Prop shaft - what is this attached on it?

[moiuk]

Can anybody help me understand what this circular ring is attached to my prop shaft?

 

 

 

 

[mrsmelly]

Looks like a centaflex type coupling?

[ditchcrawler]

Its a flexible drive coupling I have one exactly like it. Proper name a Fenerflex split coupling

Edited April 19, 2022 by ditchcrawler

[Guest]

22 minutes ago, moiuk said:

Can anybody help me understand what this circular ring is attached to my prop shaft?

 

 

 

 

 

Looks like a vibration/torque dampener.

Edited April 19, 2022 by The Happy Nomad

[moiuk]

Just now, mrsmelly said:

Looks like a centaflex type coupling?

What's it's purpose? And is it supposed to have a crack/space in it as shown in the photo?

[mrsmelly]

Just now, moiuk said:

What's it's purpose? And is it supposed to have a crack/space in it as shown in the photo?

They reduce noise and vibration. The crack is probably just a join, it looks in good order from that foto?

[ditchcrawler]

1 minute ago, moiuk said:

What's it's purpose? And is it supposed to have a crack/space in it as shown in the photo?

It connects your prop shaft to your gear box to provide a flexible drive and yes the space is meant to be there  

 

[mrsmelly]

Think of it like a cush drive but different.

[beerbeerbeerbeerbeer]

It’s a Fenner tyre.

I have one, it’s a flexible coupling

If ever you come to change it you will realise it has a split so it can slip over the plates that hold it tight

 

 

and as mrsmelly says it acts like a cush drive too

Edited April 19, 2022 by Goliath

[ditchcrawler]

Just now, ditchcrawler said:

It connects your prop shaft to your gear box to provide a flexible drive and yes the space is meant to be there  

 

Quote

Tyre Couplings from Fenner Power Transmissions (fptgroup.com)

 

[MtB]

7 minutes ago, moiuk said:

What's it's purpose? 

 

No-one has explained the real reason so far so I'll have a go.

 

These are usually fitted when the engine is on flexible mounts. If there was no flexible joint in the prop shaft, the prop shaft would try to rigidly hold the engine in perfect alignment which would result in heavy wear in the stern tube and stern gland. It's a bit of a bodge really as to truly decouple engine movement on its mounts from the stern gland, two flexible joints separated by a short shaft would be necessary. 

 

 

[beerbeerbeerbeerbeer]

Works surprisingly well for a bodge.

So I wouldn’t worry. 

[moiuk]

Thank you everybody 😊

[David Mack]

12 hours ago, MtB said:

 

These are usually fitted when the engine is on flexible mounts. 

They were also fitted to Big Woolwich boats (and maybe others), even though the engines were rigidly mounted.

 

12 hours ago, MtB said:

It's a bit of a bodge really as to truly decouple engine movement on its mounts from the stern gland, two flexible joints separated by a short shaft would be necessary. 

The Fenner couplings claim to cope with lateral as well as angular misalignment.

[Bee]

I have one, they are good things but will not take thrust hence what looks like a hefty thrust bearing just behind it, As others have said it is saving the gearbox rear bearing and thrust bearing from stress and wear when the engine moves on its mounts.