Prop Shaft Squeak


ngtnewington Newington
 

Hi James,

Since you plan to pull the shaft and check it at a machine shop you should also check that the prop is true. Many years ago (1991) I had a similar problem, it was on my first boat a 35’ gaff cutter. In Venezuela I installed a new engine, but the whole drive train was never checked. By the time I arrived in New Zealand I had only put on 200 hours as there was obviously a problem. Anchored off Russel in the Bay of Islands I pulled the prop and shaft, bunging the hole from inside and out. The machine shop right there checked the shaft, and it was bent. He checked the prop and it was true but completely the wrong prop for the type of boat. At very reasonable cost he supplied me with a second hand shaft and a second hand prop. I then went to town on the alignment and got it spot on. From that moment on engaging gear was a silky smooth transition and gradually powering up and loading the engine was a joy.

The point being that the whole power train from engine to prop is critical. I suggest in addition to checking the shaft, you have the prop checked for balance.

As James on Sueno says, the cutlass bearing might need “bedding in”. It should not be tight. It should be only bearing on the bottom due to the weight of the shaft with a very slight gap above and around. So there is a tiny bit of wiggle and you should be able to turn it by hand easily.

The alignment:

I see the shaft alternator and coupling arrangement from your photos. I suggest that initially you slide on the temporary nylon bearing down the shaft so that it sits in the stern tube and the shaft is then supported for and aft with minimal wiggle. Then gently slide the shaft forward so that it kisses the coupling. If it slides perfectly into the coupling slot without pushing it up or down or to one side then the alignment is already pretty good. 
I would then using feeler gauges check the alignment on the coupling to the transmission whilst rotating it. I am not sure that you actually need to remove the alternator pulley. If you want to, then the shaft should reach with the prop removed. 

I have said that the alignment is critical. However given the fact that there is no bearing forward, only a piece of exhaust hose and a lip seal that can move about quite freely, and given that the cutlass bearing must be at least three or four feet aft of the engine and the cutlass bearing is maybe five inches long. Also given the fact that the engine is mounted flexibly. I would say that the alignment needs to be such that the shaft slides without force into its coupling would be good enough. In my story above the engine was solidly mounted on hardwood blocks and there was a grease gland bearing at the forward end of the shaft. Alignment was very very critical. In your case it will not be so critical. I still think however that the technique to centre the shaft with a temporary nylon bearing is a great way to get the proper datum from which to work.

Regarding the squeak being between 1500-1800 rpm. It would not surprise me if either the prop or the shaft, or indeed alignment is the problem, or even all three.

Nick
Amelia AML 54-019
Kilada Greece


On 25 Nov 2019, at 00:50, James Lochhead <j_lochhead@...> wrote:


-- Thanks Nick.  Your description is perfect.  I will have another go at the alignment.  Due to location and with no assistance around at the time I did it myself with only advice from other cruisers.

It is out of the water currently so I will try your proposal of the temporary bearing while out first when I get back to the boat and then check again once I get back in the water.  Will also get the prop shaft checked.

I have one other question if you could help.  Due to the prop shaft generator the belt pulley sits between the vetus coupling and the transmission.  I have attached some photos from another post that shows the arrangement.  from memory the 4 bolts shown on the photo "vetus coupler" bolt through the coupling and the pulley holding it all in place.
When measuring the the alignment access to the back of the transmission is limited due to the generator pulley.  I am not sure if there is enough length in the shaft to pull it forward without the pulley in place.  Do you have any thoughts on this?

Also it is only at certain revs that the squeak was occurring.  Very low revs and then between 1500-1800.

James
Maramu #147 (1984) <Prop Shaft Alternator.jpg><Coupling.JPG><Vetus coupler.jpg>


James Alton
 

James,

    I thought of one more thing that possibly could be causing the noise.  I installed a cutlass bearing once that was a bit on the tight side,  apparently a manufacturing issue.  The Cutlass bearing made what I would call a “chirping” noise for while as it wore in.  Might be worth spinning the prop before you launch and listen for noise from the new cutlass bearing.

   Best of luck in solving the mystery squeak,  let us know what it turned out to be. 


Best,

James
SV Sueno
Maramu #220

On Nov 24, 2019, at 8:52 PM, James Lochhead <j_lochhead@...> wrote:

Thanks James,  I used your easier method last time.  Might try the "fancy" method now as it did not solve the issue.   Then if it continues at least I know it is not that.
--

James
Maramu #147 (1984)


James Lochhead
 

Hi Dennis,

Yep tried that.  I need to do a rebuild on the alternator anyway.  Did you have any issues sourcing the bearings?
--

James
Maramu #147 (1984)


James Lochhead
 

Thanks James,  I used your easier method last time.  Might try the "fancy" method now as it did not solve the issue.   Then if it continues at least I know it is not that.
--

James
Maramu #147 (1984)


James Lochhead
 


-- Thanks Nick.  Your description is perfect.  I will have another go at the alignment.  Due to location and with no assistance around at the time I did it myself with only advice from other cruisers.

It is out of the water currently so I will try your proposal of the temporary bearing while out first when I get back to the boat and then check again once I get back in the water.  Will also get the prop shaft checked.

I have one other question if you could help.  Due to the prop shaft generator the belt pulley sits between the vetus coupling and the transmission.  I have attached some photos from another post that shows the arrangement.  from memory the 4 bolts shown on the photo "vetus coupler" bolt through the coupling and the pulley holding it all in place.
When measuring the the alignment access to the back of the transmission is limited due to the generator pulley.  I am not sure if there is enough length in the shaft to pull it forward without the pulley in place.  Do you have any thoughts on this?

Also it is only at certain revs that the squeak was occurring.  Very low revs and then between 1500-1800.

James
Maramu #147 (1984)


sbmesasailor
 

Hi James,

I believe you have a shaft alternator right?  Try disconnecting the belt and see if the squeak stops.  We had a squeak and it was the alternator bearings.

Dennis
Libertad
Maramu #121


James Alton
 

James,

   I replaced the original Amel engine mounts on my Maramu #220 this year.  The part you have circled is the bronze stern tube which will extend into the hull.  It appeared that mine was bonded and glassed into the hull, it needs to be a rigid connection.  The stern tube provides the attachment for the short pc.  hose that the stuffing box gland attaches to, it is not supposed to be a bearing.  There should be relatively even clearance between the stern tube and the shaft which allows for some engine movement without the shaft touching anywhere.  As I understand things the cutlass bearing on our boats forms the aft bearing and the transmission bearing provides the front bearing to support the shaft.  Nick already mentioned the two most likely causes of your squeak but I will try to elaborate a little more.  Engine alignment is more than just getting the two faces of the coupling mated within a few thousandths, you also need to position shaft so that it is riding close to the center of the bronze stern tube so that it cannot touch.  The fancy way to set up this alignment is to remove the stuffing box and the short pc. of  hose and fit something solid like round rod of the right OD to hold rigidly hold the shaft in the very center of the stern tube, then to adjust your engine so that it is the correct height and also correctly positioned Port and Stb.  Once this is done you can do your actual alignment to get the coupling faces aligned.  An easier method that seems to work fine and can be done in the water is to decouple the shaft and by HAND force the shaft coupling to go as far as it will go up down and Port/Stb.  You will feel solid contact as you force the coupling to it’s limits as it touches the inside of the stern tube.  Note the relative displacement of the couplings to Port/Stb. and Up/Down and adjust the engine so that the displacement is the same top and bottom and side to side which will put the shaft pretty close to the center of the hole in the stern tube.  Once this is done,  align your coupling faces.  Also I initially only did a rough alignment on my engine because I knew that the new mounts would settle a bit and they did.  So after 50 hours I did a second alignment and sure enough the whole engine had settled a bit so brought it up.  

   As to the other possible causes of the squeak,  as Nick alluded is that the shaft could be bent.  You can often tell this when sailing with the engine off and the wheel turning.  If the back of the engine is moving around much in time with the shaft rotation, you could have a bent shaft,  if it is nice and smooth then probably not.

   One final possible cause of a squeak can be from having the stuffing box too tight.  With the new teflon packings you can pretty much tighten to the point where you don’t have any leakage but if you go too far the box begins to heat up, grab and squeak.  

Best of luck,

James Alton
SV Sueno
Maramu #220
Preveza,  Greece


On Nov 23, 2019, at 11:35 PM, James Lochhead <j_lochhead@...> wrote:

HI,

The attached photo is of the stuffing box and where the shaft on my maramu exits the boat.  Is the circled part another bearing that is glassed into the hull?

We have a "sqeak" or hum when the prop shaft is spinning at certain revs (both with engine and when sailing and free spinning) that we have not been able to diagnose.

The problem started following the failure of our engine mounts.  The engine mounts have been replaced and the cutless bearing was replaced at next haul out, however a squeak has remained on our last short cruise before hauling out again.  I have checked the engine alignment, the stuffing was replaced, but the squeak remained.

We will be back on the boat again in the new year and would like to eliminate the cause for this before going back in the water and if this is a bearing then possibly order one now.

--

James
Maramu #147 (1984) <Shaft photo.pdf>


ngtnewington Newington
 

Hi James,

1.  If the boat is ashore I would check that the shaft is true. You would need to pull it and take it to a machine shop.

2. I would check the engine alignment again. It is not easy to get spot on. One of the tricks I have learned is to decouple the shaft from the transmission and centre it within the stern tube. Then align the engine to the shaft.

On some systems the shaft is floating around and can be moved a lot as there is no bearing at the engine end of the stern tube. This would be the case with a modern drip free lip seal style stern gland. From the photo I think this is what you have. If there is shaft wiggle then make up a nylon bearing that slots into the stern tube at the front end, this involves removing the shaft seal, and sliding the nylon bearing over the shaft and into the stern tube. So there is a cutlass bearing aft and another nylon temporary bearing forward. This then centres the shaft spot on within the stern tube. With the shaft centred you then align the engine to it. It needs to be spot on. Then obviously remove the temporary nylon bearing, and put back the shaft seal.

The problem is that  it is much easier to do out of the water but the hull may take up a slightly different shape ashore, although if it has been carefully chocked and is nice and level a solid hull like a Maramu will probably not move much.

If in the water, I have used a  greased tape or plastic wrapped around the shaft and pushed into the cutlass bearing to reduce the flow. This works quite well, but water leaking into the boat adds a bit of stress.

There are other techniques, but this is my preferred.

Nick

S/Y Amelia AML 54-019
Kilada Greece.




On 24 Nov 2019, at 03:35, James Lochhead <j_lochhead@...> wrote:

HI,

The attached photo is of the stuffing box and where the shaft on my maramu exits the boat.  Is the circled part another bearing that is glassed into the hull?

We have a "sqeak" or hum when the prop shaft is spinning at certain revs (both with engine and when sailing and free spinning) that we have not been able to diagnose.

The problem started following the failure of our engine mounts.  The engine mounts have been replaced and the cutless bearing was replaced at next haul out, however a squeak has remained on our last short cruise before hauling out again.  I have checked the engine alignment, the stuffing was replaced, but the squeak remained.

We will be back on the boat again in the new year and would like to eliminate the cause for this before going back in the water and if this is a bearing then possibly order one now.

--

James
Maramu #147 (1984) <Shaft photo.pdf>


James Lochhead
 

HI,

The attached photo is of the stuffing box and where the shaft on my maramu exits the boat.  Is the circled part another bearing that is glassed into the hull?

We have a "sqeak" or hum when the prop shaft is spinning at certain revs (both with engine and when sailing and free spinning) that we have not been able to diagnose.

The problem started following the failure of our engine mounts.  The engine mounts have been replaced and the cutless bearing was replaced at next haul out, however a squeak has remained on our last short cruise before hauling out again.  I have checked the engine alignment, the stuffing was replaced, but the squeak remained.

We will be back on the boat again in the new year and would like to eliminate the cause for this before going back in the water and if this is a bearing then possibly order one now.

--

James
Maramu #147 (1984)