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Old 06-27-2020, 10:16 AM
tenders tenders is offline
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Shaft centering cones

If your boat has adjustable engine mounts, how do you know where the engine should go after a replacement or rebuild to be ideally aligned with the strut and shaft tube?

You guess. You can’t see the strut from inside the boat, and you may or may not have a clear view of the shaft tube. If you have a vee drive, as I do, you have essentially no way of seeing the shaft position in the tube without parallax, and certainly no way of maintaining the shaft’s position in that tube while adjusting the engine to it.

That’s why you need a “centering cone” sized for your shaft. A centering cone is shaped like a small solid funnel with a shaft-sized hole bored down its center axis. You first slide the shaft into the boat from the outside through the strut and Cutless bearing, but without the shaft seal, key or coupling attached. From inside the boat you slide the centering cone down the shaft, pointy end first, and tap the taper lightly into the opening of the shaft tube. This perfectly centers the shaft in the shaft tube, holding it in place and allowing you to swing the engine mounts into proper approximate position.

Once the engine is in place with the output coupling in line with the shaft, you take off the centering cone and assemble the shaft seal, key, and coupling. Then you finish the fine pitch and yaw adjustments with the nuts and threads on the engine mounts.

A boatowner would only need the one centering cone for the boat’s shaft size. A mechanic would want a set to correspond to typical shaft sizes. The market would include 100% of Moyer replacement A4 engine customers as well as anybody else who has replaced an engine of any type.
Ideal material: hard rubber, like a hockey puck. In fact this might be fabricatable out of an actual hockey puck, as that thickness would be quite usable.
Possible materials: 3D printing plastic, nylon, wood, aluminum, steel.

My prototype material: plywood. See photo #1. I sanded the taper with the wood spinning in my drill press since I don’t have a lathe. It’s extremely crude...but it’s actually very useful. From this I learned that my engine has likely been 3/8” offset from my shaft’s natural position for the last 25 years. See photo #2.

Possible design improvements:
* fabricate them in halves that get zip-tied or otherwise strapped around the shaft so the coupling need not be removed to get the cone on and off the shaft.
* fabricate them in a slightly flexible material with a cutout, making them “C”-shaped, so they snap around the shaft and hold themselves in place, again avoiding the need to remove the coupling to install and uninstall the cone
* use a gradual taper (ie, a taller cone) to hold the cone more firmly into the tube - at some risk of increasing the size of the cone beyond what will fit in some installations
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Old 06-27-2020, 11:54 AM
Hawkeye54 Hawkeye54 is offline
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Smile Shaft centering cone -

Really a brilliant, yet simple solution ! I like it

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Old 12-26-2020, 02:35 PM
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Elizabeth_B29 Elizabeth_B29 is offline
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Centering “ Cylinder” for shaft alignment

I have what I call a centering cylinder.
I was fortunate to be restoring my Bristol 29 next to a machinist Who was also restoring a similar sailboat.
He saw the frustration I was having trying to get my shaft aligned.
I struggled with it for days sitting behind it moving it incrementally measuring, shims blah blah blah. Think I was cussing a bit too much .
He arrived one day with a 2.5” long cylinder of Delrin, drilled with a 7/8 ish inch bore. The outside diameter fit into the Shaft log and the inside diameter was drilled to slip onto the shaft, both almost snugly.
It’s a wonderful thing to have when you realign your shaft. The cylinder slides into the shaft log the shaft slides through “the alignment cylinder” and up to the coupler. This with the stuffing box and hose portion removed.
In my case I was adding a drive saver ( rubber donut ) so a portion of my shaft was cut off and re-keyed before all was said and done.
Using this tool made it much easier to get really closely aligned. I then just slid the shaft back towards the stern enough to clamp on the stuffing box/hose assembly and then I slid the shaft back to the coupler and snugged it up in the coupler.

My engine was thrown all out of whack initially when I found my boat had been moved to the dry storage area after I had un bolted my engine and gone on vacation after struggling and giving up temporarily. When I came back my boat was nowhere to be found in the work area and my engine was literally off the mount rails, a bumpy ride on the Travel lift. Lots of alignment torture ahead... the tool made it much easier.

So, that piece of plastic worked wonders annnd I vowed that I would wear is a piece of jewelry so wouldn’t lose it, ha ha. Now I don’t know where the heck it is, it is in some bin of parts And I’m going to have to go look for it.

Someone should manufacture these things (on a fine silver chain to wear ) and sell them.


Last edited by Elizabeth_B29; 12-27-2020 at 01:03 PM. Reason: Move to wish list
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Old 12-27-2020, 08:47 AM
W2ET W2ET is online now
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How many thousandths beyond the nominal diameter would you open up the hole to ensure an easy sliding fit?

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Old 12-27-2020, 12:48 PM
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Elizabeth_B29 Elizabeth_B29 is offline
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Shaft Centering Tool - specs

Hi Bill,

I’m not quite sure but I’m going to try to find it and I’ll mic it and get ID and OD measurements.

The one thing to remember is that alignment was done after a brand new Cutlass bearing was installed first, so there was no shaft slop at the Cutlass bearing.
I also checked prop on and prop off as I was curious how this weight might affect the alignment. In my case it did not appear to make a difference.

I used a new shaft that was intended for a C&C that had to be cut.
After my shaft was cut and re-keyed to a shorter length to accommodate the new Drive saver, I did find a Small burr On the edge of the keyway that could have scratched the alignment tool.

So it probably would be good check with a soft cloth before you slide your shaft into the centering tool and make sure there’s no burrs or anything outstanding that would cause damage to the tool. Delrin is pretty hard but I think it could be gouged by a sharp burr.

In my case I just took strips of crocus cloth and polished out the burr.

So maybe some industrious individual could machine these for us, as we all know engine alignment is a “ booger bear”


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Old 12-27-2020, 08:43 PM
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ndutton ndutton is offline
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It's encouraging to see that members here understand the importance of centering the shaft in the shaft log as part of a proper engine alignment. I doubt it would happen on any other sailboat forum on the internet, certainly not the ones I've had the misfortune of stumbling across.

Kudos to Elizabeth and Ted, well done.
1977 Catalina 30
San Pedro, California
prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others
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Old 12-28-2020, 01:06 PM
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Elizabeth_B29 Elizabeth_B29 is offline
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Thanks All!!!

I’ll find it and get some pictures out to you and some specs
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Old 12-31-2020, 07:40 AM
Indy Indy is offline
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Originally Posted by Elizabeth_B29 View Post
I’ll find it and get some pictures out to you and some specs
I'd love to see the pics posted here. I can't read a description alone and really get a handle on how something works. This is awesome; thank you both for sharing your ideas.
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