Pitted Rudder Shafts

angus99 · Oct 31, 2015

I bit the bullet and had the yard remove and clean up the steering gear. There are no signs that water has ever leaked past the packing, but there had been leaks at the base of the bronze shaft logs, which had been "fixed" with a filet of caulk around the joint between the flange and hull, visible in the first two photos below. That kept the water out but obviously did not solve the problem. Miraculously, there is no rot in the wood reinforcing the hull penetrations and most of the gear cleaned up beautifully after bead blasting. That's the good news.

The bad news is some significant pitting on the steering shafts as you can see from the lower photos. I'd appreciate any knowledgeable recommendations about my options. It looks awful, but these are very robust shafts. I don't want to lose a rudder, but is that what I'd be risking if I have them reinstalled as is?

If I opt to get them fixed, is a prop shop the best option? Can anyone recommend a good shop in the northern Chesapeake who does this work well? (I'm not even going to ask about cost.). :banghead:

Gurryman · Oct 31, 2015

shaft repair

You have a simple shaft repair there. Being that the shafts are bolted to the rudders and easily removed, it is a Shaft repair, not a rudder repair. The shafts also seem to appear to be of sufficient mass to allow removal of the damaged area , build up , and machining. The mass works to your benefit as the larger mass will lessen the effect of heat input. Sorry don't know any shops in your area. TurnWright on Cape Cod could certainly do it. " I'm not affiliated with TurnWright, Although he did build the shaft and rudder on my Nauset".

rardoin · Oct 31, 2015

That certainly is more than surface pitting. I would be concerned that corrosion has occured between grain boundaries well beneath the surface. You would have to have a machinist turn down the shaft, build up, machine down the shafts. I would suspect the cost of fabricating new shafts (that will not be suspect in the future) may be in the range of a questionable repair. If you are in Penn. you will likely be able to find an oilfield machine shop that will take on the job for a very fair price as they are looking for anykind of work to keep their crews employed. I would certainly get a few bids on new builds.

Phil Fill · Oct 31, 2015

The pitting might be caused by galvanic action beteen the bronze and SS over time. So might want to added a bonding wire to the ruder shaft or a shaft zinc. Ss is rated less than bronze or brass. As for a repair might just use an epoxy to smooth out the area and check it next time you pull.

angus99 · Oct 31, 2015

Thanks for the replies. I got to see them for the first time this afternoon and no way are they going back on the boat as they are. The yard is investigating different techniques, including sleeving and "spraying" steel on them and machining back to original specs. They said new ones would be $800-900 each. :banghead:

gaston · Oct 31, 2015

angus99 said:
Thanks for the replies. I got to see them for the first time this afternoon and no way are they going back on the boat as they are. The yard is investigating different techniques, including sleeving and "spraying" steel on them and machining back to original specs. They said new ones would be $800-900 each.

Ask about hard chrome and grind to build the shafts up .I personally don't like steel spraying as it can delaminate when ever it want to .

psneeld · Oct 31, 2015

Had the best marine machine shop in the Cape May, NJ area (home to large sporty fleet and commercial vessels) flame spray my shaft 4 years ago.

3 round trips to FLA and back, 3 years r in salt water and all seems fine, Just repacked the stuffing box...shaft seemed fine and packing looked great.

Gurryman · Oct 31, 2015

"The Yard" is going to charge you double what ever they spend to repair them. Send photos and shaft dimensions to Keith Fenner at TurnWright, He will be able to give you a fairly good idea what a repair would cost. These are not high speed shafts and not a difficult repair.

What is the shaft diameter?

boatpoker · Oct 31, 2015

It is unlikely this kind of corrosion could be galvanic, more likely stray current. Get your electrical system checked by an ABYC Certified Corrosion Analyst.

CORROSION PHOTO ALBUM - Take a look at the photo in the far right column, 9th row. It is an x-ray of a 1mm pit on the surface of a prop shaft ,inside the shaft was a 1.5cm cavity. Sorry, IMHO your shafts are done.

PS. I am an ABYC Certified Corrosion Analyst.

psneeld · Oct 31, 2015

boatpoker said:
It is unlikely this kind of corrosion could be galvanic, more likely stray current. Get your electrical system checked by an ABYC Certified Corrosion Analyst.

CORROSION PHOTO ALBUM - Take a look at the photo in the far right column, 9th row. It is an x-ray of a 1mm pit on the surface of a prop shaft ,inside the shaft was a 1.5cm cavity. Sorry, IMHO your shafts are done.

PS. I am an ABYC Certified Corrosion Analyst.

Sure it's not just crevice corrosion from stagnant water under the packing?

pic courtesy of Cox Engineering.

It does look pretty bad either way, Rudder shafts? If the shop could either x-ray or turn to good metal...but then the cost of new may not be much further. Prop shafts...probably new is the deal unless those could definitely be x-rayed and certified. Unless the shop has different techniques I'm not familiar with.

Capt.Bill11 · Oct 31, 2015

psneeld said:
Sure it's not just crevice corrosion from stagnant water under the packing?

+1

And I bet they are repairable.

http://highseasyachtservice.com/wp-content/uploads/2011/10/Marine-Shaft-Crevice-Corrosion1.pdf

Of course since they're rudder shafts they would probably go another 10-20 years as is.

angus99 · Oct 31, 2015

Thanks, again, guys. I'll get a proper hands-on evaluation, x-Ray or whatever it takes before deciding to repair or replace.

Gurryman, I appreciate the lead. Will probably give Turnwright a call Monday. The shaft is 2.75" in diameter.

Wallace, in rereading my survey, the stbd rudder assembly had no attachment to the bonding system and the port assembly had excessive resistance. I haven't verified it with the yard yet, but I'm betting the stbd post is the one with the worst corrosion. Most of the damage is confined to the area that would have been in the packing gland--in constant contact with salt water and, I assume, no oxygen. On the other hand, the zincs on both rudders are eroding at about the same rate. The galvanic isolator was checked during the survey and reportedly OK.

boatpoker · Oct 31, 2015

psneeld said:
Sure it's not just crevice corrosion from stagnant water under the packing?

I agree that is possible but only if the boat sat for years without the shaft moving thereby allowing stagnant water to be held against the shaft.
Either way it's not repairable in my opinion.

If you look at the photo immediately to the left of the x-ray photo you'll see that it is of a broken shaft. The shaft broke from crevice corrosion when the boat was moved for the first time on over 10years. Take a look at the pitting on the unbroken part, it is less severe than the OP's

cappy208 · Oct 31, 2015

Reading your posts it appears you have twin screw. If so then you have another rudder to get home on. So do the flash, replate and machine. But remember that this issue is cumulative and will require full repair soon.

Capt.Bill11 · Nov 1, 2015

cappy208 said:
Reading your posts it appears you have twin screw. If so then you have another rudder to get home on. So do the flash, replate and machine. But remember that this issue is cumulative and will require full repair soon.

Heck, on a twin screw boat they could both fall off and you could get to a dock just fine.

Northern Spy · Nov 1, 2015

Looks like regular old pitting corrosion (as much as one can tell from a photo). Here is what would generally be required to repair each shaft.

Remove shaft from rudder. Chuck shaft up in lathe. Skim cut material away from corroded area, until defect is visually gone. (More you remove, the more weld you have to deposit). 0.125-0.200" will probably clean it up. If machinist goes more than SAY 0.250-0.300" consider machining new shafts. Be sure to chamfer or radius transition. Conduct Liquid Penetrant Inspection (LPI) of affected area to check for cracks or pits. Skim cut again if required. Weld metal build up with GTAW (tig), distributing heat evenly. Ensure weld cap is adequately proud to nominal diameter. Machine back to a few thou above nominal. Buff with emory and crocus cloth to nominal, achieving a finish of around 4 micro" Ra. LPI final repair to check for indications.

The tough part is picking the filler material for the weld. It is probably an austenitic stainless steel (300 grade). 316 on 316 is appropriate, 304 on 304, etc. Many welders will choose 309 for an unknown SS. The problem with that is that it has no molybdenum, which arguably makes it more susceptible to crevice corrosion and pitting later on.

You could see if any fab shops have the ability for Positive Material Identification with an XRF gun. It's possible, as the price on these guns have gone down a lot recently.

This is a very common repair methodology. Consider seeking out a pump repair shop or other industrial fab shop. Easy peasy.

psneeld · Nov 1, 2015

Northern Spy said:
Looks like regular old pitting corrosion (as much as one can tell from a photo). Here is what would generally be required to repair each shaft.

Remove shaft from rudder. Chuck shaft up in lathe. Skim cut material away from corroded area, until defect is visually gone. (More you remove, the more weld you have to deposit). 0.125-0.200" will probably clean it up. If machinist goes more than SAY 0.250-0.300" consider machining new shafts. Be sure to chamfer or radius transition. Conduct Liquid Penetrant Inspection (LPI) of affected area to check for cracks or pits. Skim cut again if required. Weld metal build up with GTAW (tig), distributing heat evenly. Ensure weld cap is adequately proud to nominal diameter. Machine back to a few thou above nominal. Buff with emory and crocus cloth to nominal, achieving a finish of around 4 micro" Ra. LPI final repair to check for indications.

The tough part is picking the filler material for the weld. It is probably an austenitic stainless steel (300 grade). 316 on 316 is appropriate, 304 on 304, etc. Many welders will choose 309 for an unknown SS. The problem with that is that it has no molybdenum, which arguably makes it more susceptible to crevice corrosion and pitting later on.

You could see if any fab shops have the ability for Positive Material Identification with an XRF gun. It's possible, as the price on these guns have gone down a lot recently.

This is a very common repair methodology. Consider seeking out a pump repair shop or other industrial fab shop. Easy peasy.

Thanks for the expertise.

Nice to know exactly what goes into the time between dropping off the shaft and breaking out the credit card...and why it cost more than a Big Mac.

Art · Nov 1, 2015

Northern Spy said:
Looks like regular old pitting corrosion (as much as one can tell from a photo). Here is what would generally be required to repair each shaft.

Remove shaft from rudder. Chuck shaft up in lathe. Skim cut material away from corroded area, until defect is visually gone. (More you remove, the more weld you have to deposit). 0.125-0.200" will probably clean it up. If machinist goes more than SAY 0.250-0.300" consider machining new shafts. Be sure to chamfer or radius transition. Conduct Liquid Penetrant Inspection (LPI) of affected area to check for cracks or pits. Skim cut again if required. Weld metal build up with GTAW (tig), distributing heat evenly. Ensure weld cap is adequately proud to nominal diameter. Machine back to a few thou above nominal. Buff with emory and crocus cloth to nominal, achieving a finish of around 4 micro" Ra. LPI final repair to check for indications.

The tough part is picking the filler material for the weld. It is probably an austenitic stainless steel (300 grade). 316 on 316 is appropriate, 304 on 304, etc. Many welders will choose 309 for an unknown SS. The problem with that is that it has no molybdenum, which arguably makes it more susceptible to crevice corrosion and pitting later on.

You could see if any fab shops have the ability for Positive Material Identification with an XRF gun. It's possible, as the price on these guns have gone down a lot recently.

This is a very common repair methodology. Consider seeking out a pump repair shop or other industrial fab shop. Easy peasy.

Why Gilligan... Had you performed that process to the SS Minnow's UW shafts maybe Thurston Howell could have gotten back to land, become even richer and bought you and The Skipper a brand new tour boat. I had no Idea you knew sooo much about metallurgy.

FF · Nov 1, 2015

Rudder shafts are usually specked with a huge safety margin.

Turning 1/8 or 1/16 off them will not change their service life.

angus99 · Nov 1, 2015

Northern Spy said:
Looks like regular old pitting corrosion (as much as one can tell from a photo). Here is what would generally be required to repair each shaft.

Remove shaft from rudder. Chuck shaft up in lathe. Skim cut material away from corroded area, until defect is visually gone. (More you remove, the more weld you have to deposit). 0.125-0.200" will probably clean it up. If machinist goes more than SAY 0.250-0.300" consider machining new shafts. Be sure to chamfer or radius transition. Conduct Liquid Penetrant Inspection (LPI) of affected area to check for cracks or pits. Skim cut again if required. Weld metal build up with GTAW (tig), distributing heat evenly. Ensure weld cap is adequately proud to nominal diameter. Machine back to a few thou above nominal. Buff with emory and crocus cloth to nominal, achieving a finish of around 4 micro" Ra. LPI final repair to check for indications.

The tough part is picking the filler material for the weld. It is probably an austenitic stainless steel (300 grade). 316 on 316 is appropriate, 304 on 304, etc. Many welders will choose 309 for an unknown SS. The problem with that is that it has no molybdenum, which arguably makes it more susceptible to crevice corrosion and pitting later on.

You could see if any fab shops have the ability for Positive Material Identification with an XRF gun. It's possible, as the price on these guns have gone down a lot recently.

This is a very common repair methodology. Consider seeking out a pump repair shop or other industrial fab shop. Easy peasy.

Brilliant!!! Thanks a ton, Spy. Pump repair specialists (minus the "marine" inflator) will be the first place I look. It will be immensely helpful to walk into a shop and have some idea of what to expect. I will post the outcome of this little drama when I have it fixed.

Northern Spy · Nov 1, 2015

FF said:
Rudder shafts are usually specked with a huge safety margin.

Turning 1/8 or 1/16 off them will not change their service life.

I kind of thought about that too. I agree there may be a margin. But rudder stock loads are dependent upon the type, size, and arrangement of the rudder and (number of) bearing. It will have inherently different mechanical loads than a prop or pump shaft.

Depending on the age and hereditary of the boat, calculations may not even been involved in its fabrication or sizing.

Other options to consider.

If there is adequate strength with the remaining diameter, one could consider skim cutting and using a Belzona (1111 super metal is common) build up instead of weld filler.

A good machine shop may also be able to machine off and shrink a sleeve on as well.

Thermal metal spray (HVOF, HVLF) build up is another option.

All of these have the advantage of replacing the corroded area with a non or less corrosion susceptible material.

I thought I downloaded some rudder stock sizing calculations at one time. I'll see if I can dig them up.

Keep in mind, the stuff I am responsible for fixing is industrial, runs 24/7, and is expected to last. There's 8760 hours in a year. I'm trying to get 50,000 hrs out of my repairs. But I also figure, if one is going to all of the work to take it apart and suffer the downtime, it is only incremental cost and time to do it right.

I think that doing a skim cut to a smaller diameter without build up may just lead to leaks or problems later on.

Northern Spy · Nov 1, 2015

I forgot to mention in my previous post to check radial runout before and after the repair. Anyone actually doing this type of work would do this automatically.

And you can also use SAW welding. A pump shop might be set up for that.

I wouldn't use MIG welding as it is pretty low amperage and more susceptible to incomplete penetration and porosity. Just saying that in case a buddy had a lathe and MIG welder at home.

angus99 · Nov 1, 2015

Northern Spy said:
I forgot to mention in my previous post to check radial runout before and after the repair. Anyone actually doing this type of work would do this automatically.

And you can also use SAW welding. A pump shop might be set up for that.

I wouldn't use MIG welding as it is pretty low amperage and more susceptible to incomplete penetration and porosity. Just saying that in case a buddy had a lathe and MIG welder at home.

What are you doing next week? I've got some frequent flier miles I can send your way . . .

angus99 · Feb 9, 2016

Update

I got the rudder shafts back from the specialty shop yesterday and the work looks to be excellent. They ground away the pitted surface to solid metal and built it back up with Inconel 625. They like this alloy with marine applications, including with graphite packing. Measuring equipment might be able to distinguish a difference in diameters, but the transitions from old to new material feel perfect. Not cheap but not as hard on the wallet as I was expecting. Here are some before and after shots.

Northern Spy · Feb 9, 2016

Inconel 625 is an excellent choice. Sounds like you found the right shop!

angus99 · Feb 9, 2016

Northern Spy said:
Inconel 625 is an excellent choice. Sounds like you found the right shop!

I was REALLY hoping you were going to say that. Thanks!

sunchaser · Feb 9, 2016

angus99 said:
I was REALLY hoping you were going to say that. Thanks!

Spy has given you the correct advice for the past few months. Inconel products have been used for this application for close to a century with great success. BTW, Inconel is an acronym for the long lived Inco mining and metals company that became famous for their variety of nickel products including Monel, named after the President of Inco - Monell - in 1906.

I am unfortunately saddled with a degree in Metallurgical Engineering and slobber all over this stuff and the guys like Spy who really make it work. Smart of you to listen to him Angus.

bayview · Feb 9, 2016

looks like beautiful work. Amazing what skilled craftsmen can accomplish

angus99 · Feb 9, 2016

Thanks, SC. When Spy talks, I listen. Simply finding a business that catered to heavy industry, vs marine, saved me money.

I have actually been to Sudbury and seen the giant nickel!

ImageUploadedByTrawler Forum1455034436.322950.jpg

Art · Feb 9, 2016

Damn great to have such a diverse, knowledgeable group of contributors on TF. I'm looking to utilize Ian's truly top tier workmanship company for similar shaft restoration needs as they may arise.

My hat's off to you all!

Happy Smart-Accomplishment ~~Daze! - Art~~

Pitted Rudder Shafts

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