high cutlass bearing wear

[voyager35]

on a fairly new to me boat I am getting excessive cutlass bearing wear. A new bearing was fitted this spring, and after around 100hrs of engine running it is noticeably more play in it.
The boat which weighs around 14 ton has a 50hp Beta engine running through quite a long 25mm propshaft. The inboard end is supported by a thrust bearing and the outboard end by a P bracket.
when i am motoring there is no noticeable or strange vibration from anywhere, but in gear at tickover RPM there is a horrible grinding/squeeking noise that is loudest above where the P bracket is located. The noise goes away at higher RPM.
The noise is probably worse in reverse and much worse plus lots of vibration when reverse is engaged to slow down the boat.
Because of the thrust bearing all seaming to be in good condition I think I can rule out a misalignment problem at the engine end.
Where the shaft seal is fitted about 300mm back from the thrust bearing i can see a tiny amount of movement in the prop shaft perhaps indicating that the shaft is distorted.
The only other thing that I have noticed which I dont think is in any way related is that there is a lot of cavitation noise from the prop when going into a short sharp sea

 

[Boater Sam]

on a fairly new to me boat I am getting excessive cutlass bearing wear. A new bearing was fitted this spring, and after around 100hrs of engine running it is noticeably more play in it.
The boat which weighs around 14 ton has a 50hp Beta engine running through quite a long 25mm propshaft. The inboard end is supported by a thrust bearing and the outboard end by a P bracket.
when i am motoring there is no noticeable or strange vibration from anywhere, but in gear at tickover RPM there is a horrible grinding/squeeking noise that is loudest above where the P bracket is located. The noise goes away at higher RPM.
The noise is probably worse in reverse and much worse plus lots of vibration when reverse is engaged to slow down the boat.
Because of the thrust bearing all seaming to be in good condition I think I can rule out a misalignment problem at the engine end.
Where the shaft seal is fitted about 300mm back from the thrust bearing i can see a tiny amount of movement in the prop shaft perhaps indicating that the shaft is distorted.
The only other thing that I have noticed which I dont think is in any way related is that there is a lot of cavitation noise from the prop when going into a short sharp sea

With a 50HP 4 cylinder Beta engine running on a thin 25mm diameter long shaft into a P bracket I would expect either shaft or P bracket is distorted or even both.

 

[lusitano]

Depending on the boat, shaft alignment in and out of the water can differ, even when a support bearing is involved.
Symptoms certainly point to shaft out of kilter.
Start with the basics first - alignment check - in the water after settling and a few minutes running in gear, ahead and astern - disconnect shaft at the gearbox coupling and slide shaft back just a tad - measure gap using feeler gauge. Rotate shaft 90/180/270 degs, measuring at each point
(Mark shaft before disconnecting)

 

[Tranona]

Is that 25mm shaft original? What was the original engine? as a 25mm shaft is far too small for a 14T boat with a 50hp engine.

I have just re-engined a boat with a 30hp rather than the original 20 (which was underpowered) with a long (53") shaft and despite having an intermediate bearing we went for a 30mm shaft instead of the original 1".

So suspect the problem is the shaft distorting. Difficult to comment on the noise and cavitation without seeing the set up, but presumably the big engine has a large(r) diameter propeller and there is a tip clearance problem.

Details of the boat and photos of both the inside and outside would be helpful.

 

[Bilgediver]

With a 50HP 4 cylinder Beta engine running on a thin 25mm diameter long shaft into a P bracket I would expect either shaft or P bracket is distorted or even both.

I wonder what size prop is that wee 25mm shaft trying to swing.

 

[Tranona]

Probably 18 or 19" diameter!

 

[Bilgediver]

Probably 18 or 19" diameter!

A torsional analysis might give interesting readings

 

[Supertramp]

10t boat, Beta 60, similar set up with thrust bearing, 35mm shaft.

25mm seems very undersized. However that is probably how the boat was set up. Was it re-engined with lots more power?

Definitely check the shaft and replace if not true - increasing the shaft diameter would be a significant job and cost.

 

[Tranona]

25mm seems very undersized. However that is probably how the boat was set up. Was it re-engined with lots more power?

That was my initial thought but if anything a 50hp is underpowered for a 14T boat. Difficult to make any serious observations without more information.

 

[voyager35]

I have just realised that I have given the wrong shaft size IT IS 1 1/4 INCH 32 MM

 

[vyv_cox]

Is the shaft central in the stern tube? This needs to be the first action when aligning the engine. Small wooden wedges between shaft and tube at 90 degrees intervals with the coupling bolts undone. Then bring the gearbox flange to the shaft flange and align to just a few thou (inch) vertically and horizontally.
It sounds probable that your shaft is hitting the tube under some conditions.
What do you mean by a 'thrust bearing'? Is this a flexible coupling? More info needed.

 

[Tranona]

OK that is the minimum for 50hp depending on how long the unsupported shaft is. There clearly seems to be something wrong if there are noises as you describe, but it is likely to be at the P bracket end. Do you know how much clearance there is between the P bracket and the front face of the propeller? do you have a rope cutter fitted?. A photo of the stern gear would help understand what to look for.

 

[david_bagshaw]

I would check the p bracket, is not twisted to the shaft. the noise suggests some angular miss alignment. of the cutlass.

 

[voyager35]

Is the shaft central in the stern tube? This needs to be the first action when aligning the engine. Small wooden wedges between shaft and tube at 90 degrees intervals with the coupling bolts undone. Then bring the gearbox flange to the shaft flange and align to just a few thou (inch) vertically and horizontally.
It sounds probable that your shaft is hitting the tube under some conditions.
What do you mean by a 'thrust bearing'? Is this a flexible coupling? More info needed.

There is a small bulkhead about 9inches behind the gear box. A bearing housing is bolted to this which has a cv type joint that is taking up the different angle between the engine and the prop shaft and appears to be taking the forward thrust from the prop instead of it being transmitted through to the gear box.
it looks similar to an aquadrive unit

 

[voyager35]

OK that is the minimum for 50hp depending on how long the unsupported shaft is. There clearly seems to be something wrong if there are noises as you describe, but it is likely to be at the P bracket end. Do you know how much clearance there is between the P bracket and the front face of the propeller? do you have a rope cutter fitted?. A photo of the stern gear would help understand what to look for.

There is 20-25mm between the blade type rope cutter and the back of the P bracket.
I need to dry the boat out and have a better look, when i dried out last week the boat sank into the mud to above prop level which was rather frustrating

 

[Tranona]

That is typical to allow movement fore and aft of the shaft when going in and out of gear while allowing flow of water through the cutless. However if your shaft goes into a thrust block as you describe there should be no movement at all.

 

[Graham376]

Our shaft is 1 1/4" and a replacement Vetus cutless bearing only lasted a couple of years and when I bought a replacement, turned out it was oversized ID. Changed for a Countrose which was tighter fit and that's been fine for a few years.

 

[voyager35]

Our shaft is 1 1/4" and a replacement Vetus cutless bearing only lasted a couple of years and when I bought a replacement, turned out it was oversized ID. Changed for a Countrose which was tighter fit and that's been fine for a few years.

when the new bearing was fitted by an engineer down in Devon there was still a small amount of movement in the shaft. He was addiment that it was the correct bearing but I hade my doubts ( I wasnt paying for the work).
was the Countrose bearing polyethene or the nitryl ?

 

[Tranona]

1 1/4" is a unique size, that is there is no close metric equivalent unlike for example 1"/25mm or 1 3/8" 35mm so the chances of it being "too big" are not high. the bearing material does not normally make any difference to clearance or to bearing life.

 

[Graham376]

when the new bearing was fitted by an engineer down in Devon there was still a small amount of movement in the shaft. He was addiment that it was the correct bearing but I hade my doubts ( I wasnt paying for the work).
was the Countrose bearing polyethene or the nitryl ?

I can't remember which I bought, invoice is at home. I was offered choice of two, one being harder material than the other.