Advice on shaft scouring

[phorvati]

I have Aqualoy 22 shaft. It looks like PPS shaft collar was wearing against it due to engine being out of alignment badly. I had small spray back in 2020. Unfortunately I put about 500NM before getting home that year. I have since aligned the engine and pressed the bellow a bit further, further enough the stop the leak. My only suspicious observation was that I kept getting small seawater leak through the set screws on the PSS shaft collar. I would put Teflon tape on the second set screw to keep the leak from coming in.

I just hauled out to paint the bottom and took a better look.

Amazingly the set screw leak appears to be due to worn o-ring and maybe collar placed right along where shaft scouring is.
I'm trying to decide if I get a new shaft or just press the new shaft collar further in or further back to sit on fresh shaft surface.
I will definitely replace the shaft collar but I am wondering about the shaft.

Is that scouring subject to getting worse and possibly turning into a crack and breaking the shaft. Aqualoy 22 is very soft and flexible type of stainless.

[ItDepends]

That shaft is extremely beat up. Scratched, scored, and dented. The deep pitted ring is the worst, but by no means the only issue.

The chances of you getting good seals on this are very small. Just trying to push a proper fitting o-ring or lip seal over this part of the shaft will cut the rubber to hell.

[Cheechako]

That's a deep score, and corroded too............ I would replace the shaft.

[phorvati]

I am thinking about it. What hurts is the shaft is only 2 years old . After punting the new shaft 2 years ago, put new isolation mounts and moved the engine about 4 inches aft and 1/2" up in order to make servicing PSS easier. I had aligned the engine pretty good at that time.
Shaft is not bent or out of alignment because I have no vibrations any more.
With the shaft out I have already tried and slid new collar and new o-rings and have no issues.
I have two trips to Beaufort NC and back to RI with this shaft. I think the damage occurred the first year. I think engine must have settled because on the way down from RI to NC, I had no vibrations. The leak/spray happened on a way back. And i think damage occurred on that one trip, 600NM with bad vibrations. After coming back to RI (Home), I had aligned the engine again, moved the collar/compressed the bellow a bit more, and leak stopped. The only weird thing was set screw had a leak. Then I had a whole other year and another probably 1200NM with just a set screw leak that I stopped by putting teflon tape on backing screw. But i knew I had to replace the o-ring. Never imagined it would be this bad.
If shaft is structurally compromised then i will get a new one, but If not, a new collar with bellow moved a bit so that o-ring sits in front of the scoring would make the leak go away.

[ItDepends]

Originally Posted by phorvati

I had aligned the engine pretty good at that time.

How good is "pretty good"? Within 0.002 in?

Originally Posted by phorvati

...moved the engine about 4 inches aft and 1/2" up...

Wait.... Say what???

Assuming it was correct before, If you raised the engine higher than it was, your shaft is no longer straight inside your cutless bearing, which will quickly destroy it. That could be the source of your vibrations and other issues. Did you shorten the shaft when you moved the engine back?

[stormalong]

That shaft can be spray welded and machined.

Is the PSS ring's face pitted or dirty? Pictures can be deceiving. I have had mine skimmed and polished my a machinist. That was in 2009 and it is still fine.

[phorvati]

Originally Posted by ItDepends

How good is "pretty good"? Within 0.002 in?

Wait.... Say what???

Assuming it was correct before, If you raised the engine higher than it was, your shaft is no longer straight inside your cutless bearing, which will quickly destroy it. That could be the source of your vibrations and other issues. Did you shorten the shaft when you moved the engine back?

Order of events:
1. With new shaft, and new matched split coupling, new cutless installed, moved engine mounts forward(away from coupling) 4" and up 1/2" to maintain the shaft angle. did that in August 2020. Out of the water, on the stands, aligned the engine within 0.008. Filler gauge measured at 0, 90, 180, and 270 degrees. Also installed R&D Flex Coupling 910-044.
R and D MARINE : Flexible Shaft Couplings

2. Once launched, went out of alignment, Motored 6NM to the dock, lined it back to within 0.01 per R&D Flex Coupling instructions. By this time I had a good idea of good alignment vs bad.

3. In october 2020 trip to NC, 600NM no vibrations.

4. Sat in water all winter in NC.

5. Trip back in april 2021 ~ 600NM, lots of vibrations, spray/mist along the way from the shaft collar(rotor). Did not check how bad alignment got with filler gauge but did notice it. Also remember that I hit maybe a log or something under water on day 1. But at the time no noticeable damage in the engine room around the PSS shaft seal. And cant tell if that started the mist from shaft collar.

5. During summer 2021 aligned the engine and verified shaft collar had no water ingress but noticed that set screw had a leak.

6. Used the boat like that remainder of 2021 and 2022, another trip to NC and back to RI, no vibrations checked alignment along the way. Always within 0.01.

7. Last week hauled out and saw the damage.

[ItDepends]

Originally Posted by phorvati

Order of events:
moved engine mounts forward(away from coupling) 4" and up 1/2" to maintain the shaft angle.

Ahhh.... big difference between moving engine AFT and up (as initially described) and FORWARD and up...

There are a couple of things here...

First, you do not have a lightly built, flexible boat. It is possible that the shape could change enough to affect alignment when launched, but I have never actually seen that happen on a heavy cruising boat. Because it is possible, I always check. The only boat I ever had to realign after launching was a J-105.

Alignment can happen if the yard is careless about how they block the boat. This still raises a red flag that I don't understand. Especially in view of the loss of alignment while sitting at the dock without an obvious cause (loose mounting nuts?). That is just as weird. Not a very helpful observation, but it is something odd and different. SOMETHING is moving that should not be moving. Strut, sterntube, and engine stringers should not be changing their relative location. New(ish) engine mounts should not be sagging.

The set screws are not designed to be any part of the watertight sealing system. If water is leaking out of the set screws, your o-ring seal on the collar has failed. I know there are two o-rings, but the one closer to the engine is just there to maintain the alignment of the collar. The one closer to the prop is the one that is required to be leak free.

Once that primary o-ring is compromised, and you sealed the set screws, you now have a permanent pocket of totally stagnant salt water. Kind of the perfect storm for stainless corrosion. The photos of your shaft are Exhibit 1 for this effect.

O-rings on these collars are static seals. They do not (or should not!) ever move relative to the shaft--no matter what the alignment is like. The collar is clamped to the shaft. The o-rings should never fail, short of aging out of the rubber. Premature failure is almost always due to mechanical damage during installation, which is usually due to scratches, burrs or other issues with the surface of the shaft.

Sorry about the stream of consciousness writing... haven't been fully caffeinated yet this AM!

[sailormed]

Originally Posted by stormalong

That shaft can be spray welded and machined.

+1 This is the best option for a definitif solution.

[phorvati]

In the pic, that is corrosion pitting on the inside where water blocking o-ring sits. So 1+ years of stagnant, oxygen depleted water caused that. On the rim of the PSS collar that is where i believe collar made contact with the shaft and the two were colliding and that's how the gouge happened and how missing pisses of Collar rim came to be. And I think interference was so bad that oring was either gouged dented or burnt. There was a small chunk of it was missing but it was still in tack as a circle. I threw it out since. I have put new orings and slid it up and down and later inspected them for damage and could not see any damage.

I ordered a new shaft. I'll be offshore again this fall dogging November gales in New England and i don't want this on my mind.

I wonder if that one really severe gouge came from the incident where I hit something underwater while motoring.

I have that R&D flex coupling which absorbs some of the misalignment, so maybe shaft and PSS collar is dancing more that i think.

But I remember how much play there was in my cutlass bearing 2 years ago, before and after I replaced it. And I checked Saturday before pulling the shaft, and I was still very tight. No play whatsoever. So somehow new cutlass survived the entire ordeal.

I might do a repair on the old shaft this winter and keep it for the future.

[Searles]

Is there a bearing in the sterntube aft of the shaft seal ,you should not float a shaft from the stern cutless bearing to the flexible coupling to a flexible mounted engine ,ther must be a second or third bearing to hold the shaft true ,it’s almost impossible to align a motor and floating shaft plus a floating engine,.⛵️⚓️

[phorvati]

Originally Posted by Searles

Is there a bearing in the sterntube aft of the shaft seal ,you should not float a shaft from the stern cutless bearing to the flexible coupling to a flexible mounted engine ,ther must be a second or third bearing to hold the shaft true ,it’s almost impossible to align a motor and floating shaft plus a floating engine,.⛵️⚓️

Good point. My shaft is only 45". My stern cutlass is built into the hull. It does not sit on a strut. Length is very short. There was never any bearing in the middle. I remember reading something about middle support and I might be right on the margin for shaft length before another support is needed. Perhaps pressing another bearing into stern tube? This is not something that was intended by designer but I can see your point. Is all i have to do measure stern tube diameter and order another cutlass bearing for 1.5" shaft? Tap a set screw or two?

[Searles]

Yes that’s the idea, 40 dia is the normal max spacing ,we always made the front bearing 1/2 the length of the aft bearing plus kept the space from the after face of the aft bearing to the fwd face of the prop boss to 1 1/2 shaft dia ,if the engine is solidly mounted with no flex coupling you will get away with the aft cuttless only,common in commercial craft.⚓️⛵️

[phorvati]

Originally Posted by Searles

Yes that’s the idea, 40 dia is the normal max spacing ,we always made the front bearing 1/2 the length of the aft bearing plus kept the space from the after face of the aft bearing to the fwd face of the prop boss to 1 1/2 shaft dia ,if the engine is solidly mounted with no flex coupling you will get away with the aft cuttless only,common in commercial craft.⚓️⛵️

I was ready to put a cutless bearing at the PSS shaft seal end of the stern tube, but I am not so sure anymore. Engine is dancing on isolation mounts. I should not be fixing the shaft in-place at the inboard side of the stern tube. That is not far away from the transmission coupling in my case . I cannot stop the engine from moving around and if I try to fix the shaft at the stern tube something will wear out. I just have to make sure that the coupling faces are aligned and let the entire length of shaft dance around.

I remember reading this article a while back. In fact I bought custom Ace mounts in 2019 after I finally started absorbing some of this stuff.
https://www.yachtsurvey.com/Alignment2.htm

[Searles]

After reading the paper work you are relying on ,I can assure some of the assumptions made are in fact fundamentally wrong ,but it’s your boat and your money , I would check with a qualified marine engineer ,if you do away with the flexible coupling and join metal to metal you maybe fine ,if your engine mounts are all good .⛵️⚓️