Having props and shaft pulled / balanced

[Rigamarole]

We purchased a fairly large (70’) long range cruiser about a year ago. It’s lightly used - 2700 hours on the CAT C18’s over the last 15 years.

I’m looking to have a short haul done to clean the bottom and inspect the running gear. The project manager asked if I wanted to have the props and shaft pulled and balanced. It would be $5000 for that work and maybe an additional $2000 for the yard to pull the gear. There really isn’t a major vibration but at the same time, it also isn’t vibrationless at near WOT. My mind is thinking - one time after this many years might be a good idea.

Any experienced opinions on this would be appreciated.

 

[Xlantic]

If you do pull the shafts you may want to check the alignments of the shaft-support struts and the engine.

I did that during a haul-out in our boat this spring as one of the struts seemed loose.

For the alignment I used a cheap 12-gauge laser bore sighter from Amazon:

A local metalworker made a holder for the sighter from an aluminum rod with the outside diameter machined to fit snuggly in the cutless bearing supports (there are three of these per shaft in my boat: two struts and where he shaft enters the hull just by the stuffing-box). The sighter snuggly fit in a concentric hole that was made in the aluminum rod.

The target was an additional aluminum rod also machined to fit in the cutless bearing supports, with a cross to indicate the center:

The struts were aligned with shims:

A second target was machined with the shaft's diameter and fit in the transmission coupling for the shaft in order to align the engines.

At the end everything was in alignment with minimal complications and not much cost.

 

[Rigamarole]

Thanks Xlantic - that was a really helpful post. Did you have the props and shafts balanced also?

 

[Xlantic]

I checked the shafts and one was not perfect, but good enough. There are no facilities for straightening it in Menorca where the boat is based. And given the shafts are bronce and hence not too stiff It should be fine.

The boat runs very smoothly now. Since I bought it around ten years ago I would hear a rumble in the aft cabin when traveling and this is now gone.

I didn’t check the props as, again, there is no place to do that in Menorca. But at least they appear undamaged and “fair”.

 

[Dockmaster]

Why spend the money to pull and balance shafts? Unlikely that balancing does much unless you really suspect a problem there. Most vibrations are from alignment issues or excessive cutlass bearing clearances or propellers. I would have the bearings checked and an alignment performed. Neither of these requires shaft removal. The final alignment check has to be done with the boat in the water anyway.

 

[Dockmaster]

If you do pull the shafts you may want to check the alignments of the shaft-support struts and the engine.

I did that during a haul-out in our boat this spring as one of the struts seemed loose.

For the alignment I used a cheap 12-gauge laser bore sighter from Amazon:
View attachment 171277

A local metalworker made a holder for the sighter from an aluminum rod with the outside diameter machined to fit snuggly in the cutless bearing supports (there are three of these per shaft in my boat: two struts and where he shaft enters the hull just by the stuffing-box). The sighter snuggly fit in a concentric hole that was made in the aluminum rod.

The target was an additional aluminum rod also machined to fit in the cutless bearing supports, with a cross to indicate the center:

View attachment 171278

View attachment 171279

The struts were aligned with shims:
View attachment 171280

A second target was machined with the shaft's diameter and fit in the transmission coupling for the shaft in order to align the engines.

At the end everything was in alignment with minimal complications and not much cost.

Your process got everything centered it looks like. Did you do the actual alignment which is feeler gauges between the coupling flange faces? Done after being in the water at least 24 hrs?

 

[Xlantic]

No.

I understand the alignment could change when the boat is the water but my guess is that the feeler gauge approach will be inferior to the laser one given the difficulties in compensating for shaft sag and other limitations.

 

[Dockmaster]

No.

I understand the alignment could change when the boat is the water but my guess is that the feeler gauge approach will be inferior to the laser one given the difficulties in compensating for shaft sag and other limitations.

The laser method you did is for centering and not aligning. It's a great first step but is just that, a rough in centering as a starting point. Your shaft centers and trans coupling centers may be lined up but that doesn't equal an alignment. I'm glad yours is working well

 

[Xlantic]

If the the three bearing supports and the transmission coupler are all centered and aligned by the laser how can they not be aligned?

We had the laser placed in both ends and in the intervening supports.

 

[Dockmaster]

If the the three bearing supports and the transmission coupler are all centered and aligned by the laser how can they not be aligned?

We had the laser placed in both ends and in the intervening supports.

It ignores potential angular misalignment. Lots of videos and info available on this subject via a simple google search.

 

[Xlantic]

Well, I just don’t see.

We first centered the aft strut by shooting the laser from the forward bearing support. Then we aligned the aft strut by shooting the laser from there to the center of the forward bearing support.

Finally we aligned the the engine by shooting the laser from the shaft coupler in the transmission to the center of the aft strut.

(The forward strut was in alignment so there was no need to adjust it.)

So at, at the end, everything centered and aligned.

 

[Keysdisease]

Leave the shafts alone, have the props done at a good shop

$00.02

 

[firehoser75]

Xlantic,
Far from an expert here, but while I think what you did is great, Dockmaster is alluding to the fact that if the two "mating surfaces" at the coupler connection are not machined and aligned ("gapped") correctly, the whole alignment system can be "off" despite the efforts you put in. If the struts are out of alignment (meaning not trued as you did) that can be a separate issue.
That is my "understanding" and I hope this proves at least a bit helpful. Maybe someone like Steve D will give some info to clear this up?
OP: If you do pull the shafts, I suggest that you replace the cutlass bearings at the same time.

 

[Northern Spy]

If the the three bearing supports and the transmission coupler are all centered and aligned by the laser how can they not be aligned?

We had the laser placed in both ends and in the intervening supports.

What I believe dockmaster is saying is that you have ensured that the shaft is aligned relative to the cutlass, strut and center bearings. However, the laser could hit dead center of the engine side coupling when shot from the cutlass bearing and still have angular misalignment. Doing a simple face to face measurement on the disconnected coupling at 0, 90, 180 and 270 or a face to face runout with a dial indicator would verify if it is angularly aligned. Depending on the overhung load and shaft length, you may have to compensate for shaft sag with a spring scale (or a calculation). You would adjust the engine mounts to correct.

 

[SteveK]

@Northern Spy showed with pictures, specifically Angular misalignment.
Imagine the engine is sitting level, you know the shaft is at an angle from level. The feeler gauge aligns the engine to the same angle.

 

[Rigamarole]

Leave the shafts alone, have the props done at a good shop

$00.02

Thank you. I appreciate your opinion.

 

[Mac2]

Sounds like upselling. Why did he ask about balancing? Did you say anything about a vibration? As suggested I would do the feeler gauge first before taking it out.

 

[Rigamarole]

Sounds like upselling. Why did he ask about balancing? Did you say anything about a vibration? As suggested I would do the feeler gauge first before taking it out.

Yes, it probably is a bit of upselling - but I do that a lot in my business also and it’s not all bad.

The previous owner had the starboard cutlass bearing replaced by his local yard. They had an issue getting the port bearing out and it wasn’t that bad so he skipped replacing that one. So my initial service request was to do the short haul, pressure wash, and check the cutlass bearing. He said in order to check the bearing they would need to pull the props and shaft, which led to the suggestion.

In addition, I’ve read that having the prop balanced / formed or whatever they do helps with fuel consumption. And, yes, there is a vibration at higher RPM’s, which we don’t typically run at. I’m just thinking - new boat - have it done and then forget about it for the next 10 years.

 

[Comodave]

Checking engine alignment with a feeler gauge is quick and easy. It is a common problem with the engine not aligned to the shaft properly. Aligning the shaft and struts is one thing but the engine alignment is different and quite easy to be out of alignment.

 

[Xlantic]

View attachment 171295
What I believe dockmaster is saying is that you have ensured that the shaft is aligned relative to the cutlass, strut and center bearings. However, the laser could hit dead center of the engine side coupling when shot from the cutlass bearing and still have angular misalignment. Doing a simple face to face measurement on the disconnected coupling at 0, 90, 180 and 270 or a face to face runout with a dial indicator would verify if it is angularly aligned. Depending on the overhung load and shaft length, you may have to compensate for shaft sag with a spring scale (or a calculation). You would adjust the engine mounts to correct.

I agree that if the laser is only shot from one end then the shaft can end up centered but angularly misaligned. But if the laser is then reversed and shot the other way then that angular misalignment can be corrected.

In my case we used the laser approach because we had to first align the aft struts. But, having the laser and the inserts we also used them for the engine alignment. At the end the laser was centered in both directions: from the struts to the transmission coupling and from the transmission coupling to the struts. This guarantees that the shafts would end-up centered and aligned.

It is true that when the boat goes in the water the hull could change shape so a final tweak should be done to the engine alignment with feeler gauges.

But the feeler gauge alignment should be done after the shaft sag is taken into account: the weight of the overhanging shaft is estimated – using the density of the shaft material and the volume of the overhanging shaft – and half of that weight is applied as an upward force at the shaft end. From my experience at least, this is something few mechanics do.

When I have done this on my boat I needed to compensate 20 kg (44 lbs.) so I rigged a 20 litre jug full of water with a pulley system to raise the end of the shaft as it was aligned.

 

[Comodave]

I do the half weight method if the shaft isn’t connected.

 

[Dockmaster]

I agree that if the laser is only shot from one end then the shaft can end up centered but angularly misaligned. But if the laser is then reversed and shot the other way then that angular misalignment can be corrected.

In my case we used the laser approach because we had to first align the aft struts. But, having the laser and the inserts we also used them for the engine alignment. At the end the laser was centered in both directions: from the struts to the transmission coupling and from the transmission coupling to the struts. This guarantees that the shafts would end-up centered and aligned.

It is true that when the boat goes in the water the hull could change shape so a final tweak should be done to the engine alignment with feeler gauges.

But the feeler gauge alignment should be done after the shaft sag is taken into account: the weight of the overhanging shaft is estimated – using the density of the shaft material and the volume of the overhanging shaft – and half of that weight is applied as an upward force at the shaft end. From my experience at least, this is something few mechanics do.

When I have done this on my boat I needed to compensate 20 kg (44 lbs.) so I rigged a 20 litre jug full of water with a pulley system to raise the end of the shaft as it was aligned.

Just because you did the laser from both directions doesn’t mean you have it aligned. It means you have the centers touching each other. You can still have angular misalignment. In theory, if your crankshaft was removed and you shot a laser through the entire shaft line and the entire engine you could say you were aligned. But a laser from the shaft line to the rear of the engine and from rear engine back to the shaft line is not preventing potential angular misalignment. It’s your boat so if you’re happy then great, that’s all that matters. But suggesting the method you used “guarantees centered and aligned” is simply inaccurate. You may have gotten lucky and I hope you did. But I would hate for others to think this is an appropriate method to achieve alignment.

 

[Rigamarole]

Lots of really great suggestions to help me. Thanks for staying on target.

 

[Xlantic]

Just because you did the laser from both directions doesn’t mean you have it aligned. It means you have the centers touching each other. You can still have angular misalignment. In theory, if your crankshaft was removed and you shot a laser through the entire shaft line and the entire engine you could say you were aligned. But a laser from the shaft line to the rear of the engine and from rear engine back to the shaft line is not preventing potential angular misalignment. It’s your boat so if you’re happy then great, that’s all that matters. But suggesting the method you used “guarantees centered and aligned” is simply inaccurate. You may have gotten lucky and I hope you did. But I would hate for others to think this is an appropriate method to achieve alignment.

I believe the key to ensuring that everything is not only centered but also parallel is to shoot the laser first in one direction and the in the opposite one.

(Of course, this cannot be done with the shaft in place which might be the source of the confusion.)

I will try to explain what we did in some more detail.

The boat was on the hard, shaft and the Cutless bearings were removed.

The homemade laser alignment tool consisted of a cheap laser bore sight from Amazon, a machined aluminium round bar to hold the laser centered and parallel the the Cutless bearing openings, another laser holder turned to fit inside the shaft coupling in the transmission, and two targets for the laser: one for the Cutless bearing openings and the other, slightly smaller, for the shaft coupling at the transmission.

My boat has three Cutless bearings: one in the stern tube and one in each of two struts. The objetive was to align everything with the stern tube which cannot be moved or adjusted.

In our case the mid strut was aligned well enough with the stern tube so we didi not touch it. The aft struts in both engines were misaligned though.

Here is an schematic, not showing the mid strut which was fine:

The first step was to shoot the laser from the aft strut to the stern tube:

The aft strut was then shimmed in order to tilt it so the laser hit the center of the the stern tube:

The laser was then reversed and used to shoot the aft strut from the stern tube:

The aft strut was further shimmed to lower it so the laser hit it in the center:

The engine was then raised so the laser hit the center of the shaft coupling at the transmission:

The laser was then reversed to shoot from the shaft coupling at the transmission towards the aft strut:

The engine was then tilted until the laser hit the s¡center of the aft strut:

Of course, there was a lot more iteration involved but at the end everything was centered with the laser shooting in both directions guaranteeing that everythign was centered , parallel and aligned.

The process was quite straightforward and inexpensive. I can tell you, removing the starboard stern-tube Cutless bearings took a lot more time and effort than all the alignment.

 

[Xlantic]

Following from my post above:

It is standard practice to check and adjust as necessary the alignment after the boat is back in the water using the feeler gauge method. I did not do it in this case for a number of reasons:

I do not really trust the locally available mechanics to do a good job here and felt the risk of ending up with a worse alignment was quite significant.

Also i have bronce shafts which are less rigid and therefore more forgiving than SS.

Lastly, and most importantly, a few years ago I installed flexible couplings which allow some play at that end:

 

[sneal4600]

While our new to us 1987 DeFever 44OC is on the hard this winter in Michigan, we are working on the running gear. Although we did not really feel any vibrations during the last cruising season, our maintenance log showed the cutlass bearings were last replaced in 2006. No documentation on tuning the props. So after talking with the maintenance super at the yard and seeing first hand a little bit (not much) of play in the aft strut/cutlass bearing... we are replacing them. While the props are off, the were sent to Holland Prop for examination. They found a few issues with both of them that would cause wear on the new bearings and lower performance. We believe they are original Trinidad props from 1987. So all in, we are at $2500 to replace the bearings and $3000 or so to tune both props depending on the time needed for one of them which has a rather significant issue with one blade. Just sending along data points for this topic.

 

[Northern Spy]

Great write up of your methodology Xlantic! Done to a high standard. Thank you.

 

[SteveK]

The homemade laser alignment tool consisted of a cheap laser bore sight from Amazon, a machined aluminium round bar to hold the laser centered and parallel the the Cutless bearing openings, another laser holder turned to fit inside the shaft coupling in the transmission, and two targets for the laser: one for the Cutless bearing openings and the other, slightly smaller, for the shaft coupling at the transmission.

This appears to be a perfect alignment, it places the engine flange perpendicular to the shaft and should measure bang on with the feeler gauge unbolted. Then there is shaft droop out of stuffing box.
The only reason it will not be an even feeler gauge measurement all around is if the hull flexes once replaced into the water. We are told to do the coupler adjust once in the water for 24 hours. That begs the question, are the struts/shaft still in alignment.
I had not heard of shimming a strut before. Was it needed all along in the water, or was it needed because it was on the hard.
Complicated topic well reported process.
In the end if you can turn the shaft by hand, can you get it better?

 

[SteveK]

@Xlantic Please do a follow up when you do the feeler gauge checks.

 

[luna]

@Xlantic Please do a follow up when you do the feeler gauge checks.

According to post #25, no feeler gauge checks are to be done.