How To Align Prop Shaft After Months On Land

[benethridge]

Hi, everyone.

My Vagabond 42 has been hauled out for many months now. I recently bought a new prop shaft and when I tried to align it to the transmission coupling, I noticed that it is about 1/2 inch too high. When I took the prop shaft off many months ago, it was perfectly aligned...or at least it came off easily. Now I can't even bend it into place (probably not a good idea anyway).

The boat rests on blocks on the keel, with jack stands as well, of course.

I'm thinking that this misalignment is due to the forward and aft ends of the fiberglass hull flexing downward over time, due to gravity. I have read that you should never try to align the prop shaft to the transmission out of the water, due to this flexing.

Do you think this is the problem? If so, how long does it need to be in the water before it will come back to its normal shape? Days? Weeks? Months?

Ben Ethridge

[CarlF]

It should bend back the moment the hull is supported by water. If not, you have another problem.

There’s a good chance your shaft was out of alignment before. It could be out of alignment and still be easy to remove. One possibility is that the engine mounts are old. If they are over 10 years old, consider replacing them.

Is the cutlass bearing in good shape?

In most cases, iwhen replacing a shaft you should buy a new coupling. Couplings are cheap. You should also have the shaft and coupling fitted by a shop that knows what it’s doing https://pbase.com/mainecruising/new_shaft

[chris95040]

Maybe I’ve been blessed with unusually stable hulls the past 20 years, but I’d never in a million years have guessed 0.5” out of whack would be possible even after an extended stay on land.

I think you should take a much closer look at everything.

Is your stuffing box attached directly to the stern tube or with a flexible hose? If firmly, is the packing removed from your stuffing box? Use spacers in there instead of packing while aligning on land to prevent it’s mostly arbitrary geometry from messing with you.

Did a flexible engine mount fail? Did your engine bed sink due to a structural problem?

How long is your shaft, and where along that length are the major components?

If you rotate the shaft, does it remain 0.5” high, or does it wobble around?

My 40 foot yawl was on land for 3 years (long story). Her prop shaft was disconnected to replace a transmission about 1 year into that. 2 years later, when I finally put her back together, the couplings mated right into each other, no help from me other than pushing from the stern. I think the caution about aligning on land is to catch a few extra thou of coupling fit, not something as extreme as 0.5” out of whack! If your hull is that flexible I’d be worrying about my shaft breaking every time I motored in heavy seas.

[MicHughV]

the secret is this.....that shaft must be perfectly lined up inside the shaft log....ie, the tube that goes thru' the boat....if it is not perfectly lined up, the shaft will wear unevenly...

ok, step 1....remove the hose and packing gland...and the shaft flange....
step 2..you can visually check this....but if you have an old cutlass bearing, cut about 1/4-1/2" off and slide this over the shaft and back into the tube, just the front edge, as you have to remove this when done, so leave something for a big wrench to fit around.......this will align the shaft properly inside the shaft log..you can use a ruler to go around the shaft to check clearance between the shaft and shaft tube...but having a piece of old cutlass bearing makes the job easier..
step 3.....re-attach the flange....and now slide the shaft, with flange attached, close to the engine flange...and check for alignment....you should be able to quickly tell if you have a problem...
step 4...adjust the engine to suit the prop flange....this may take some doing....as all the engine mounts must be loosened...
step 5....once the engine flange aligns properly with the prop flange, properly means
no more than about .005" gap anywhere......remove the prop flange, remove that little section of cutlass bearing you inserted earlier and re-attach the packing gland.....
step 6, do a final flange to flange gap check and adjust accordingly.
step 7...re-attach all the flange bolts and shaft retainer bolt, making sure you use wire or some other method to prevent them from vibrating loose...use the wire only after you have checked the alignment again, once it's in the water..

I can't see how or where this 1/2" gap materialized...the Vagabond 42 is a pretty sturdy boat...if you have a 1/2" gap, you might have a problem elsewhere...

[Q Xopa]

Originally Posted by benethridge

Hi, everyone.

My Vagabond 42 has been hauled out for many months now. I recently bought a new prop shaft and when I tried to align it to the transmission coupling, I noticed that it is about 1/2 inch too high. When I took the prop shaft off many months ago, it was perfectly aligned...or at least it came off easily. Now I can't even bend it into place (probably not a good idea anyway).

The boat rests on blocks on the keel, with jack stands as well, of course.

I'm thinking that this misalignment is due to the forward and aft ends of the fiberglass hull flexing downward over time, due to gravity. I have read that you should never try to align the prop shaft to the transmission out of the water, due to this flexing.

Do you think this is the problem? If so, how long does it need to be in the water before it will come back to its normal shape? Days? Weeks? Months?

Ben Ethridge

Yes highly possibe.

When out of the water the boat is sitting on the keel pushing it and the engine bed up.

When in the water the keel is hanging down.

Its also possible the alignment wasnt perfect before.

[lvictorlucas]

I would suggest letting the boat sit in the water at least over night before starting to align the shaft and then recheck it after several weeks or a month.

[benethridge]

Good thoughts/questions, all.

The engine mounts are new. We re-aligned in the water before we hauled out, so I know it was aligned at that point.

The cutlass bearing is fairly new, but I see your point about installing a new one.

The shaft is about 6-7' long. I'm not at the boat for another month, to measure things precisely yet.

Good article from Maine Sail. Thanks. General Propeller built the new prop shaft from stock, and they appear to have done an excellent job, so I'm pretty sure the shaft is not out of round. The new prop shaft coupling fits on it perfectly.

I removed all the packing material in the stuffing box, so yes, that could be the culprit. Let's see how it looks after installing the new material.

I'll call General Propeller next and ask them what they think it might be, given all your suggestions above.

Thanks for the advice.

Ben

[Compass790]

Ben there are you tube vids on alignment as well is you prefer audio visual instructions rather than written.

[flyingfin]

Probably best to re-bed the bolts holding the strut to the hull and remove/replace the cutlass if the vessel is more than 10 years old,,,,,,,,,nothing lasts forever. Then splash her and let sit for 48 hours before trying to adjust motor mounts/align shaft. Hull may be warped or just supported in an odd way that is creating the mis-alignment. Or your old shaft may have been slightly bent!

[mjgill1]

Put her in the water. Let her hips settle out for a week then see where you are at.

[jkishel]

Perhaps when she was hauled the aft sling was misplaced and bent the strut (and maybe the old shaft as well). If the sling was on the shaft forward of the strut it could have bent the strut up. That would bring a perfectly straight shaft high to the output flange.

[MicHughV]

why was the old shaft replaced ???
just curious .....
I've been thru' some of these trial and tribulations myself....where the flanges met up, but the shaft was not inline inside the shaft log...this caused the shaft to wear unevenly at the rear cutlass bearing....so much so, you could plainly see the wear marks on the shaft. Hard to believe rubber can wear out stainless steel....but it did...

which is why, I think it's important to make sure the shaft is centered inside the shaft log before trying to match up the shaft flange to the engine flange.

I simply don't see the 1/2" misalignment as hull sagging...that's a lot....that would cause a crack somewhere.....there must be another reason......an imperfect haulout as described above happens a lot...so would definitely start there...

regardless, center the shaft inside the shaft log first....then match flanges....once in the water check again....

[Knotical]

Was standing rigging loosened/removed after haul out? That would change the shape of the hull.

[George DuBose]

I have a 1973 Pearson 36. Between the propeller shaft and the transmission flanges there is a flexible coupling about 2" thick. My local mechanic says he can't align the flanges with the flexible coupling in place and I can't bring the two flanges close together due to the Flex-o-fold prop being 1/4" away from the P strut.

The only way to get the flanges together is if the prop is off and the boat is out of the water. Meaning any prop shaft/tranny alignment has to be done out of the water.

Unless some genius on this blog has a solution...please...

[jeepers]

Originally Posted by George DuBose

My local mechanic says he can't align the flanges with the flexible coupling in place and I can't bring the two flanges close together due to the Flex-o-fold prop being 1/4" away from the P strut.

The only way to get the flanges together is if the prop is off and the boat is out of the water. Meaning any prop shaft/tranny alignment has to be done out of the water.

Would be a 2 step operation.
1. You have to project the center of the prop shaft to the center of the transmission output shaft. Both should have centering V's machined in the end face of the respective shafts.
You can do this by using a machinists square/straight edge & a digital caliper.
Put the straight edge on a length of the prop shaft that is the same uniform machined diameter.
Measure from centering V to straight edge Then project this to the center point "V" of the Transmission output shaft.
Do this top & bottom & both sides = 4 ways on the prop shaft & project to transmission shaft center.
When after adjusting the engine & transmission where necessary.
This only aligns the centers of the shafts.
Next step. To align the center of rotation of both shafts
2. You still have to have a flange on the transmission & a flange on the PROP SHAFT. Hopefully of the same outside diameter. But it isn't totally necessary, as long as your consistant.
By using the caliper you can now measure between the flanges at the top face, bottom face & both sides.
When these measurements are equal the shafts are directly in line.
NB. You will probably have to do it several times since any adjustments affecting the engine transmission in Step 2 will affect the transmission out put shaft center to prop shaft center from Step 1. Only because of the cantillever effect of the distance of the flange on the transmission to the engine & transmission mounts. But all in all. Much easier than rebuilding & synchronizing 4 carburetors on a 4 cylinder engine.
I think I would be inclined to shim the bottom of the transmission flange to bed of the boat that secures the engine & transmision. With pieces of steel tubing, flats etc.(notwood)