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Old 17-02-2024, 08:25   #1
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Acceptable prop shaft wear?

I'm helping a friend with her 1984 Catalina 30. The motor is getting rebuilt, the keel stub repaired, and other boat fun.

The boat is used by the local school, so we'd like to avoid headaches and needing service during the (short) summer season.

The prop shaft is 1.000", except at the stuffing box, where it's worn to .980" diameter. The owner is running out of boat bucks. Are we likely to get 5 years service from this shaft, or should we replace (maybe just shorten?) the shaft while we have the motor out?

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Old 17-02-2024, 08:58   #2
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Re: Acceptable prop shaft wear?

I am doubtful you will get 5 years out of that and whilst the traditional stuffing boxes will tolerate some wear, they will drip not only in use as they should, but also likely when stationary, or under sail if the prop turn the shaft.

Recently had to replace a 1" shaft which cost me £250 because I like the dripless Volvo seal. Sadly damage by a professional marine engineer meant despite polishing it with emery paper to 1200 grit and achieving a really smooth shiney surface there was something not right and it dripped constantly.

If you can take it out and alter the length to a clean unused section for the stuffing box, you might get a season or two out of it.

I value dry bilges more that the cost of a new shaft, since wet bilges create damp and smells.
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Old 17-02-2024, 10:01   #3
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Re: Acceptable prop shaft wear?

you would need to do the coupler along with the shaft. it's not really cheap and best left to professionals. if you keep it in place make sure the shaft has no play in the coupler.
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Old 17-02-2024, 10:21   #4
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Re: Acceptable prop shaft wear?

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Originally Posted by gonesail View Post
you would need to do the coupler along with the shaft. it's not really cheap and best left to professionals. if you keep it in place make sure the shaft has no play in the coupler.
Agreed!

Thankfully, the biggest prop/shaft shop in the area is not too far up the road from me.

I'm just trying to figure out the risk/return. As she sits now, the motor is out and the coupler is off the shaft. If we need to play with it, now it the time. If we can get maybe another 1000 hours out of it, we can leave it until the next major service.
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Old 17-02-2024, 11:19   #5
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Re: Acceptable prop shaft wear?

The wear at your stuffing box area is of zero importance. The reason for this is because a stuffing box, by design, compresses the stuffing between the box and the shaft. When the stuffing box nut is tightened it is compressing the stuffing against the shaft and it will do this just as efficiently whether the shaft iis 1.000 or .980. It literally makes no difference. So, if it is adjusted correctly it will NOT leak when the engine is not running.

Keep the shaft. It's fine.
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Old 17-02-2024, 11:29   #6
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Re: Acceptable prop shaft wear?

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The wear at your stuffing box area is of zero importance. The reason for this is because a stuffing box, by design, compresses the stuffing between the box and the shaft. When the stuffing box nut is tightened it is compressing the stuffing against the shaft and it will do this just as efficiently whether the shaft iis 1.000 or .980. It literally makes no difference. So, if it is adjusted correctly it will NOT leak when the engine is not running.

Keep the shaft. It's fine.
This is true. As long as the surface in way of the packing is smooth and the rest of the shaft is in good condition I would not worry.
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Old 17-02-2024, 11:36   #7
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Re: Acceptable prop shaft wear?

another possibility is to add weld material in the worn spot and remachine to standard size. Should be considerably less expensive than a new shaft.

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Old 17-02-2024, 12:15   #8
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Re: Acceptable prop shaft wear?

I think you should at the very least use some boat bucks the make sure the engine is properly aligned, probably requiring new mounts or mount work. Thats why the shaft is wearing,luckily it's a low rpm low hp engine so I wouldn't worry about it breaking if you are just day sailing.

Assume the cutlass bearing is worn funny as well. Engine alignment is key.
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Old 17-02-2024, 12:48   #9
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Re: Acceptable prop shaft wear?

How old is the current shaft? You've had 2% wear in whatever that time frame is.

As a seat of the pants, I'd be comfortable with 5% wear before replacing on that shaft. So do the math as to how much longer you have...

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Old 17-02-2024, 12:48   #10
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Re: Acceptable prop shaft wear?

I agree with PaulS - old-style packing glands don't really care what diameter the shaft is, as long as it's smooth and round. I'd run that shaft for years without a second thought. (assuming the pic the shaft is pulled forward, the shiny band near the coupling is what rides in the packing.)
Note: Wear like that may be due to grit in the packing (muddy water, powering off a sandbar, etc.) and/or packing adjusted too tight. For sure clean out the replace the packing in the gland while you've got easy access.
The shiny spots further down the shaft are indicative of alignment being off (or engine mounts too soft), causing the shaft to contact the shaft log behind the packing. Lots of folks think alignment is all getting the coupling faces parallel, but the first step is "macro" engine positioning to get the shaft centered in the log (ideally when the boat is in the water), then check it again after adjustments to align the coupling faces.
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Old 17-02-2024, 13:17   #11
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Re: Acceptable prop shaft wear?

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Originally Posted by Bellinghamster View Post
I agree with PaulS - old-style packing glands don't really care what diameter the shaft is, as long as it's smooth and round. I'd run that shaft for years without a second thought. (assuming the pic the shaft is pulled forward, the shiny band near the coupling is what rides in the packing.)
Note: Wear like that may be due to grit in the packing (muddy water, powering off a sandbar, etc.) and/or packing adjusted too tight. For sure clean out the replace the packing in the gland while you've got easy access.
The shiny spots further down the shaft are indicative of alignment being off (or engine mounts too soft), causing the shaft to contact the shaft log behind the packing. Lots of folks think alignment is all getting the coupling faces parallel, but the first step is "macro" engine positioning to get the shaft centered in the log (ideally when the boat is in the water), then check it again after adjustments to align the coupling faces.
I am all in with the wear doesn’t matter to the packing gland. That much wear comes from either tightening the packing too much (it should drip just a little when turning), or from operating in waters that have a lot of suspended abrasive sand or silt.

It’s not unusual that packing that is old, dried out, and past it’s “best by” date stays in service. To stop the drip that then happens when the shaft is still, the shaft gets over tightened, and wear begins.

Take any money you might have imagined spending on a new shaft and replace the engine mounts, and have the engine carefully aligned by someone who know what they are doing. You have already heard that from others…
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Old 17-02-2024, 14:36   #12
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Re: Acceptable prop shaft wear?

Excellent!

I'll not worry about the shaft.

New motor mounts have been ordered. The cutlass bearing is new(ish) and seems OK.

The engine alignment was significantly bad when I pulled the motor. Yes, the shaft is pulled forward in the pic, and that explains the shiny spots on the shaft- thanks!

In general, this boat has not had preventative maintenance. I'm sure that the packing was tightened until the "leak" stopped.

Another question-

I was planning to remove and replace the hose for the packing gland. I can't get it off the spigot in the hull with any reasonable means. I'm tempted to leave it. I was planning to center the prop shaft in the spigot to start the engine alignment. How can I make sure the shaft is in the correct place before I start the motor alignment?

I'm planning to align it as well as I can on the hard. A few days after launch, I'll have someone with actual skills do the final alignment.
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Old 17-02-2024, 17:09   #13
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Re: Acceptable prop shaft wear?

I just ordered a new 1” shaft for a friend all in with coupler, fit and faced, nuts keys the works was $580 shipping included. Other option would be to add a PSS approx $300 as the bellows will bridge the wear spot.
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Old 17-02-2024, 17:20   #14
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Re: Acceptable prop shaft wear?

What I've done before is to cut a very thin slice off the arse end of the cutlass bearing, if you can get to it, after pulling the shaft....plus/minus 1/16-1/8", re-insert the shaft, and insert over the the shaft at the front end of the prop tube.
This way you'll know that shaft is centered in the tube and can align the engine flange and prop flange so that it is spot on.
After which, you remove the that sliver of cutlass bearing and replace the stuffing box, etc.
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Old 17-02-2024, 20:59   #15
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Re: Acceptable prop shaft wear?

I did a C30 last year, and the new shaft was $600, including facing the coupler and lapping the prop. The shaft came in 2 days from a local machine shop because Catalina Direct had a two week lead time. The boat was also in a school program so time was of the essence.
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