Stern tube repair thoughts

[misterjenkins]

Following an incident where our stern tube and prop shaft were bent whilst being lifted by the marina, I wanted to get some thoughts about the repair.

The engineer the marina asked to do the repair initially said that our stern tube needed replacing. We visited the boat today to look at the work done. Having been unable to remove the stern tube (it's bonded directly into the GRP - she's from the early 70's ), they have cut away the damaged end, fitted a sleeve and a new section to the end of the tube, rather than replacing the entire tube.

Is this an acceptable repair? The engineer and the marina are adamant that this is better than what was there before, but we're not so sure.

Would welcome your thoughts.

Photos below show the original bent tube and prop shaft, and the new tube and sleeve fitted.

 

[MoodySabre]

Ask your insurers to pay for a surveyor.

 

[RichardS]

Oh dear .... that's a sad sight to see. It's the kind of thing that I've often thought about as a possibility but I've never actually seen any proof that it can happen.

I've no experience with shaft drives but if the shaft is fully encapsulated in GRP and there is no sign of the GRP cracking then I'm sure that the stern tube inside the encapsulation must be fine. The repair looks good from the photos although it's not clear to me how the new extension has been joined to the old tube or whether the two tubes are simply butted up to each other and encapsulated. if that's the case, I would want a surveyor opinion about how effective that is.

Richard

 

[Tranona]

That looks sound if it is securely attached to the existing tube. However I would be very unhappy with that rope cutting disc as it is blocking water flow to the bearing. The original gap was there for that reason. If you want a rope cutter that works fit a proper scissors one with an extended shaft such thus a minimum 15mm gap is left after of the bearing.

 

[misterjenkins]

Interesting to hear your thoughts on the cutter. Propprotector (makers of this cutter) specify a 1/4 inch gap, which this just exceeds. Had hoped it was ok if it meets their spec

 

[RivalRedwing]

Ask your insurers to pay for a surveyor.

+1, a report from a surveyor may also prove useful if or when you decide to sell

 

[Pete7]

Surely if the engine is mounted on flexible mounts then it and the propshaft can move forward 1/4" when forward is engaged taking up all that gap and perhaps some more.

The solution might be a spacer at the gearbox end of the propshaft coupling. I have a Volvo one for sale on the for sale page.

 

[Tranona]

6mm is nowhere near enough clearance as the shaft can move back and forth as you go in and out of gear. That type of cutter is not particularly effective either.

Out of interest what caused that massive damage?

 

[misterjenkins]

We bought her in for a lift and scrub and she was lifted with the strop around the prop

 

[Heckler]

Following an incident where our stern tube and prop shaft were bent whilst being lifted by the marina, I wanted to get some thoughts about the repair.

The engineer the marina asked to do the repair initially said that our stern tube needed replacing. We visited the boat today to look at the work done. Having been unable to remove the stern tube (it's bonded directly into the GRP - she's from the early 70's ), they have cut away the damaged end, fitted a sleeve and a new section to the end of the tube, rather than replacing the entire tube.

Is this an acceptable repair? The engineer and the marina are adamant that this is better than what was there before, but we're not so sure.

Would welcome your thoughts.

Photos below show the original bent tube and prop shaft, and the new tube and sleeve fitted.

View attachment 71276

View attachment 71277

It looks like they have chased the glass to make sure the remaining tube is ok. I suspect that getting the tube out was not necessary once they had chased any damage. I would need proof of how they had secured the sleeve to the original. Also is the new shaft the same diameter? The spacing of the prop cutter depends on the make, see the fitting instructions for one here http://www.prop-protector.co.uk/information.php?info_id=2&osCsid=m7jkvnfeudt29q22b0c142faf2 Mine recommends 12mm on my Bene. The damage? caused by them putting the strop on the prop or the strop slipping off the keel?

 

[fisherman]

That sort of underwater repair can be completely sound..... or not. Definitely need it signed off by a surveyor. Is it insurance, or did the yard undertake to rectify off their own bat?

Local builder had to take a panel out of each hull of a cat to access duff stern tube fixings, so such work can be done, if done properly. From the pics we have no way of knowing what has been done in this case.

 

[Neil_Y]

Or the one the RNLI and Navy use?
Gap wise we have seen worst case movement on rubber mounts of 9.00mm fore and 9.00mm aft.

Our minimum allowance is thus a 12.00 gap between the spool and the bearing carrier be it a stern tube or P bracket.

This allows for 9.00mm movement and still a 3.00mm gap for water to exit the bearing. We have done tighter ones but usually based on looking at the actual amount of movement which can be seen as the polishing on the shaft. So a starting gap of 32.00mm works when the spool does not sleeve the prop. As a bearing supplier 3.00mm is OK for cooling water to exit the bearing.

 

[Akestor]

Hello. just very curious on how this repair was done.
Is it something like on the pic drawing?

or like this maybe?