150 ft yacht with 130mm shafts. Problems with shafts. 2

[captstaats]

Hello Everyone,

I am new to this site and could really use some information. I have two shafts 130mm with heavy pitting that I need to have resurfaced and machined. I am probably not using the correct terminology please bear with me. Some of the pitting is 1/2" deep but I have heard that the shafts can have a new surface applied through a welding process and machining. Is there a depth of corrosion that decides when it is time to scrap the shafts? The yacht is in Miami,FL, if someone knows of a reputable machine shop that can handle this type of job please let me know. Or if I am missing important information about the process I am all ears. The spots in question are between two bearings. Please see the attachment for a picture of the corrosion.

 

[MikeHalloran]

Florida has a lot of coastline, and a lot of marine service centers. If you want local info, you need to define your locale a little more specifically.

Or, you could just ask the nearest yacht yard, or the one you're in; they all have trusted suppliers for most everything, including weld repair of shafts.



Mike Halloran
Pembroke Pines, FL, USA

 

[EdStainless]

I would think twice, 1/2" into a shaft is deep, and you will not have as good of strength or corrosion resistance as you started with.
What material are they?
It sounds like you really need to consider an upgrade in the alloy.

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P.E. Metallurgy, Plymouth Tube

 

[captstaats]

Thanks guys for the response. The shafts were replaced in Italy July 2012, I had to use google translator to get the basic information of replacing shafts and bearings. No other info was given on the invoice. If you look at the picture it doesn't even look like SS. I am in Miami would prefer to hear someone say they know a shop that is reputable. What would they have to do to test the metal for type of SS?

 

[MikeHalloran]

We can't look at the picture, because there's no attachment.


Mike Halloran
Pembroke Pines, FL, USA

 

[captstaats]

Not sure why the pics didn't upload. Will try again. Behind the packing gland is the first bearing then 4 ft further is the stern tube bearing. It seems as though the bearings are trapping water. Research indicates in time the salinity increases as well as oxidation lowering the O2 content accelerating the corrosion process. Is that correct? Is there a formula for distance between bearings for a 130mm shaft? I have never seen bearings so close together and that is where the heavy pitting has taken place. I also noticed the first bearing is worn substantially more than the other 3. I see your location is Pembroke pines do you do SS shaft work there?
Thanks again for sharing your professional experience and advice.

 

[EdStainless]

Often for seawater service yachts are equipped to pump a small amount of fresh water into the bearings, to help keep salinity down.
I don't know any boat people down there, but there are a lot.
I'll ask a friend in Palm Beach who he uses.

There are special alloys used for seawater service. A low alloy stainless grade would last forever in fresh water and even handle occasional runs in seawater. But sitting in seawater take a different class of material.

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P.E. Metallurgy, Plymouth Tube

 

[MikeHalloran]

Wow, that is nasty. I can't say I've ever seen corrosion that highly localized and deep. Given that, I wouldn't trust the remainder of the shafts.

No, I don't do shafts. I worked on yacht exhausts all over SoFla for a few years, so I got to see a bunch of them spinning, none like yours.

You might consider mechanical seals to replace the packing glands.


Mike Halloran
Pembroke Pines, FL, USA

 

[captstaats]

Thanks for responding guys, I like the idea of pumping fresh water through the gland while we are just sitting alongside. There is a fitting from the engine raw water cooling side that goes to the backing of the packing which could be tied into. This would push the salt water out and keep the shafts in good shape. Thanks for a simple remedy. I have never see SS shafts do that type of deterioration I wonder if the Italians got their steel from the Chinese??? I will approach a few shops in the am to see if they can do anything with them. Will update as things move along.

 

[tbuelna]

The shaft shown in the photos looks like it already had some weld repairs performed on it. And given the current state of the shaft I can't imagine it would be cost effective to try to salvage it versus machining a new one.

 

[captstaats]

In Italy they supposedly replaced the shafts July 2012 for the same issue. Unless they told the owner they were new shafts and machined the old ones? What do you see that makes you think they have been machined before?

 

[weldstan]

First determine the alloy. There are NDE Labs in the area that can perform XRF PMI (Positive Material Identification. I also believe that at least one lab in S. Florida can perform PMI with optical emission spectroscopy. Then a more corrosion resistant material can be selected or additional operating parameters (fresh water injection proposal) can be installed. From its past history, localized welding repair with matching weld filler metals or more corrosion resistant weld filler metals will not provide increased service life.

Is this yacht operated frequently or does it sit at dock for long periods?

 

[captstaats]

The yacht traveled the world but now sits and waits for a new owner. I have talked with F&J propeller in Miami who will look at making new shafts with better material. Talking about turning 5.5" shafts to 130MM. How does that effect the SS once it has been turned down to size. Thanks for all of the great info this is what the web was meant for!

 

[EdStainless]

Unless the shafts are heavily cold worked to make them stronger turning them down will have no impact.
You should be looking at alloys with high Cr and Mo.
Such as Aquamet 22, here:

http://www.aquamet.com/home.nxg

This isn't a commercial plug, but I have seen their stuff used successfully in many applications.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

thread330-158713

 

[metengr]

Save yourself some time and utilize the search feature above.

Another example

thread330-179251

 

[stevenal]

Do you have cathodic protection on the shaft?

 

[captstaats]

Guys thanks for leading me to Brian at Aquamet, it appears the Italians put in the 17 instead of the 22HD or 25. This is why the magnet sticks to it like it does the hull plating. There is Cathodic protection and monitoring which is within the normal range. I will be adding a potable water flush to keep the salinity down in the space and replace the shafts with a higher quality. Thanks for all of the great advice and input greatly appreciated.

 

[EdStainless]

But the way, I have been wanting to ask, what is the boat?
A pair of 1,500 hp engines in a 150' boat is quite a package.

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P.E. Metallurgy, Plymouth Tube

 

[captstaats]

She is an Italian built full displacement hull and can be seen at

http://www.goldencompass.biz