extend a stuffing box hose?

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madmat99

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Hi all.
so. the situation i am in.
bought the boat, rebuilt the engine and its running great. got it booked in to be lifted back into the boat and thought, i better replace the packing glands i the stuffing box. (sorry if aim using any wrong terminology)
pulled out 6 bits of square section string from the box. its a 2 nut type not a threaded packer if that makes sense. looked at the prop shaft and its a right old mess, pitting galore, i would say in places up to half a m deep. however the rest of the shaft between the box and the gearbox is in great condition.
so i thought, great, i will just get a longer piece of hose and all will be well, i have loads of free length on the prop shaft and nice stainless jubilee clips. so i cut off the hose that was on and sprayed the propshaft/gearbox coupling bolt with some double TT to shift these in the morning.
BUT. it was only when i cut of the hose (which seemed fairly thin from all have read about using reinforced tubing (maybe 4mm)) that i saw that the hull ad the stuffing box were located together with a notch/spline/slot. so 2 notches on the hull side and 2 notches on the stuffing box. so 90 degree segments fitting into each other.
the question being if i extend the hose will it matter that the two are not now mechanically locked together and are just relying on the hose for ant twisting?

i hope this all make sense and thanks in advance for any answers.

Mat
 
There are some stuffing glands which rely only on the hose to prevent twisting, but the interlocking type like yours is superior so it seems a shame to lose that feature. Especially since you'd be relying on a longer bit of hose to resist twisting - how much longer are you making it?

My gut feel is that the extension would probably be ok provided you use the proper strong hose, but I also wonder whether it's necessary. Was the gland leaking before?

Pete
 
i would be adding 3 inches to the hose to get the box past the pitting on the shaft. unfortunately that would take the splines out of contact. i have had the boat a few months and bought it from a hard standing so have no idea if it was leaking or not, i don't have much experience with prop shafts but this thing looks terrible at the contact point and i think it would just chew up new packing..
 
Two sensible alternatives. First and easiest (and probably cheapest) is a new shaft. Second, but requires a bit more thought working out which will fit is replacing stuffing box with a modern seal that either uses a different part of the shaft or does not make the seal on the shaft.
 
I imagine a 3” extension to the hose would be okay if you use quality hose designed for this purpose. No doubt the suppliers could advise as to the maximum permitted length.

A better solution would be to reverse the prop shaft end for end, which I appreciate might require additional machining work. If you can do this, it would be a mechanically superior solution and should allow you to retain the positive interlocking of the shaft log components.
 
Another alternative if you have the right type of engine to propshaft coupling is to cut 3" of the end of the shaft and slide the propshaft forward but check the propeller clearance is ok with being moved forward.
 
I would think that extending the hose by 3" would be a bit risky as you're then transmitting all the torque through it. The suggestion to change the prop shaft is the one I'd take as you can then retain the interlocking 'dogs' to transmit the torque which is a much better solution. New shafts are not particularly expensive.
 
How long would the hose be in total? Mine is about 6 inches with no interlocking splines. It's a serious piece of rubber though. Purpose made from Portmererubber.co.uk It all works fine. There would only be a bit of twisting if the shaft was too tight in the seal.
 
What would happen if the prop caught a rope or something? Partners supplies approved hose 'the best a man can get'.
Spyro said:
How long would the hose be in total? Mine is about 6 inches with no interlocking splines. It's a serious piece of rubber though. Purpose made from Portmererubber.co.uk It all works fine. There would only be a bit of twisting if the shaft was too tight in the seal.
Click to expand...
 
Billba said:
You speak of two notches on the hull side. Would it be possible to duplicate those notches in the new position? Also I would ensure the tube you intend to use is of the required grade. Scroll down third from the end... http://www.tnorrismarine.co.uk/product/hoses-and-tubing/
Cheers Bill
Click to expand...
I assume that the notches engage with each other, like a dog clutch. Extending the length of the hose would mean that the "dogs" miss each other. It would be possible to make an internal steel tube device, with the ends castleated to fit into the existing notches, but far better just to bite the bullet, and fit a new shaft.
 
There are photos of the locking arrangement, and the consequences of using the incorrect hose, on my website at https://coxengineering.sharepoint.com/Pages/Sternglands.aspx As has been said, this hose is specialist stuff and using exhaust hose or something similar is not to be recommended. There can be quite a lot of frictional drag between the gland and the shaft, which might well be too much for such a long extension without mechanical locking.
 
I do not seem to be able to connect to Vyv's site. Always worked before and Vyv confirms his end looks fine, Anyone else having problems? Cheers Bill
 
insert a spacer between coupling and the gearbox flange to move the shaft 1" (or whatever) further out. If you've enough space between prop and rudder. This leaves the sterngland untouched with all its dog locking devices intact, the correct length of hose and the packing running on a new bit of shaft.

Or as NormanS says, fit a new shaft...
 
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