Mismatch between stern tube OD and prop shaft/standard stuffing box size - SailNet Community

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Old 12-16-2011
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Mismatch between stern tube OD and prop shaft/standard stuffing box size

It appears that Pearson built the 28-1 with what is now a mismatch: a 1 ½” diameter smooth fiberglass stern tube and a 7/8” propeller shaft. The standard stuffing box size tube for a 7/8” propeller shaft now has an ID of 1 ¾”, not an ID of 1 ½”, which is now the standard size for a ¾” propeller shaft. Photo link: SailNet Community - jameswilson29's Album: Winter repairs: replace stuffing box hose - Picture

Here are my options, as I see it:

1. Buy stuffing box for ¾” shaft and re-bore to 7/8” size (problem: will probably never pack right and will weep excessively or overheat);

2. Epoxy prefab fiberglass tube with 1 ¾” OD and 1 ½” ID to existing stern tube to increase diameter;

3. Lay additional fiberglass to existing stern tube to increase diameter;

4. Buy and install ¾” propeller shaft and alter all lower end parts (too expensive); or

5. Clean and wrap existing stern tube with silicone tape to add ¼' to diameter and/or coat with 3M 5200 sealant before applying hose to tube for better seal (problem: not structurally sound and creates difficulty with next removal of tube?).

Any other ideas? What is the best way to rectify the mismatch?

Last edited by jameswilson29; 12-16-2011 at 11:13 AM.
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Old 12-16-2011
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Why do you need a new packing gland? Normally these things will out last the boat and all that needs replacing is the hose.
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Old 12-16-2011
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Why change the box: it's made of brass ,just clean it up, Replace the hose & repack it. This lasted how long? It's tested, If its not broke don't fix it!-Dale
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Old 12-16-2011
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Maybe my approach was mistaken. The packing gland was quite corroded and appeared somewhat stripped (photo: SailNet Community - jameswilson29's Album: Winter repairs: replace stuffing box hose - Picture ). Since I was replacing the hose and the propeller, I thought it was a good idea to replace the entire packing gland (and the cutlass bearing) while I was doing the work.

The stuffing box was leaking excessively. From the work I have done so far, it appears that there was not sufficient room to re-pack it without removing it from the propeller shaft, probably due to the drivesaver added to the coupling and the length of the original coupling (I hope the new shorty coupling will cure that problem). I doubt it was properly serviced in the 15 years since the boat was repowered with an inboard diesel in place of the A4. I will take a photo of the old flax packing when I remove it.

Last edited by jameswilson29; 12-16-2011 at 11:39 AM.
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Old 12-16-2011
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Quote:
Originally Posted by jameswilson29 View Post
It appears that Pearson built the 28-1 with what is now a mismatch: a 1 ½” diameter smooth fiberglass stern tube and a 7/8” propeller shaft. The standard stuffing box size tube for a 7/8” propeller shaft now has an ID of 1 ¾”, not an ID of 1 ½”, which is now the standard size for a ¾” propeller shaft. Photo link: SailNet Community - jameswilson29's Album: Winter repairs: replace stuffing box hose - Picture

Here are my options, as I see it:

1. Buy stuffing box for ¾” shaft and re-bore to 7/8” size (problem: will probably never pack right and will weep excessively or overheat);

2. Epoxy prefab fiberglass tube with 1 ¾” OD and 1 ½” ID to existing stern tube to increase diameter;

3. Lay additional fiberglass to existing stern tube to increase diameter;

4. Buy and install ¾” propeller shaft and alter all lower end parts (too expensive); or

5. Clean and wrap existing stern tube with silicone tape to add ¼' to diameter and/or coat with 3M 5200 sealant before applying hose to tube for better seal (problem: not structurally sound and creates difficulty with next removal of tube?).

Any other ideas? What is the best way to rectify the mismatch?
Not sure about the concern of the ID specs as long as the OD"s are close enough for the hose to accommodate? also, maybe it is just the photo but it looks like the engine may be mounted way too low? Is the cutlass bearing wearing evenly front to back? If uneven shaft alignment may be off? Were there any problems with the existing setup?

Dabnis
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Old 12-16-2011
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There were no problems with the existing setup, except that the stuffing box hose was cracked, and replacement was recommended by the surveyor.

The engine ran great, although less vibration would be preferable.

The stuffing box was leaking too much, probably 15-20 drops a minute.

I have only owned the boat for 2 months so I did not check alignment; I have been more concerned with the surveyor's recommendations.

Last edited by jameswilson29; 12-16-2011 at 11:45 AM.
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Old 12-16-2011
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Wrap with fiber glass is the best way to increase the diameter. Pss makes a dripless packing that will fit 1 1/4" up to a 2/14" stren tube for a 7/8" shaft. dripless is the only way to go
PSS Small Shaft Seals | PSS Shaft Seal
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Old 12-16-2011
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Thanks for all your responses, and thanks particularly for the new option of a dripless seal - that will be my solution to the problem.

(It also solves another P28 potential problem - galvanic action on the keel-stepped mast from salt water in the bilge.)
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Old 12-16-2011
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The box could be bad but it sure looks like just a bit of normal green stuff and should clean up like brand new ?
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Old 12-16-2011
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The box could be bad but it sure looks like just a bit of normal green stuff and should clean up like brand new ?
Ditto! I've yet to see one my bench grinder and brass wire wheel could not make look like brand new in about 5-10 minutes..
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