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Old 09-21-2018, 01:51 PM   #21
City: Princeton Jct
Join Date: Feb 2014
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Prop Shaft Support

The maximum recommended unsupported distance for a 1.75" shaft is approximately 72". Yes, you will have significant shaft whip if you have an unsupported length of 130". Since this is not underwater, I might suggest fabricating a shelf and installing an intermediate greasable bearing at the mid point.
Best Regards, Blair Bugher

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Old 09-27-2018, 02:02 PM   #22
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Vessel Name: Waves of Grace
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Alright, thanks everyone for the input. We have spent a bit of time running the boat at various speeds and observing the shaft. When running at lower speeds, we do occasionally (but not all the time) get a bit of whip in the shaft observable at the PSS shaft seal - the recommendation from my mechanic and the shaft supplier is to install a pillow block just ahead of the PSS. That will reduce the unsupported shaft length to within recommendations.

I'll post my progress but it won't be until December at the earliest!

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Old 05-11-2019, 09:15 AM   #23
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Here is what we ended up doing. A Royersford split journal bearing was purchased from the shaft supplier and installed about 6" forward of the dripless shaft seal. This was accomplished by glassing pads onto the stringers and then fabricating a metal support structure that was then powder coated and installed. Our shaft and prop (which are both only a year old) were pulled and checked, then the whole thing was reassembled.

We now have a very smooth running shaft and I can say it is definitely an improvement.

The split journal bearing has a grease nipple on top of it that needs to be attended to occasionally. In my install, once things were closed back up, the journal bearing sits about 18" forward of the access hatch. For ease of greasing, I installed a 24" grease whip and permanently installed a grease gun to the side of the access hatch. Now all I have to do is reach in and give it a pump every once in a while.

Quick side note - I am observing the journal bearing temperatures with a temp gun. Initially I was concerned about the bearing running a bit hot. A quick phone call to my shaft supplier and they told me that these bearings will run warm until it settles in, or if over greased. Looks like they were correct, as the temperatures are settling substantially.

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Old 05-11-2019, 10:37 AM   #24
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Some consideration could be applied to the PSS.

These shaft seals allow about 1/4” runout w very little resistance. If a prop shaft is prone to whip some the PSS probably won’t control it at all or only to an extremely small degree.

A stuffingbox on the other hand typically has a stiff hose supporting the packing gland and the shaft. The hose type/design, stiffness and length will vary the amount of shaft support but it will be many times as much support as the PSS.

But there’s a strong possibility better support for the shaft would result if a stuffing box type seal was employed. And IMO water would provide lubrication enough for fairly long lived packing life. Also boaters tend to think the closer to no leaking is best and run the packing too tight. Kinda like a car burning no oil. But as long as the amount of water leaking in is not a problem I’d be wanting considerable leaking .. within reason.
Also maybe I’m an idealist but I reason the there is a reason a prop shaft whips. Alignment and balance should stop whipping but controlling it with bearings is probably never a 100% solution. So IMO one should check balance and alignment first before adding bearings.

North Western Washington State USA
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Old 05-23-2019, 04:26 PM   #25
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Installing an additional bearing ahead of a dripless packing will further complicate matters when you need to do any repairs to the dripless.
This will only happen on rough crossings in the middle of the night, and is a blatant violation of the KISS code.
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But you can't make him ski...
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Old 05-24-2019, 09:13 PM   #26
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prop shaft support

Originally Posted by hobbystuff View Post
I am looking for some information regarding the shaft setup in my Universal 36 Tri-Cabin.

Currently I have a 1.75" Aquamet 22 shaft, driven by a 120 Lehman, the shaft was installed last year prior to the season, the new shaft was installed exactly as the old one.

There is one cutlass bearing at the stern tube (which was also just replaced), the overall shaft length from stern tube to transmission flange is 130 inches. The shaft exits the tube at a cross-member that is ~ 60" back from the transmission coupling. A PSS shaft seal is mounted at that location. During discussion with the shaft supplier, he mentioned that this is a fairly long unsupported length, but that at our engine rating/rpm it "should" work out fine. My mechanic at the time convinced me of the same.

The boat has run just fine, although I feel like it could run smoother. Occasionally I think the shaft may experience a bit of "whip" at certain, low RPM settings.

This winter I am pulling the boat for several months so that I can do a rebuild on the Lehman. I am using a new mechanic, and during discussions he suggested we may want to take the time to install a cutlass bearing at the PSS seal to provide some additional shaft support. I have some questions:

(1) I have no idea what the original stuffing box arrangement looked like on this boat, since the PSS was installed before I acquired it. Where the shaft exits the cross-member, there is a brass tube with a bolted flange that looks as if the threads were turned down to allow the PSS to slide on. While there is considerable clearance for the shaft in the shaft tube itself, this brass tube narrows the exit to about ~1/4" clearance around the shaft. This leads me to believe that in the original configuration, the stuffing box was located at this point and provided some additional shaft support.

(2) I am considering fabricating a new component that would allow me to install a cutlass bearing at this location, which would reduce the unsupported shaft length from 130" to 60" (transmission to PSS), and 70" (PSS to Shaft Log). My new mechanic seems to think this would be a nice improvement.

Long winded, I know. Any thoughts on this? What I don't want to do is go to all the work, and then find out I just made things worse.....

Thanks in advance.
Here are a few pics of how my P.O. addressed possible shaft wobble. That bearing is bolted to a rubber block glued into the bilge directly above the keel.
Hope you have found a remedy by now if not something for your consideration.
Attached Thumbnails
DSC03486 (Small).JPG   DSC03487 (Small).JPG   DSC03489 (Small).JPG  

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