One for the metallurgists. Rudder shaft

Yara said:
The question is- how are you going to stop further crevice corrosion? Maybe have a rough surface to allow oxygenated water to get to the area? As a cheapskate I would round the sharp edges of the larger hole, and add some vertical scoring to get the oxygen to the area. Welding and heat could make the corrosion worse when you do not know for sure what the shaft metal is. Then do a coastal cruise for a couple of weeks and check the site for further corrosion.
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I don't think Ben cares about further corrosion. The boat is 2001. Its taken over 20 years to get to this state of corrosion.
He will be selling once he has crossed the Pacific back to OZ. He just needs a solution that won't fail on the trip. A new one is likely to be 100% reliable. Repairing stuff here ( third world country) with very limited resources has its risks. There is one boatyard, one welder, two chandler's. Its not like being in the UK.
 
Unless you can find a welder or other repairer who says "I guarantee that my repair will result in the rudder being 100% ", then it's only the owner's attitude to risk that will decide what needs to be done.
As no repairer is going to give that assurance then there are two courses of action:

If the owner is risk tolerant, you could try the welding route or even simply use a very fine pointy Dremel bit to remove any sharp edges from the corrosion pits and if it still looks 'substantially like a rudder shaft', then fill the pits with Lanocote and head for Australia. "No worries mate, she'll be right!"

But given that the guy was checking his rudder prior to heading for the Pacific, then it's likely he is conscientious or even risk averse. Any sort of repair is likely to leave 'room for worry' and this can seriously degrade the enjoyment of any sailing from here on out. No reassurance from 'the on-line community' is going to alter the fact that only a new rudder is going to do it. Now whether you need a whole new rudder or simply a shaft and tangs for him to laminate into the existing shell can only be determined by his skills / pocket / resources. Foss are a manufacturer in the States who could probably supply what's needed. (Foss Rudders – Designer and manufacturer of custom and replacement sailboat rudders.).
 
He could get a suitable lump of stainless, preferably a round rod of similar thickness, get the welder to grind a similar sized hole to what would be needed in the shaft and then fill it with weld and dress it back to round. Then cut it and section it to check the weld for voids and penetration, if all is good go ahead with the repair if not seek another solution ie new rudder, leave it as is or go north to find a coded welder who could do the job properly.
 
The problem with all these suggestions is that the existing shaft is made from a length of duplex stainless steel that has been hardened and tempered to give it strength. Any heating operation that takes it to a red colour will destroy this heat treatment, effectively taking it back to an annealed (or normalised) condition.

The tensile and yield strengths of 2205, a typical duplex, are about 620 and 450 MPa. For an equivalent in the annealed state (316) they are about 550 and 240 MPa.

Thus, at exactly the point that most strength is needed, welding makes it weaker and more susceptible to bending, plus it reduces its fatigue limit.

Failing replacement by a new rudder my only suggestion would be to weld on a sleeve, a tube slit in two halves, assuming this will fit within the existing space.
 
Yara said:
The question is- how are you going to stop further crevice corrosion? Maybe have a rough surface to allow oxygenated water to get to the area? As a cheapskate I would round the sharp edges of the larger hole, and add some vertical scoring to get the oxygen to the area. Welding and heat could make the corrosion worse when you do not know for sure what the shaft metal is. Then do a coastal cruise for a couple of weeks and check the site for further corrosion.
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Crevice corrosion in this location comes about following a failure of the seal between the GRP rudder shell and the shaft. In this case the owner reports cracks but often there is no visible sign. the slight gap between the GRP and shaft allows water to creep in and you get the classic environment of static water trapped against the shaft. Remember boats spend most of their time stationary in the water - this boat is 20 years old and this is the inevitable result.

One solution is to leave a recess in the top of the GRP around the shaft and fill it with Sikaflex rather than rely on polyester to stick to the stainless. Some add an O ring around the rudder at that point as well. Another solution I used on a rudder I built with a stainless stock and an epoxy glass sheathed laminated wooded blade was to leave a recess in the top of the blade and had a 5mm thick washer welded to the stock which sat in the recess bedded in epoxy.
 
Fr J Hackett said:
He could get a suitable lump of stainless, preferably a round rod of similar thickness, get the welder to grind a similar sized hole to what would be needed in the shaft and then fill it with weld and dress it back to round. Then cut it and section it to check the weld for voids and penetration, if all is good go ahead with the repair if not seek another solution ie new rudder, leave it as is or go north to find a coded welder who could do the job properly.
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That was the kinda of thinking I had initially but the concern is getting a good weld
vyv_cox said:
The problem with all these suggestions is that the existing shaft is made from a length of duplex stainless steel that has been hardened and tempered to give it strength. Any heating operation that takes it to a red colour will destroy this heat treatment, effectively taking it back to an annealed (or normalised) condition.

The tensile and yield strengths of 2205, a typical duplex, are about 620 and 450 MPa. For an equivalent in the annealed state (316) they are about 550 and 240 MPa.

Thus, at exactly the point that most strength is needed, welding makes it weaker and more susceptible to bending, plus it reduces its fatigue limit.

Failing replacement by a new rudder my only suggestion would be to weld on a sleeve, a tube slit in two halves, assuming this will fit within the existing space.
Click to expand...
Great advise Vyv. Many thanks. I will pass this on to Ben
 
By way of an update. Jefa do a repair for the rudder problem. It would seem it's a known problem. If you have a 20 year old Jeaneau it would worth checking your rudder.
The repair kit seems to consist of a sleeve that is slid over the rudder stock to cover the area of pitting. The sleeve is about 115mm long. It is bonded in place not welded. Since the sleeve would interfere with the rudder bearing, Jeff's offer an alternative bearing arrangement that can accommodate the sleeve. It seems there are two sleeves available. One is 2mm thick. The other is 5mm thick. Since the pitting is 5mm deep on this rudder the plan is to go for the 5mm sleeve. Cost is circa €400 plus carriage to Curacao. A replacement rudder is more like €5k with carriage and about 5 weeks longer to obtain.
 
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geem said:
By way of an update. Jefa do a repair for the rudder problem. It would seem it's a known problem. If you have a 20 year old Jeaneau it would worth checking your rudder.
The repair kit seems to consist of a sleeve that is slid over the rudder stock to cover the area of pitting. The sleeve is about 115mm long. It is bonded in place not welded. Since the sleeve would interfere with the rudder bearing, Jeff's offer an alternative bearing arrangement that can accommodate the sleeve. It seems there are two sleeves available. One is 2mm thick. The other is 5mm thick. Since the pitting is 5mm deep on this rudder the plan is to go for the 5mm sleeve. Cost is circa €400 plus carriage to Curacao. A replacement rudder is more like €5k with carriage and about 5 weeks longer to obtain.
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See post 25
 
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