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Leaking stern tube

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rogerfg7 View Drop Down
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Post Options Post Options   Quote rogerfg7 Quote  Post ReplyReply Direct Link To This Post Topic: Leaking stern tube
    Posted: 25 May 2013 at 8:02pm
Second attempt at posting as previous one seems to have disappeared, or maybe it needs aproving firast.

My stern tube seems to have developed a leak.  I have just put the boat in the water and the bilges are filling up with water in 48 hours.  After checking usual culprits, sea cocks, stern gland and mast, I found after removing the rubber tube from the stern tube that water was leaking between the stern tube and the bonding around it.  Moongirl posted on 15 Apr 2013 at 7:51p that the stern tube is 'glassed in - just occasionally the bonding needs to be replaced'.

Presumable this is what is needed.  Does anyone know what is involved in doing this, is it a rudder off, prop shaft out job or can it be done with prop shaft in-situ.

Many thanks, Roger
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George Isted View Drop Down
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Post Options Post Options   Quote George Isted Quote  Post ReplyReply Direct Link To This Post Posted: 28 Oct 2013 at 5:25pm

Hi Roger,

Just found this post while doing some research, having spent some time at the back of the engine on Sunday (gosh I know how to have fun!) I think I also have a slight leak on the same place (between the stern-tube and it’s bonding to the hull).  It doesn’t seem to leak with the engine off but with the engine running the vibration/movement lets a very small amount of water in.

 

What’s actually holding the stern tube in place?   Is it just a bit of bonding on the inside + some sealant around the outside flange (looks like two large machine screws going through a flange and into the skeg).

 

I need to replace the cutlass bearing this winter so it looks  like I have another job to add to the list.

George Isted
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waratah912 View Drop Down
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Post Options Post Options   Quote waratah912 Quote  Post ReplyReply Direct Link To This Post Posted: 28 Oct 2013 at 6:24pm
If you're spending time around the back of the engine, sticking a couple of LED strips to the underside of the cabin sole makes a huge difference. I also stuck a couple on wood battens to increase illumination down the sides of the engine or wherever else I wanted it. 
At £3 for two you can't go wrong, and they seem to survive extended engine running.
I wonder how much they'd be in a Chandlers???
Paul Smith
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George Isted View Drop Down
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Post Options Post Options   Quote George Isted Quote  Post ReplyReply Direct Link To This Post Posted: 28 Oct 2013 at 6:28pm
Hi Paul, good idea, I think that may be part of "engine bay stage 2" that includes replacing the aging soundproofing.
George Isted
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Post Options Post Options   Quote moongirl Quote  Post ReplyReply Direct Link To This Post Posted: 03 Nov 2013 at 11:21pm
George
Have a look at my Sterngear Arrangement drawing! Looks like you have the 'older' arrangement where a plate holds the bearing via 2 bolts. On Polar Star we found that the GRP bit where the shaft enters the hull had slightly broken away & needed to be re-glassed to cure a leak - not a major job if the area is dry & you are slim enough.
Regards
COLIN
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Post Options Post Options   Quote George Isted Quote  Post ReplyReply Direct Link To This Post Posted: 04 Nov 2013 at 9:31am

Thanks Colin, I had another look yesterday and the bonding around the tube in the engine bay does appear to be very slightly lose allowing a small about of movement when the engine is running (the 2GM bounces around a bit at low RPM) but it's hard to tell if water is getting in or not, it could just be the stern gland needs tightening a smidge.

 

I had looked at your drawing and it suggested that the plate on the outside of the skeg is brazed to the tube so cannot be removed (unless the whole tube and end-plate can be pulled out).  However, your comment suggests that plate can be removed on its own to remove and replace the bearing, therefore not brazed to the tube?

 

From memory my bearing is just pushed into the rear of the stern tube so with the shaft removed it should be (relatively) easy to pull out and swap for a new one.

 

Any thoughts...

 

George

George Isted
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waratah912 View Drop Down
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Post Options Post Options   Quote waratah912 Quote  Post ReplyReply Direct Link To This Post Posted: 04 Nov 2013 at 10:06am
George,
As with all things Contessa your key phrase is "should be (relatively) easy". Maybe you should add "but never is".
I've had to do this several times before I discovered the shaft had been replaced with a 25mm one not the standard 1 inch version! The simplest way I found to do it is to use a hacksaw blade to cut about a 3 mm strip out of one side of the bearing and then cut opposite and the bearing collapses. An alternative that some previous fitter had used on Waratah is to cut off the flange and simply drive the old bearing up the stern tube! To remove that necessitate construction of a drive tool from broom handle to go through the bearing and washer to mate to the bearing and then drive the whole lot out from inside.   
I repacked the stern gland last winter and oh joy, much less water in the boat, maybe two or three strokes of the pump each month, and I suspect most of that is rain down the mast. 
Paul Smith
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Post Options Post Options   Quote George Isted Quote  Post ReplyReply Direct Link To This Post Posted: 04 Nov 2013 at 11:05am
That's a good point and very true Paul, note use of "should" and "relatively"!
George Isted
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Post Options Post Options   Quote rogerfg7 Quote  Post ReplyReply Direct Link To This Post Posted: 04 Nov 2013 at 11:52am
George

Just got your post.  I did have a leak between the stern tube and the rear engine bulkhead.  The boat had to come out of the water and the prop shaft removed.  We used a radiator pressure testing kit courtesy of Fox's Marine Ipswich and pressurised the prop shaft to confirm that there was in fact a leak from the stern tube into the skeg void and thence into the engine compartment via the stern tube bonding.  We had to remove the stern tube via a puller arrangement (can provide photos) source a replacement stern tube in GRP, drill & file out the existing through hull holes to fit the larger diameter, cut out a panel in the floor of the cockpit locker above the skeg and clear out the void.  I then fitted and expoxied in the stern tube, paying particular attention to getting the alignment with the engine as close as possible to the required tolerances.  The skeg void was then filled with resin to prevent any further possibility of leakage, but making future removal of the stern tube impossible! Final engine coupling alignment was then carried out (Beta 20HP +/- 5 thou runout).  I can provide photos if required.  The problem seems to arise from those 2 screws above and below the cutlass bearing. Jeremy Rogers says never to touch them as they are only location bolts and only go into a thinish part of the skeg layup.  Once the seal is broken by moving them, water gets into the skeg void and without galvanic protection even the phosphor bronze eventually corrodes to the point of failure.  I can confirm that on my boat the end plate with the 2 bolts is an integral part of the stern tube.
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Post Options Post Options   Quote moongirl Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 2013 at 10:12pm
Hi George
Previous post is correct. The bolts just locate the tube.
The bearing is an interference fit into the end of the bronze tube.
One definitely does not want water in the Skeg as it's GRP over foam & we all know what happens to the old foam in rudders!
I think the explanation regarding water is that some passes between the tube & prop shaft then leaks through any small breaks in the GRP.
Regards
COLIN
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