Unbalanced prop, bent shaft?

[MASH]

My Sadler 32 seems to eat cutlass bearings. How does one check for an unbalanced prop or an out of true shaft? Is this likely to be the cause? If not, what else is?

In Turkey?

(ie, is there a way I can check it myself - and if so what is an acceptable tolerance in shaft and prop?)

 

[bigman1]

re unbalanced shaft

check your shaft when under way(very careful no loose clothing ect.)there should be no out of true movement,if there is then the shaft is bent,when engine is shut down grip shaft near stern gland and try to move it in the vertical and horizontal plane,there should be very little or no movement about ten thou.is ok 1/16"too much,new bearing required,if shaft is bent,when ashore remove it and take it to a machine shop they may be able to straighten it,but more than likely a new shaft will be required.All the best.Ronnie.

 

[Paul1962]

Hi,
Unless you have some serious vibration when underway using engine, I think you may be able to discount a bent prop or shaft.
If this is the case then I would suggest the water you are using the vessel in is grit/sand contaminated. In which case, you will have to live with the life of your cutlass bearings.
What sort of life are you getting anyway??
Just my thoughts.

Regards

 

[Bosun Higgs]

What happens to the bearings? Do they wear in one plane ( as mine do) or is the wear round the full 360. And do you have vibration?

If they wear in one plane its more likely that the engine alignment is an issue - a bent shaft will wear the bearing through 360.

Get the boat going under sail with the engine off and out of gear. If the rotating thaft is moving the engine on its mounts there is a problem. If the shaft is moving more in the middle than the end, shaft straightness.

The only way of telling if a shaft is bent is to remove the shaft and get it put on a lathe with a dial guage - which should be easily and cheaply done in Turkey. They can be straightened. I once watched a toolmaker do that to one of my shafts by leaning on it . Mind you he was a fat barsteward.

 

[Onyva]

My understanding is that sand & grit are the true CB eaters.....

 

[vyv_cox]

My understanding is that sand & grit are the true CB eaters.....

Correct. I wore one out in eleven days through the Canal du Midi.

 

[Tranona]

Correct. I wore one out in eleven days through the Canal du Midi.

Yes, but this boat is in Turkey! where I suspect the water is very clean (silt wise).

Usual suspects are mis-alignment, bent shaft, worn shaft. loose P bracket.

 

[Neil_Y]

Another common but often neglected problem can be carrier misalignment.

The P bracket could be out of true, this can happen if debris has ever been caught round the prop.

You can usually see this with the boat out of the water as the gap should be above the shaft as it sits down in the bearing under its own weight, any gap that is at its maximum at any other position can indicate bent shaft or misaligned carrier.

To check for alignment use a clearance fit bearing and dry assemble shaft and bearings, check with feeler guage that clearance is at the top of the bearing. You can also chock the shaft and you should be able to spin the bearings on the shaft and in the carrier, this confirms carrier shaft alignment. You can the n move on to alignment of the engine to the shaft.

Sand and silt will effect wear and there are a number of opinions as to which is the best material for the bearing surface to get longer life from them. I could be considered as biased so will leave you to do your own research.