One for the metallurgists. Rudder shaft

[geem]

A friends here in the boatyard at Curacao Marine has removed his rudder. Cracks in the grp layup around the top of the rudder shaft were the first sign of an issue. Cutting out a section of the grp reveals what looks like crevis corrosion. The boat is a 2001 Jenneau deck saloon. The rudder shaft is solid stainless steel of about 60mm diameter.
The question is how to repair it? Can it be repaired? If the crevice corrosion is ground out with a die grinder and the holes welded up and ground smooth will it be sufficiently strong? The corrosion is just below the bearing so there isn't sufficient space to sleeve the shaft. What is the expert opinion?

 

[vyv_cox]

I have seen a few problems with Jeanneau rudder shafts. All I have seen were duplex stainless steel, which attracts a magnet, so worth checking. I agree it looks like crevice corrosion and the location would be typical but I suggest you carry out very careful measurements in case of electrolysis. Two of the cases I looked at were due to minor electrical faults that gave the shafts positive potentials.

It is possible to weld repair duplex s/s but not straightforward. Here is a link that says it all Welding metallurgy of duplex stainless steel.
And this one
https://www.engineersaustralia.org....uplex_Stainless_Steel_Mechanical16April09.pdf

If it does not attract a magnet it is likely to be 316. In this case a weld repair is possible, using 316L filler. It goes without saying that the welder should be highly competent for this critical application.

 

[Fr J Hackett]

As the saying goes, you need good penetration, in the weld.

 

[vyv_cox]

As the saying goes, you need good penetration, in the weld.

Always good advice.

 

[geem]

I have seen a few problems with Jeanneau rudder shafts. All I have seen were duplex stainless steel, which attracts a magnet, so worth checking. I agree it looks like crevice corrosion and the location would be typical but I suggest you carry out very careful measurements in case of electrolysis. Two of the cases I looked at were due to minor electrical faults that gave the shafts positive potentials.

It is possible to weld repair duplex s/s but not straightforward. Here is a link that says it all Welding metallurgy of duplex stainless steel.
And this one
https://www.engineersaustralia.org....uplex_Stainless_Steel_Mechanical16April09.pdf

If it does not attract a magnet it is likely to be 316. In this case a weld repair is possible, using 316L filler. It goes without saying that the welder should be highly competent for this critical application.

Thanks Vyv, just checked the shaft and it's magnetic. There are welders here. We will check with them on Monday about the viability of a weld repair. Otherwise it may be a new rudder?‍?
Just checked the top rudder tang. The tang isn't magnetic buy the weld is. Different grades of stainless used by the looks of it

 

[Keith 66]

By the time you have ground the corroded area out there is a real risk of the rudder shaft warping (bending) with the welding stresses.

 

[geem]

By the time you have ground the corroded area out there is a real risk of the rudder shaft warping (bending) with the welding stresses.

Maybe, but from what we can see now, the hole is not so deep. I don't know enough about this kind of corrosion to know how deep it will go. If it is only as deep as what we can currently see then I can imagine that filling the hole with weld would warp the shaft.

 

[Neeves]

I'd be running a parallel investigation to source and cost a new shaft and all the implications (complete new rudder?). Sleeve and new bearings? Once you have all the information a decision can be made on which way to move.

The focus seems to be restricted to repair and I'd be twitchy about Vyv's comment on 'expertise'.

I hate to simply throw money at an issue but the comfort of knowing it is a new shaft (which might be carbon?) might merit some extra cost. It is were me I'd like all the costings and all the options, as far as possible.

Your friend is lucky - he has you and the extended expertise available and need not be fobbed off with the 'spend money' option.

Jonathan

 

[geem]

I'd be running a parallel investigation to source and cost a new shaft and all the implications (complete new rudder?). Sleeve and new bearings? Once you have all the information a decision can be made on which way to move.

The focus seems to be restricted to repair and I'd be twitchy about Vyv's comment on 'expertise'.

I hate to simply throw money at an issue but the comfort of knowing it is a new shaft (which might be carbon?) might merit some extra cost. It is were me I'd like all the costings and all the options, as far as possible.

Your friend is lucky - he has you and the extended expertise available and need not be fobbed off with the 'spend money' option.

Jonathan

I don't think sleeving is an option. The bearing is 15mm above the site of the corrosion.
The owner has already contacted Jenneau in the US and France with a view towards a complete replacement rudder as an alternative solution. They are planning a Pacific crossing so the solution needs to be right and strong.

 

[penfold]

Unless the GRP is badly wrecked there's no reason you couldn't get a fabricator to make a new stainless steel rudderstock armature and have a laminator bond the grp over it; may be cheaper/quicker than from Jeanneau.

 

[vyv_cox]

Thanks Vyv, just checked the shaft and it's magnetic. There are welders here. We will check with them on Monday about the viability of a weld repair. Otherwise it may be a new rudder?‍?
Just checked the top rudder tang. The tang isn't magnetic buy the weld is. Different grades of stainless used by the looks of it

Yes, there would be little point in using a high strength stainless for the tangs. A 300 series is perfectly adequate .

 

[Keith 66]

Yes, there would be little point in using a high strength stainless for the tangs. A 300 series is perfectly adequate .

I would not consider that adequate on my boat. GRP rudders always get water in them after a while, particularly if they are foam filled as many are. (dont know if the Jeaneau's is)
Using disimilar metals or grades of metals for tangs is not a good idea as the low oxygen waterlogged environment will invite corrosion.
Ordinary 304 grade is likely to corrode as fast as mild steel in those conditions.
My own boat (Sabre 27) had mild steel tangs in its rudderstock, a penny pinching job by Marcon, result was two tangs broken completely & the last hanging on by just 4mm of weld.
As said by Penfold a good & quite likely cheaper option is to split the rudder & just fit new stock & reuse the rudder shells.

 

[Daydream believer]

Try Jefra as they make rudders for many of the major manufacturers & can supply withing 4 weeks for some types.
Mine was supplied within 3 weeks, when I lost my rudder & it fitted almost exactly. Original was a polish badly manufactured one.

 

[vyv_cox]

I would not consider that adequate on my boat. GRP rudders always get water in them after a while, particularly if they are foam filled as many are. (dont know if the Jeaneau's is)
Using disimilar metals or grades of metals for tangs is not a good idea as the low oxygen waterlogged environment will invite corrosion.
Ordinary 304 grade is likely to corrode as fast as mild steel in those conditions.
My own boat (Sabre 27) had mild steel tangs in its rudderstock, a penny pinching job by Marcon, result was two tangs broken completely & the last hanging on by just 4mm of weld.
As said by Penfold a good & quite likely cheaper option is to split the rudder & just fit new stock & reuse the rudder shells.

I think you may have unrealistic expectations as regards builders' material choices. I know of many boats that have carbon steel tangs welded to stainless shafts. It would be amazing to think that Jeanneau or anyone else would use an expensive duplex grade for such a humble duty. A 304L tang would last for decades and even a 304 would be good for a long time.

 

[burgundyben]

I guess we moved away from bronze due to cost.

 

[Beneteau381]

I guess we moved away from bronze due to cost.

My Bene 381 is a big fat glass shaft

 

[burgundyben]

This thread made me wonder about a composite replacement.

 

[Neeves]

A stock and tang are in an oxygen deficient environment and I would have thought when a rudder is built it would not be expensive in either labour nor materials to coat the whole thing, stock and tangs, with resin and glue the foam, glass and filler to the coated metal work.

But I'm no boat builder with an accountant breathing down my neck.

Noting Benny381's and Ben's post - carbon seems to be a way to go. Off the shelf carbon tubes....?

Lightwave cats have carbon stocks and I assume carbon tangs.

In this case - have the stock and tangs made up (by Jenny or A N Other) in carbon and simply, or less simply, add the existing or a clone of the blade, It would not be difficult to make up the profile of the blade, if you can access foam, glass and resin - assuming it is in good condition (and there has been no report of damage).

Jonathan

 

[geem]

I would not consider that adequate on my boat. GRP rudders always get water in them after a while, particularly if they are foam filled as many are. (dont know if the Jeaneau's is)
Using disimilar metals or grades of metals for tangs is not a good idea as the low oxygen waterlogged environment will invite corrosion.
Ordinary 304 grade is likely to corrode as fast as mild steel in those conditions.
My own boat (Sabre 27) had mild steel tangs in its rudderstock, a penny pinching job by Marcon, result was two tangs broken completely & the last hanging on by just 4mm of weld.
As said by Penfold a good & quite likely cheaper option is to split the rudder & just fit new stock & reuse the rudder shells.

The cost quoted to do that here in Curacao is steep. It may be cheaper to get a new rudder.

 

[geem]

A stock and tang are in an oxygen deficient environment and I would have thought when a rudder is built it would not be expensive in either labour nor materials to coat the whole thing, stock and tangs, with resin and glue the foam, glass and filler to the coated metal work.

But I'm no boat builder with an accountant breathing down my neck.

Noting Benny381's and Ben's post - carbon seems to be a way to go. Off the shelf carbon tubes....?

Lightwave cats have carbon stocks and I assume carbon tangs.

In this case - have the stock and tangs made up (by Jenny or A N Other) in carbon and simply, or less simply, add the existing or a clone of the blade, It would not be difficult to make up the profile of the blade, if you can access foam, glass and resin - assuming it is in good condition (and there has been no report of damage).

Jonathan

I crewed on a 38ft all carbon race boat with carbon rudder shaft. It snapped. The quote for new was $10,000US. The way they build the carbon shaft is interesting. They take solid carbon rods and bunch them together then wrap them in carbon cloth. Difficult to make but theoretically strong. Not sure it's a viable build cost on a production boat