A25 Stern Tube Replacement

[Armatore]

Hi All;
My first time to post here.

I have an A25 Deluxe from 1977. Have had lots of adventures but now I am looking at replacing the stern tube with a fiberglass tube and a full size cutless bearing. I'm wondering if anyone has done this and can tell me if the original bronze tube is just stuck into the hull and glassed on each end, or is it bedded in something for the whole length? I think I remember that when I was working on the motor mounts and installing a thrust plate for a Python Drive there was some sort of a rock hard filling compound under the glass at the rear of the engine support stringers that was a real bear to remove. I hope that during original construction and before the floor pan was installed in the aft cabin, they didn't pour the keel full of this stuff after installing the shaft tube! Any help from someone who has info. about original construction of the shaft tube would be greatly appreciated.

Thanks.

Mark Rondel
A25 "Pollywog"
Harbor Springs, MI

[dkirsop]

Here is a drawing depicting the shaft, shaft log and seals. It appears that the shaft log extends as a single unit from the cutless bearing to the shaft seal in the boat. Sorry for the delayed posting but there was a problem with the drawing file.

Shaft Log.png

[Armatore]

Wow, thanks so much for the drawing. It looks exactly like what I can see of my tube. Unfortunately it doesn't shed any light on the question of what happens to the tube inside the skeg. I don't know if it is free floating or if it is encased in some kind of filler. If I can just cut it free at the fitting at the aft end and the bulkhead forward by the engine compartment that would be easy. If I have to drill out the "deadwood" to accommodate my new shaft tube that is a different story. My new shaft is 1.25" and the tube is going to end up almost 2" diameter. I believe that is slightly larger than the original tube. Thanks much for the drawing though.

[dkirsop]

If you want to do a little "digging" this site is a comprehensive collection of Albin drawings and documents

https://digitaltmuseum.se/search/?q=Alb ... tdesign%22

[Dieselram94]

Hold on here… are you referring to the dark colored substance in the keel? I’m color blind mostly but it’s either pink, blue, purple or possibly a gray? I’ve found this odd substance in the center of my keel, almost like the two halves of the keel are bonded together with it? Anyways, I can confirm the tube is a single piece. I also can tell you it is 100% possible to install a 1.25” shaft into it. Does not require a new stern tube to run the bigger shaft. That’s the size my A 25 is running. Very easy to install.if interested I can provide more details on how to acccomplish the swap.

[Armatore]

Thanks Dieselram94, I have already replaced my shaft in the existing tube with a new 1.25" shaft. Problem is I still have a vibration I'm not happy with. I fabricated a new cutless bearing to fit the original stern fitting and after a couple of years of minimal use I see more wear than I'd like. I want to use a full length (5") 1.25 cutless bearing so I've fabricated a new tube to replace the original that incorporates the new longer cutless bearing. What I am worrying about is whether the keel area under the cabin sole in the aft cabin was filled with the dark colored substance you mentioned (I think mine was gray) around the original shaft tube. I seem to remember that the "dark colored substance" was very hard, like high density concrete. I think I dulled drill bits trying to drill through it, and had a hard time grinding it with a side grinder. If this is the case it will be very difficult to drill an oversize hole to accommodate my new shaft tube which is ending up about 2.25" O.D. I was hoping someone has worked under the cabin sole and could enlighten me as to what I will find under there. Thanks for your help

[DesertAlbin736]

Thanks Dave, will add to my collection of Albin drawings for future reference (and to pass on a future owner) . Here's same drawing digitally "cleaned up" a bit with English translations added & saved as a jpeg.

Shaft Log jpeg.jpg

[tribologist]

The keel is filled with vermiculite and polyester. It would be a total nightmare to get the old tube out. Personally I would strongly advice against that project. The stern tube has nothing to do with the rotordynamics. Well over 1000 boats been built and operated with the stock tube. The problem many people have is that they replace the stock combo bearing/seal with a PSS Dripless seal that has 0 or even negative stiffness and 0 damping. (That includes our Driftless that is fitted with a 1” shaft when repowered. Driftless has a bearing mounted infront of the seal to eliminate shaft whip. When the time is up for the dripless Im making a 1” version of the original shaft seal.

[Armatore]

Thanks Tribologist. That's what I suspected, that the keel was filled with the mixture. I have constructed the new shaft tube but I think I will just replace the old shaft to get by for this summer. I'm still checking my shaft to make sure it is straight. Good idea about an intermediate bearing to deal with any shaft whip. My setup with the Python Drive has a massive thrust bearing only 8-10" forward of the traditional shaft log.(Not a dripless seal) Maybe something will have magically cured itself over the winter. Thanks again

[tribologist]

My guess is that it is something else. Maybe just aligning the mounts again? Does the transmission really need a thrust bearing? What is the powerplant in it? Here is the arrangement we have in Driftless. It is just a split grease lubed bearing. Not that great but it has been holding up fine. I grease it each day with a tiny squirt from the grease gun

[WillieC]

For the 30mm stock shaft in our A25, the boat came with a PSS, the shaft whip seemed to me to be an issue since it was a long way from the engine to the cutlass bearing. This was about the time I was learning about failed oil saturated engine mounts and how to properly align the shaft after installing brand new mounts. In my ignorance, I thought that it was normal for the PSS to rise and fall a quarter inch each revolution. I found a cutlass bearing for Beneteau sail boats that was just the rubber piece, no bronze attached. I shortened it up and stuck it in the stern tube just aft of the PSS bellows boot and held it in place with a few daubs of 291, I think. (It was a snug fit, I just didn't want it to start spinning.) Apparently the original traditional stuffing box also served as a somewhat bearing point, which as noted by others the PSS does not.

Our new(er) boat has a Buck Algonquin old school stuffing box which I am getting used to. I think I prefer it. Ask me in ten years.

[Armatore]

Thanks again guys. I will try to take and post a pic of my installation. I had to replace the original Volvo MD-17C due to the fact that the P.O. let it freeze without draining. Water jackets all cracked and a bondo repair had no chance! I found a Universal/Westerbeke M35 out of a wrecked Catalina sailboat and I think I lucked out...it seems to run like a sewing machine. I decided to install a Python Drive coupling to with a rigidly mounted thrust bearing to isolate the engine from from the shaft thrust and allow for soft engine mounts to minimize engine vibration transmission to the hull. So far it hasn't worked so well. I'm still getting a lot of vibration at certain rpms. Last summer two things happened. One, the rubber isolating bushings on the thrust bearing broke down so that the alignment of the thrust bearing was compromised. Number two: the shaft vibrated sufficiently that it wore a powder of bronze from the "old school" Buck Algonquin style stuffing box. (Which I like very much). All this is on my new 1.25" shaft. Before recommissioning this spring I will realign the thrust bearing and check the shaft for straightness. With the Python Drive no need to align engine since there is a cardan shaft between the thrust bearing and transmission that requires at least 7 degrees mis-alignment which I have. Thanks for all your suggestions. I will definitely postpone installing a new stern tube for another year and see if I can't get things smoother with the above tweaks. Cheers

[tribologist]

Requires at least? Is that to make sure its lubed?

[Armatore]

Tribologist,
Yes. The manufacturers directions require that much mis-alignment to keep the bearings of the cardan shaft lubricated.

[DesertAlbin736]

I decided to install a Python Drive coupling to with a rigidly mounted thrust bearing to isolate the engine from from the shaft thrust and allow for soft engine mounts to minimize engine vibration transmission to the hull. So far it hasn't worked so well.

Owners previous to us re-powered the original AD21 with a Yanmar 3GM30F back around 1990-ish and added an AquaDrive combo thrust bearing and CV joint coupling with soft engine mounts. Runs much quieter and practically vibration free than other Albin 25's I've been aboard. Only instead of mounting the thrust bearing unit straddling the keel sump just ahead of the stuffing box ours is mounted inside the engine box just aft of the CV joint and bolted directly to the engine bed plates via custom fabricated angle iron. Our 3 cylinder engine 'shakes' a bit at low idle RPMs less than 1,000, but smooths out above 1,000 RPM. Something to do with harmonics I suspect. The CV joint allows some toleration of slight misalignment between the transmission and thrust bearing, and of course the flexing of soft engine mounts. Luckily we haven't had any issues with the stern tube.

DSCN3674.JPG