Shaft log and stern tube advice wanted

K

KenMcCulloch

Well-Known Member
Joined
22 Apr 2007
Messages
2,786
Location
Edinburgh, Scotland
Visit site
I am having to lift Border Maid out of the water at the weekend as a significant trickle of water is coming in from around the stern tube. This is NOT a gland problem, the water is coming in around the outside of the stern tube, not around the propshaft itself.

The shaft is offset, inboard it goes into a big block of wood fastened to the planking and the adjacent floor. Outboard is a metal shaft log (bronze I think, never actually investigated) with a cutless bearing in the outer end. This installation probably dates from the 1960s when a Stuart Turner engine was fitted in what was originally an engineless boat. I am assuming that the water is coming in at the cutless bearing and leaking out of the stern tube and finding its way into the boat that way.

What I would really appreciate is any advice from someone who has dealt with a similar set up. I'm particularly interested in knowing how the shaft log and the tube carrying the inboard gland are connected up, as the leak must be somewhere between the packing gland and the shaft log
 
I'm particularly interested in knowing how the shaft log and the tube carrying the inboard gland are connected up, as the leak must be somewhere between the packing gland and the shaft log
**************************************************

Nop........Willing to bet the water is leaking up outside the stern tube between the tube and and the wooden block and or hull.

Any water that comes up through the cutless bearing would leak in through the seal.

The stern tube should be a watertight entity between the cutless bearing and shaft gland/seal.

The stern tub could be two components screwed together and if there is a flange at the cutless bearing then rotating this may screw off the aft section allowing the inboard section into the boat. Oh dear.....Engine oot.

You would have had this PLUS a coffee the other night .

/forums/images/graemlins/laugh.gif
 
Sounds like a Stuart Turner stern tube. In which case it will be a bronze tube, threaded at either end and a "drive" fit through the wood. The outer bearing housing is screwed onto the tube and sealed - I usually use a ring of caulking cotton and polysulphide sealer (Boat Life). It is probably this seal that has failed allowing water to creep up between the bronze tube and the wood. The bearing housing is "dogged" into place with two bronze screws, probably cunningly hidden under years of antifouling. Remove these screws - I use a substantial driver with a hex shaft and a spanner. Undo the bearing housing - large adjustable wrench or Stilson required. Don't worry about damage, it is a robust casting. Replace the bush - if it is original it is a 3 5/8 long fluted rubber bush, probably available from T Norris. Or, if you are thinking long term have it sleeved to take a standard cutless, which you will need to shorten from its standard 4 inches length. Re assemble with loads of sealer and job done for your lifetime!

Guess who has done this job before.

You may also want to consider having the inboard end, also screwed on machined inside to remove the white metal bearing and replace with a length of cutless, and outside to take a Volvo seal. Then no more drips and a much better job.
 
Does this help. It sounds like it's installed inside out!

scan0002-3.jpg
 
I've sometimes suspected a similar thing happening with my boat, likewise with a traditional stern tube set up.
I think what happens is that water correctly gets past the rear bearing, and then fills the space in the tube around the shaft.
The packing at the front stops it coming out along the shaft (apart from the desirable few drips).
The tube is inside a long hole in the wooden log, with some kind of void space around it. All that stops the void filling with water is the thread on each end of the tube where the respective bearings screw on. Even wth a tight gland at the front, and the rear bearing housing sealed into the sternpost or whatever, the threads themselves remain a weak point. Water can pass from the shaft side, round the screw thread spiral, and into the void. Once in the void it can follow any seams and joints it can find, so can trickle out somewhere else.

One trick I have read is to drill a hole from the side into the log, being careful not to puncture the bronze tube, then expoxy in a grease nipple. The whole void can then be pumped full of some kind of (non-setting) filler. Very thick grease might do.
 
I would guess at a failure of the stern bearing/shaft log joint first rather than the threads and it's a resonably easy job to unbolt the bearing and unscrew it for rebedding.

Here the stern bearing is removed - tube is still in piece up there and as you can see perfectly dry (I had mechanical damage to the exterior of the stern bearing - big hole is a deadwood bolt!). The photo does illustrate the 'void space' raised by Clifford.

122-2265_IMG.jpg


122-2299_IMG.jpg


123-2314_IMG.jpg
 
Excellent photos. If it is a Stuart Turner, the housing will be longer, slightly tapered and the flange flat against the deadwood.

On my boat the actual tube is a really tight fit and does not appear to have a void around it. One of the reasons why it is still there but modified to use cutless bearings is the difficulty of removing it!
 
Thanks for these very helpful observations. I should emphasise that his is an offset prop setup, not through the sternpost, with a bronze (?) shaft log rather like the illustration in Tillergirl's post on the outside. We are craning out tomorrow and my friendly local boatbuilder is on the case.
 
Reminds me of a similar problem on my old boat 5 years ago. I was on passage back to Plymouth after being laid up afloat in Exeter, as there was little breeze I was motoring and, after an overnight stop near Brixham the night before I (fortunately) decided to anchor for lunch in Starehole Bay. As soon as I stopped the engine I could hear water cascading in, lifting the bottom boards found it was coming in near the shaft. I frantically timed the pumping rate needed to cope with it - about 5 mins pumping every 15 mins and decided to carry on for the Tamar at full speed as once in Salcombe repairs could well prove costly. By the time I beached her at Saltash pumping was up to 10 mins every 15 - more water was coming in and my arms were getting tired. Got craned out at Polbathic the next day.

The shaft was slightly offset with wooden logs inside and out, vibration from the badly worn shaft and bearing (yes I knew about it but it had only got slightly worse over the preceding 14 years) had shaken the log fastenings loose and it was all coming adrift. No other sailing that year as needed new shaft, repairs to deadwood fastenings and re-metalled bearing (not a cutless one!). While it was all apart I did however find evidence confirming a prop shaft wasn't fitted when built.
 
Yes, I had appreciated that you were talking about a quarter installation. I had one on my first boat - in fact I refitted it on replacing the Stuat Turner with an Albin. If it is a Stuart shaft log, its kind of odd to have it on the outside as the point of it was that it was adjustable to an extent to help line up the engine.

Good luck
 
I have had the same set up on two previous boats.
As has been suggested one simple way to reseal the tube to log is to use a mix of redlead puty and grease. A 6mm dis hole can be drilled in the log to the tube and the coach screw wound in sufficiently to hols it tight The putty/grease mix can then be injected to the tube /log joint. I used a coach screw abot 10 mm dia, drill a 3mm hole down its center, fix a grease nipple to the flat head and pump in the goo. Do it carefully as it produces a lot of pressure. Stopped my log /tube leak permanently.
 
Kens boat started life with a Sturt Turner......I am wondering if the Yanmar now fitted and with flexible mounts is giving unwanted forces on the timber arrangment for the through hull. Time will tell. May need a flexible shaft coupling if not fitted.
 
[ QUOTE ]
Kens boat started life with a Sturt Turner......I am wondering if the Yanmar now fitted and with flexible mounts is giving unwanted forces on the timber arrangment for the through hull. Time will tell. May need a flexible shaft coupling if not fitted.

[/ QUOTE ]
Yes I think there's something in that. The original ST engine will have been solidly mounted and the stern gear set up to suit. There is an R&D plastic flexible coupling in the drivetrain, presumably for exactly that reason, and little or no movement is observable at the inboard gland but I have been suspicious of the whole setup for a while. The current plan is to reseal around the stern tube and the stern tube / external shaft log / hull joints and to consider improvements to the isolation of the shaft from engine movements and / or an inboard seal with greater flexibility at the next refit.
 
The flexdrive will help but those one lungers shake all over the place at certain revs and I can imagine the leverage effect on the outboard sterntube wooden housing. About all you could do is fit an Aquadrive however I suspect room would be a problem. Have to have a sneeky peek and think about it!
 
If you are going down that route then my solution in my earlier post is worth considering. It is the Mk 3 version and so far has proved good. Modify the bearing housings to take cutless bearings and a Volvo seal. Replace the R&D with a Vetus Bullflex coupling. (My Mk1 had a rigid coupling and no inner bearing in the tube - hopeless. Mk 2 was modified stern tube, R&D and Volvo seal. Bullflex was Mk 3). further improvement, but only to reduce the rocking of the engine at low revs might be more resilient mounts, but at £325 a set will wait until the Yanmar ones fail.

Hope this helps
 
You don't have to modify the housing to take a cutless bearing, Countrose Bearings do one to standard Stuart Turner dimensions (not listed, you have to ask for it) It's a composite and rubber one rather than brass and rubber. I replaced mine last year after most people told me they no longer existed.

John
 
Thats interesting. Mine was modified (it needs to be sleeved to accept the smaller OD of a standard bearing) in 1992 by Lake Engineering because there were long term doubts about supply of the ST bearing - although I think it is still available. Removing the white metal at the inboard end and replacing it with cutless is still, I think a good move if used with a Volvo seal - no more drips and grease!
 
well you learn something new every day, My Eventide has a shaft log and i think the outboard bearing needs changing, how do i know what type of bearing i need? the bearing housing is very similar to the one in the pic and it used to have a stuart turner before i bought her, i can just about remember the last time she was out of the water i took the prop shaft out and ran my finger inside the housing and i think it was just metal /forums/images/graemlins/confused.gif.
 
Almost certainly will be an ST tube. Recognition points are large double nut for stuffing box on inboard end screwed onto a bronze casting which in turn is screwed onto the end of the tube and dogged into position with two Bronze woodscrews. The inside of the bronze casting is lined with white metal. The outboard end is a bronze casting just under 4 inches long with a couple of water inlets on the front face of the flange. Again screwed onto the tube and located on the deadwood with two bronze woodscrews. The outer bearing is a fluted rubber bush which is still available, I think, or the special cutless replacement mentioned above.

Hope this helps.
 
You must log in or register to reply here.

Other threads that may be of interest

ianc1200
Sureseal shaft seal.
2
Replies
20
Views
516
ianc1200
ianc1200

Share this page

Top