Shaft or propeller knock

[colin.marshall]

My colvic countess 28 developed a knocking from aft area only when in gear. With gopro I have confirmed my shaft anode has fallen off so at least I know its not that,
I was also able to video and slow down the motion of the prop. I can see quite a bit of movement in shaft and hoped for some opinions on what root cause is.


Can i add video?

 

[peteK]

Worn cutlass bearing.

 

[colin.marshall]

Thanks for reply. I did think so but would like to share a video. Can i add to youtube and share a link?
Is it likely that there has been something which caused this, or just something that happens?

I am wondering if its a bad engine mount, poor alignment or something else i can check before I lift it out? Though accept I will need to lift out anyway. I also don't have enough experience to know how bad this is vs others. (though can be sure its not right)

 

[colin.marshall]

Thanks for reply. I did think so but would like to share a video. Can i add to youtube and share a link?
Is it likely that there has been something which caused this, or just something that happens?

I am wondering if its a bad engine mount, poor alignment or something else i can check before I lift it out? Though accept I will need to lift out anyway. I also don't have enough experience to know how bad this is vs others. (though can be sure its not right)

 

[colin.marshall]

 

[lusitano]

Looking at the video, it does indeed look like the shaft is flopping around badly.
You need to change the cutlass bearing before you can accurately align the shaft to the engine/gearbox assembly

 

[colin.marshall]

Looking at the video, it does indeed look like the shaft is flopping around badly.
You need to change the cutlass bearing before you can accurately align the shaft to the engine/gearbox assembly

I was surprised to see same movement when rotating prop by hand. Made me wonder if shaft was actually bent.

 

[Tranona]

Cutless bearing worn. Probably because whoever installed that shaft and prop left far to much exposed shaft resulting in the shaft whipping. 1.5* diameter is the rule of thumb, so around 40mm, and guess that ia around 70mm+.

You may well need a new shaft as suspect there will be wear at the point it goes through the now worn out bearing. If shaft OK, then have it shortened at the gearbox end.

 

[colin.marshall]

Here a slowed down video of coupling to engine.

 

[cherod]

that is pretty bad, might be worth checking the run out once you have fitted a new bearing .

 

[cherod]

Here a slowed down video of coupling to engine.

i would say that the shaft looks alright . , although there does seem to be a little movement in the rubber , i dont know if that is within tolerances .

 

[Deleted member 36384]

You have a skeg, so you have to remove the engine to get the propellor shaft out? If so take all measurements now so that you can confidently reduce the propellor size.

Also, if you do have to remove the engine, consider fitting a CV joint Aquadrive Antivibration System | Halyard | Make Boating More Enjoyable You might not have enough space for a CV joint.

It would make engine alignment very easy. I bent my propellor shaft, have a skeg and had to remove the engine. Fitted a CV joint which reduced vibration and made alignment easy. Something to think about.

 

[cherod]

You have a skeg, so you have to remove the engine to get the propellor shaft out? If so take all measurements now so that you can confidently reduce the propellor size.

Also, if you do have to remove the engine, consider fitting a CV joint Aquadrive Antivibration System | Halyard | Make Boating More Enjoyable You might not have enough space for a CV joint.

It would make engine alignment very easy. I bent my propellor shaft, have a skeg and had to remove the engine. Fitted a CV joint which reduced vibration and made alignment easy. Something to think about.

or use a grinder instead of removal ( why would he reduce the propellor size , do you mean propshaft ? )

 

[Deleted member 36384]

or use a grinder instead of removal ( why would he reduce the propellor size , do you mean propshaft ? )

Yes I meant propellor shaft, thanks for picking up on that. Use a grinder for what?

 

[cherod]

Yes I meant propellor shaft, thanks for picking up on that. Use a grinder for what?

to shorten the shaft ( at the gearbox end )

 

[colin.marshall]

It had occurred to me that lifting the engine to get shaft out might be required. That could be a post on its own....

Appreciate the advice

 

[colin.marshall]

I found this very short video of the shaft and prop out of water. You can see that there was just enough room to fit the anode. Are we still thinking shaft is too long?

 

[Tranona]

Yes, the shaft is too long and having that heavy lump of anode will not have helped. Shaft anodes are not designed for this type of set up but for P bracket stern gear where there is exposed shaft ahead of the P bracket. The anode is mounted there. If you want an anode then you have a choice of a prop nut anode, or more commonly a pear shaped hull anode bonded to the shaft through the gearbox housing and a bridge across your flexible coupling.

Would guess the boat has been re-engined at some point so you may well find other installation details need looking at!

 

[colin.marshall]

Yes, the shaft is too long and having that heavy lump of anode will not have helped. Shaft anodes are not designed for this type of set up but for P bracket stern gear where there is exposed shaft ahead of the P bracket. The anode is mounted there. If you want an anode then you have a choice of a prop nut anode, or more commonly a pear shaped hull anode bonded to the shaft through the gearbox housing and a bridge across your flexible coupling.

Would guess the boat has been re-engined at some point so you may well find other installation details need looking at!

Thanks. This was as found I.e. when bought earlier this year. The advice about anode makes perfect sense as a friend did wonder how it could be balanced with an anode thrown on there.
I know that it was re engined, about 20 yrs ago off the top of my head, from the paperwork I have. It was supplied and fitted by the engine dealer. Its a lister petter lpw3.
I'll maybe get some to have a look at full set up but welcome any suggestions on main things to check. I'll browse the archives too.
I'm in Scotland on the Clyde at greenock if anyone can recommend a good engineer....

 

[bignick]

Hopefully you will find that the propeller skeg is actually 40mm or so off to one side, so that the prop shaft clears the rudder skeg. It’s very common, but I can’t be absolutely sure for your boat. Designers and marine engineers do tend to think about these things, or should do!