Extending shaft log tube

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ddalme

ddalme

Senior Member
Joined
Mar 6, 2015
Messages
451
Location
USA
Vessel Name
Relenti
Vessel Make
Atlantic 30, 1983
I'm getting ready to do a haul out and have the bottom cleaned and checked and change out a frozen sea cock, weld a broken dive platform brace, clean and polycoat, etc. Was also thinking about extending the shaft log inside the boat about 6" to facilitate easier access to the packing gland. The generator sits over it, making it very hard to work with. See any problem in doing so? Boat is a 1983 Atlantic 30 with a Volvo tamd40b engine. I have about 24" of shaft between the gland and the engine coupler.
 
How do you plan to extend it and keep the extension rigid? I replaced the tube in my charter boat when increasing the shaft size and in the process made it longer. But that's very different from adding to an existing shaft log.

Ted
 
I would glass another tube to the original and make a former that attaches at the joint and to both stingers. Heck, I could section the fiberglass tube and install without removing the shaft, but I want to change the hose on the gland also. So that's out.
 
Just you the correct hose and extend it. I see no need to extend the log. The box floats on the shaft so extending the hose 6" is no big deal.
 
Capt.Bill11 said:
Just you the correct hose and extend it. I see no need to extend the log. The box floats on the shaft so extending the hose 6" is no big deal.
Click to expand...
That would give me about 19" of hose. That's not to much? Am I over thinking this? Would be a lot easier fix.
 
ddalme said:
That would give me about 19" of hose. That's not to much? Am I over thinking this? Would be a lot easier fix.
Click to expand...

I've extended them several inches before to get the packing to ride on a smoother portion of the shaft with no issues. As I said the box floats on the shaft and there should be little twisting force on it. So with the correct stiff hose I see no problem.

But ask a shop or two that deals with prop shafts and see if they have an opinion.
 
Capt.Bill11 said:
I've extended them several inches before to get the packing to ride on a smoother portion of the shaft with no issues. As I said the box floats on the shaft and there should be little twisting force on it. So with the correct stiff hose I see no problem.

But ask a shop or two that deals with prop shafts and see if they have an opinion.
Click to expand...

Thanks Capt.-will do-this forum is awesome!
 
I don't see a problem with a long hose either but I'd call Buck Algonquin and talk to them first.
You'll need to use very heavy wall hose not just regular exhaust hose. Buck sells it but only in short lengths. While you're talking to them, ask if they can cut you a longer piece.
 
the shaft is positioned by the strut and transmission flange. The rubber hose mounting the packing system just stops the assembly from spinning and allows it to flex with the shaft if necessary. So like Bill I see no reason it cant be longer provide the hose is fairly stiff as they usually are. Can it be 2' long? My guess is that would be OK.
 
BEWARE !!

The hose used for shaft logs is a very special thicker heavy duty item


.It is NOT water hose or exhaust or toilet hose , but is a totally different product , and must be ordered as such.
 
FF said:
BEWARE !!

The hose used for shaft logs is a very special thicker heavy duty item


.It is NOT water hose or exhaust or toilet hose , but is a totally different product , and must be ordered as such.
Click to expand...

Roger
wouldn't do anything less
 
The hose on my boat approximately 2' long. This is on a 1.25" shaft. Not sure of the ID, but I'm guessing it's 3" or better OD.

The risk is torsional load on the hose due to packing drag.
 
If it was me ......I Would extend it with the extension of the F/G tube and re enforce as you suggested. It is done once and done properly. I would pre seal the ends of the cut tube before glassing.

Cheers Chris D Liberty Australia
 
I would extend the stern tube.

I think most stern tubes have a machined fwd end to accept the hose. If that's so on your boat get a FG stern tube piece that has the ID of the OD of the end of the stern tube that accepts the hose. If need be you could but a short piece of stern tube on the fwd end to mate w you're stuffing box ID. 5200, Marine Tex or some other epoxy could be used to "glue" these parts together.

Without the machined fwd end of the stern tube good alignment would be very difficult I would think.

Using a very long hose will transfer the bearing load that the hose and stuffing box provides (some to considerable depending on the hose and the boat) to the stern bearing and leave the shaft largely unsupported where some support previously was. If an intermediate bearing is close to where you want to terminate the stuffing box this wouldn't be a consideration but if it was a long way to the transmission flange (or the next intermediate bearing) shaft support may be lacking.
 
I'm going back to do some measurements and just from memory, I think I'll fiberglass an extension on the existing tube with support braces. That way I can get the proper hose and not be worried about a too long hose twisting, etc. on my shaft.
 
Can you get to it well enough to do a good glass job, or are you going to pull the gennie?

Another option would be to use a hose sleeve under the gennie to couple a FG tube to existing tube, then a second sleeve to couple the gland.
 
manyboats said:
I would extend the stern tube.

I think most stern tubes have a machined fwd end to accept the hose. If that's so on your boat get a FG stern tube piece that has the ID of the OD of the end of the stern tube that accepts the hose. If need be you could but a short piece of stern tube on the fwd end to mate w you're stuffing box ID. 5200, Marine Tex or some other epoxy could be used to "glue" these parts together.

Without the machined fwd end of the stern tube good alignment would be very difficult I would think.

Using a very long hose will transfer the bearing load that the hose and stuffing box provides (some to considerable depending on the hose and the boat) to the stern bearing and leave the shaft largely unsupported where some support previously was. If an intermediate bearing is close to where you want to terminate the stuffing box this wouldn't be a consideration but if it was a long way to the transmission flange (or the next intermediate bearing) shaft support may be lacking.
Click to expand...


You might be right. But I find it hard to believe a stuffing box on a flexibly hose add any significant support to a shaft. Especially when you consider how close the distance is between the coupler and the first bearing supporting the shaft in most cases.

The whole point of having the box on a hose would seem to be that it floats on the shaft and can move with it.

I would think if the box is going to add support it would have to be of the type that is hard mounted to a cross member and not free floating.
 
Support ...

Yes .. What I proposed would probably leave the tube unsupported and it could act like a tuning fork w it's own set of vibrations and possibly cause structural fatigue and perhaps failure.

By the way I suspect I have my terminology screwed up. Shaft log, stuffing box? What is the hole in the keel of a wood boat called? And there is the tapered bronze casting through which the shaft passes .. shaft log? Packing gland is the barrel shaped bronze tube like thing that we put packing in. But I think it's often or usually called the "stuffing box". The old wood boats of the 40's ect actually had a box like wood structure that I think the packing gland was lag screwed to via a flat plate that was part of the packing gland.

Many here know all this stuff. Would someone who does present the real propper terminology?
 
Last edited:
OK, what I'm talking about is the stuffing box. Not a strut tube with a bearing in it.

And since a stuffing box on a hose can't add much if any support to the shaft, that's why I've never been to concerned about extending the hose.
 
Capt.Bill11 said:
OK, what I'm talking about is the stuffing box. Not a strut tube with a bearing in it.

And since a stuffing box on a hose can't add much if any support to the shaft, that's why I've never been to concerned about extending the hose.
Click to expand...

Exactly, if anything it adds overhung load.
 
Agree with the just extend the hose 6 inches crowd.Nothing I see would change that much.

Sure you could glass..but that might be much harder and be totally unecessary.

Many people have extended or shortened their hose with no ill effects.

Try it as all the glass tube does is shorten the hose length...so if no additional wobble is noted...good to go! :thumb:
 
Oh oh,
I thought it was to be longer.
My bad
Yes 6" ... Just a longer hose.
 
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