September 22, 2020 by Tracy D'arth

[smiler]

1 minute ago, Tracy D'arth said:

Selective rectangular monoblade  cavitation corrosion. If yours is a 4 cylinder, one cylinder is running faster than the others.

?????????

[Alan de Enfield]

1 hour ago, Tracy D'arth said:

If yours is a 4 cylinder engine, one cylinder is running faster than the others.  

Not quite sure how that works - are all 4 pistons not all connected to the same crankshaft ?

[Machpoint005]

1 hour ago, Tracy D'arth said:

If yours is a 4 cylinder engine, one cylinder is running faster than the others.  

 

Er, no it isn't.

 

 

[Guest]

2 minutes ago, Machpoint005 said:

 

Er, no it isn't.

 

 

I think it was an attempt at humour........

 

Given it's a mechanical impossibility.

[Machpoint005]

If you only think so, that's a good indication that it wasn't humour!

[Guest]

1 minute ago, Machpoint005 said:

If you only think so, that's a good indication that it wasn't humour!

Not really.

 

As the things people find funny often differ, sometimes quite widely.

 

This place is littered with examples.

[beerbeerbeerbeerbeer]

7 minutes ago, The Happy Nomad said:

I think it was an attempt at humour........

 

Given it's a mechanical impossibility.

Probably got some folk googling it though. 
 

 ?

 

 

[Machpoint005]

Given that it was the OP's first post, I think he deserved sensible answers.

[Guest]

Just now, Machpoint005 said:

Given that it was the OP's first post, I think he deserved sensible answers.

I agree actually.

 

(But it's not his first post, it's his 121st)

[Machpoint005]

So it is, my mistake!

[Mad Harold]

2 hours ago, Tracy D'arth said:

Selective rectangular monoblade  cavitation corrosion. If yours is a 4 cylinder engine, one cylinder is running faster than the others.  

Ita a 4 bladed prop on a 4 cylinder engine?

That's why proper props are 3 bladed.

One cylinder can run faster if one big end journal has been reground in isolation,giving a slightly different throw and therefore a different piston speed.

As for the selective rectangular monoblade cavitation corrosion,that will only occur if you have a goniometer fitted to your solar panel.

By the way,what brand of beer do you drink?

 

[Guest]

5 minutes ago, Mad Harold said:

One cylinder can run faster if one big end journal has been reground in isolation,giving a slightly different throw and therefore a different piston speed.

I don't think it would work like that would it.

 

If you grind the journal in isolation (not good practice I would think) you compensate with over size bearings. This would set the throw back to what it was originally, surely?

[Tony Brooks]

3 hours ago, Farey said:

I discovered some damage to my prop (it's an Axiom, fitted in 2011, but I'm not looking to start another discussion on Axiom props). A small chunk, about 1 x 3 cm, is missing from one blade. I haven't noticed any significant  vibration, but am concerned that it may unbalance the prop and put extra strain on the prop shaft and bearing. Any views?

 

I think that if you can't detect any more vibration of weird noises then as long as the shaft has a plain metal bearing and greaser (not a rubber Cutless bearing or fibre/paxalon bearing) you have little to worry about. I am not sure if you could find a prop re furbisher to take it on though.

[David Mack]

1 hour ago, The Happy Nomad said:

I think it was an attempt at humour........

 

Given it's a mechanical impossibility.

And doesn't take into account that most boats have a gearbox with a reduction ratio that is not 1:1.

[Machpoint005]

1 hour ago, Mad Harold said:

>>giving a slightly different throw and therefore a different piston speed.<<

 

But exactly the same rotational speed.

[Farey]

Thanks for the various answers. To clarify, it is a Volvo Penta cutless bearing, and the prop has 3 blades, and although I don't post very often, I've been a member since 2005.

Edited September 22, 2020 by Farey
Add info

[Tony Brooks]

Just now, Farey said:

Thanks for the various answers. To clarify, it is a Volvo Penta cutless bearing, and the prop has 3 blades.

Those bearings are normally replaceable so maybe it will just shorten the replacement intervals 

.